Selina ICSE Solutions

Selina Concise Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

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Selina Concise Chemistry Class 7 ICSE Solutions – Elements, Compounds and Mixtures

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Chemistry Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 7 Chemistry Chapter 3 Elements, Compounds and Mixtures

Points to Remember :

  1. Every substance is made up of very tiny particles, called molecules. Molecules are formed from even smaller particles called atoms.
  2. Element— (a) Element is the simplest pure substance. It cannot be divided further into simpler substances by any chemical method, e.g. oxygen, hydrogen, sulphur, etc.
    (b) At present 116 elements are known, of which 92 are natural elements.
  3. Based on their properties, elements are classified into : metals, non-metals, metalloids, noble gases.
  4. Metals are ductile, malleable, good conductors of heat and electricity, high melting and boiling points. Metals are sonorous, e.g., Iron, Gold, Silver, etc.
  5. Non-metals are solids and brittle in nature, bad conductor of heat and electricity (exception Graphite) low melting and boiling points, e.g. sulphur, carbon, hydrogen, etc.
  6. Metalloids— These elements show properties of both metals and non-metals. They are hard solids, e.g. Boron, Silicon, Arsenic.
  7. Inert or noble gases— These elements do not react chemically with other elements or compounds are called noble (Inert) gases, e.g., helium, neon, argon, etc.
  8. Symbols of Elements— Each element is denoted by a symbol usually to first letter.
    Examples : Oxygen by O Hydrogen by H.
  9. Atom— “An Atom is the smallest particle of an element that can take part in a chemical reaction but may or may not have independent existence.”
    The atom of an element exhibits all the properties of that element.
  10. Molecule— A molecule is the smallest particle of a pure substance of element or compound which has independent existence. It exhibits all the properties of pure substance.
  11. Atomicity— The number of atoms of an element that join together to form a molecule of that element is known as the atomicity.
  12. Molecular Formula— of an element is the symbolic representation of its molecule. It indicates the number of atoms present in it. e.g. Magnesium oxide – MgO.

EXERCISE – I

Question 1.
Write the symbols of helium, silver, krypton, antimony, barium.
Answer:

Element                   Symbol
Helium                         He
Silver                            Ag
Krypton                       Kr
Antimony                    Sb
Barium                        Ba

Question 2.
Write the names of following elements Na, C, Kr, U, Ra, Fe, Co.
Answer:

Symbol           Element
Na                        Sodium
C                          Carbon
Kr                        Krypton
U                         Uranium
Ra                        Radium
Fe                           Iron
Co                        Cobalt

Question 3.
Define :

  1. Elements : An element is the basic form of matter that cannot be broken down into simpler substances by chemical reactions.
  2. Compounds : A compound is a pure substance formed by the chemical combination of two or more elements in a fixed ratio by mass.

Question 4.
Name the main metal present in the following :
Answer:

(a) Haemoglobin                                    Iron
(b) Chalk                                               Calcium
(c) Chlorophyll                                   Magnesium
(d) Chocolate wrappers                    Aluminium

Question 5.
Give four examples of non-metallic elements.
Answer:
Examples : Hydrogen, oxygen, nitrogen, carbon, chlorine, sulphur, phosphorus, etc.

Question 6.
What do you understand by :
Answer:

  1. Metalloids : Metalloids are those substances which have some properties of metals and some of non-metals e.g. boron, silicon.
  2. Noble gases : Noble gases are those which do not react chemically with other elements or compounds e.g. helium, neon, etc.

Question 7.
Select elements and compounds from the following list: Iron, plaster of paris, chalk, common salt, copper, aluminium, calcium oxide, cane sugar, carbon, silica, sodium sulphate, uranium, potassium carbonate, silver, carbon dioxide.
Answer:
Selina Concise ICSE Solutions for Class 7 Chemistry Chapter 3 Elements, Compounds and Mixtures-7

EXERCISE – II

Question 1.
State four difference between compounds and mixtures.
Answer:

Compound Mixture
1. A compound is a pure substance. 1. A mixture is an impure substance.
2. Compounds are always homogeneous. 2. Mixtures may be homogeneous or heterogeneous.
3. A compound has a fixed composition, i.e., it is formed when two or more pure substances chemically combine in a definite ratio by mass. 3. A mixture has no fixed composition, i.e., it is formed by mixing two or more substances in any ratio without any chemical reaction.
4. Formation of a compound involves change in energy. 4. Formation of a mixture does not involve any change in energy.
5. Compounds have specific set of properties. 5. Mixtures do not have any specific set of properties.
6. Components of compounds can be separated only by complex chemical processes. 6. Components of mixtures can be separated by simple physical methods.

 Question 2.
What are the characteristic properties of a pure substance? Why do we need them?
Answer:
Pure substance : Pure substances have a definite set of properties such as boiling point, melting point, density, etc. They are all homogeneous i.e., their composition is uniform throughout the bulk. Both elements and compounds are pure substances.
Pure substances are needed to :

  1. Manufacture medicines.
  2. To prepare chemicals in industry.
  3. For scientific purposes.
  4. To maintain the good health of human beings.

Question 3.
Give two examples for each of the following :
(a) Solid + Solid mixture
(b) Solid + Liquid mixture
(c) Liquid + Liquid mixture
Answer:
(a) Solid + Solid mixture :Sand and sugar,

  • Sand and stone,
  • sand and sugar.

(b) Solid + Liquid mixture :

  • Sand and water,
  • Charcoal and water.

(c) Liquid + Liquid mixture :

  • Oil in water,
  • Alcohol and water.

Question 4.
Define :

  1. Evaporation : Is the process ~of converting a liquid into its vapours state either by exposing it to air or by heating.
  2. Filtration : The process of separating solid particles from liquid by allowing it to pass through a filter paper is called filtration.
  3. Sublimation : The process in which a solid changes directly into its vapours on heating is called sublimation.
  4. Distillation : Distillation is the method of getting a pure liquid from a solution by evaporating and then condensing the vapours.
  5. Miscible liquids : Homogeneous liquid-liquid mixtures are called miscible liquids.
  6. Immiscible liquids : Heterogeneous liquid-liquid mixtures are called immiscible liquids.

Question 5.
Name the process by which the components of following mixtures can be separated.

  1. Iron and sulphur
  2. Ammonium chloride and sand
  3. Common salt from sea water
  4. Chaff and grain
  5. Water and mustard oil
  6. Sugar and water
  7. Cream from milk

Answer:

  1. Magnetic separation.
  2. Sublimation.
  3. Evaporation.
  4. Winnowing separates chaff (lighter) from heavier grains in two different heaps.
  5. Mustard oil and water is liquid-liquid immiscible mixture and is separated by separating funnel. Water being the heavier forms the lower layer.
  6. By evaporation in this process of converting a liquid into its vapour state by heating. Liquid is heated and water evaporate and sugar is obtained.
  7. Centrifugation.

Question 6.
How will you separate a mixture of common salt, chalk powder and powdered camphor? Explain.
Answer:
Comphor with sublimation. Chalk powder by Alteration then the residual left is common salt.

Question 7.
How is distillation more advantageous than evaporation?
Answer:
The advantage of distillation is that both components of the
solid and liquid mixture are obtained. Whereas in evaporation only solid is obtained.

Question 8.

  1. What is chromatography?
  2. Why is it named so?
  3. What are the advantages of chromatography?
  4. Name the simplest type of chromatography?
  5. On what principle is this method based?
  6. What is meant by stationary phase and mobile phase in chromatography?

Answer:

  1. The process of separating different dissolved constituents of a mixture by their absorption on an appropriate material is called chromatography.
  2. It is named so, because earlier it was used to separate mixtures containing coloured components only but these days this technique is applied to colourless substances too.
  3. Advantages of chromatography :
    (i) A very small quantity of the substance can be separated.
    (ii) Components with very similar physical and chemical properties can be separated.
    (iii) It identifies the different constituents of a mixture.
    (iv) lt also helps in quantitative estimation of components of a mixture.
  4. The simplest type of chromatography is “Paper chromatography”.
  5. Chromotography is based on differential affinities of compounds towards two phases i.e. stationary and mobile phase.
  6. The filter paper acts as “stationary phase” while the solvent act as “mobile phase”.

Question 9.
On what principle are the following methods of separation based? Give one example of a mixture for each of the methods mentioned in which they are used
Answer:

  1. Sublimation : Change of solid into vapours directly on heating and change of vapours into solid again on
    Example : Salt from ammonium chloride.
  2. Filtration : The process of separating insoluble solid particles from a liquid by allowing it to pass through a filter is called Alteration. These filters allow liquids to pass through them but not solids. The insoluble solid left on the filter is called the residue, while the liquid which passes through the filter is called the filtrate. Mixtures like chalk and water, clay and water, tea and tea leaves, sawdust and water, etc., are separated by this method.
  3. Sedimentation and decantation : The settling down of suspended, insoluble, heavy, solid particles in a solid- liquid mixture when left undistrubed is called sedimentation.
    The solid which settles at the bottom is called sediment while the clear liquid above it is called supernatant liquid.
    The process of pouring out the clear liquid, without disturbing the sediment, is called decantation.
    Example : A mixture of sand and water.
  4. Solvent extraction method : This method is used when one of the solid components is soluble in a liquid.
    Example : A mixture of sand and salt can be separated by this method. Salt gets dissolved in water while sand settles down in the container. The salt solution is then decanted. Salt is separated from the solution by evaporation. In this way, they can be separated.
  5. Magnetic separation : This method is used when one of the components of the mixture is iron. Iron gets attracted towards a magnet and hence can be separated. Mixtures of iron and sulphur, iron and sand, etc., can be separated by moving a magnet over them. Iron gets attached to the magnet and is separated.
  6. By using a separating funnel : It is a simple device used to separate the components of a liquid-liquid heterogeneous mixture.
    Example : Kerosene oil and water. The mixture is placed in a separating funnel and allowed to stand for sometime. The components form two clear layers. Water being heavier forms the lower layer and oil being lighter forms the upper layer. When the stopper of the funnel is opened, the heavier liquid trickles out slowly and is collected in a vessel. The stopper is closed when the bottom layer is entirely removed the funnel. In this way, the two liquids are separated.
  7. Fractional distillation : The process of distillation is used for separating the components of a homogeneous liquid-liquid mixture, like water and alcohol. This is based on the fact that alcohol boils at a lower temperature than water. The vapour of alcohol are collected and cooled while water is left behind in the original vessel. Thus, two liquids having different boiling points can be separated by distillation provided that difference in their boiling points must be 25 °C or more.

OBJECTIVE TYPE QUESTIONS

Question 1.
Fill in the blanks:
Answer:

  1. Elements are made up of same kind of atoms.
  2. Elements and compounds are pure substances.
  3. In a mixture the substances are not combined chemically.
  4. Clay is separated from water by the method called loading and decantation.
  5. Crystallisation is a process to obtain a very pure form of a solid dissolved in a liquid.
  6. Camphor and ammonium chloride can sublimate.

Question 2.
Give one word answers for the following :
Answer:

  1. The solid particles which remain on the filter paper after the filtration residue.
  2. The liquid which evaporates and then condenses during the process of distillation distillate.
  3. The process of transferring the clean liquid after the solid settles at the bottom of the container decantation.
  4. The process by which two miscible liquids are separated fractional distillation.

MULTIPLE CHOICE QUESTIONS

Select the correct alterative from the choices given for the following statements:
Question 1.
A pure liquid is obtained from a solution by :
Answer:

  1. evaporation
  2. distillation
  3. Alteration
  4.  crystallisation

Question 2.
Components of crude petroleum can be separated by :
Answer:

  1. distillation
  2. evaporation
  3. filtration
  4. fractional distillation

Question 3.
Example of a homogeneous mixture is :
Answer:

  1. tap water 
  2. distilled water
  3.  sand and water
  4. water and oil

Question 4.
In chromatography the filter paper is :
Answer:

  1.  stationary phase 
  2. mobile phase
  3. mixture
  4. none of the above

Question 5.
A set of mixture is :
Answer:

  1.  ink, honey, icecream, milk
  2. tapwater, gold, common salt, alloy
  3.  milk, brass, silver, honey
  4. butter, petroleum, tapwater, iron

 

Selina Concise Biology Class 7 ICSE Solutions – Allergy

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Selina Concise Biology Class 7 ICSE Solutions – Allergy

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Biology for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 7 Biology Chapter 7 Allergy

Review Questions

Question 1.
Define the term “allergy”.
Answer:
Allergies, also known as allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes no adverse effects to most people. These diseases include hay fever, dermatities, asthma, food allergies, etc.

Question 2.
Name the inflammatory chemical released by the basophils causing skin reaction and construction of the bronchioles.
Answer:
The histamine causes inflammation, skin rash and constriction of the bronchioles (as in asthma).

Question 3.
How the allergy causing chemical is naturally removed from the body ?
Answer:
There are no permanent cure for an allergy. Medication for allergies do give relief. Those people prone to allergic reactions should be aware of the allergens that trigger these responses in their bodies and avoid them completely, especially food and medicines. Allergy shots are helpful to those with seasonal allergies like those caused by pollen.

4. Match the items given under column I with those given under column II.
column I                                         column II
Selina Concise Biology Class 7 ICSE Solutions - Allergy 1
Answer:
              column I                                         column II
Selina Concise Biology Class 7 ICSE Solutions - Allergy 2
Question 5.
Name any three routes of which allergens normally enter in our body.
Answer:

  1. Skin — Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema.
  2. Mouth — A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods’are caused by cow’s milk, soy, eggs, wheat, peanuts, tree nuts, fish and shellfish.
  3. Nose — Pollen, spores, dust particles and certain chemicals find entry through the nose.

Question 6.
What are allergens ? Name any three allergens.
Answer:
The substances that cause allergies are called allergens.

  1. Dust particles
  2. Nuts
  3. Pollen

Question 7.
Name the two tests generally used to diagnose allergy and describe any one of them.
Answer:

  1. Prick Test—Skin prick test is also known as “puncture testing” or “prick testing” due to the series of tiny punctures or pricks made into the patients skin. A small plastic or metal device is used to puncture or prick the skin. Sometimes, the allergens are injected intradermally into the patients skin, with a needle and syringe. Small amounts of suspended allergens or their extracts (e.g., pollen grain, insect sting proteins, peanut extracts) are introduced to sites on the skin marked with pen or dye. Common areas for testing include the inside of forearm and the back.
  2. Blood Testing — A sample of the patient’s blood is sent to a laboratory for analysis. Multiple allergence can be detected with a single blood sample.
    The test measures the concentration of specific antibodies in the blood. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity.

Question 8.
Which test is mostly favoured for testing allergy, prick test or blood test ? Why ?
Answer:
Blood test is mostly favoured for testing allergy.

Blood Testing — A sample of the patient’s blood is sent to a laboratory for analysis. Multiple allergence can be detected with a single blood sample.
The test measures the concentration of specific antibodies in the blood. The quantitative allergy blood result can help determine what a patient is allergic to, help predict and follow the disease development, estimate the risk of a severe reaction, and explain cross-reactivity.

Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System

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Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 6 The Circulatory System. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 8 Biology Chapter 6 The Circulatory System

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) The only artery which carries deoxygenated blood is called,

  1. Hepatic artery
  2. Pulmonary artery
  3. Aorta
  4. Renal artery

(b) Pulmonary vein carries

  1. Oxygenated blood
  2. Deoxygenated blood
  3. Glucose-deficient blood
  4. CO2 laden blood

(c) Function of WBCs is to

  1. Transport oxygen
  2. Help in clotting of blood
  3. Provide immunity
  4. Provide storage of food.

(d) Blood Capillary is a

  1. Broad tube
  2. Artery with thick wall
  3. Vein with large lumen
  4. Narrow tube made up of endothelium only.

(e) Nucleus is absent in 

  1. RBCs
  2. WBCs
  3. All blood cells
  4. Liver cells.

(f) Sphygmomanometer measures

  1. Pulse rate
  2. Heart beat
  3. Blood pressure
  4. Brain activity

(g) The blood tastes saltish due to the presence of dissolved:

  1. Sodium chloride
  2. Potassium chloride
  3. Ammonium nitrate
  4. Sodium nitrate

Short Answer Questions:

Question 1.
1. Differentiate between the following pair of terms:
(a) Pulmonary artery and pulmonary vein.
(b) Vena cava and aorta.
(c) Platelets and WBC.
(d) RBC and WBC Ans.
Answer:
(a) Pulmonary artery and pulmonary vein.

Pulmonary artery Pulmonary vein
1. This involves circulation of blood from the heart to the lungs. 1. This involves circulation of blood to the heart from the lungs.
2. It carries deoxygenated blood. 2. It carries oxygenated blood.

(b) Vena cava and Aorta

Vena Cava Aorta
1. Vena Cava is a large vein. 1. Aorta is the large artery.
2. It carries deoxygenated blood from the upper and lower parts of the body i.e. head and shoulders. 2. It carries oxygenated blood to all parts of the body through its branches.

(c) Blood platelets and blood group.

Platelets WBC
1. These are colourless, oval or round, cytoplasmic fragments 1. WBC are colourless and lack haemoglobin, larger in quantity, and have distinct oval and lobed nucleus.
2. These play a major role in blood clotting. 2. They prevent body from disease causing germs by providing immunity
3. Their life span is 3-5 days and it is called thrombocytes. 3. Their life span is short i.e. 5 to 20 days.

(d) RBC and WBC

RBC WBC
1. They do not have nucleus at maturity. 1. They have a large characteristic nucleus.
2. They possess haemoglobin and are red. 2. They are colourless as they have no pigment.
3. They help in transport of respiratory gases. 3. They help in defence mechanism.

Question 2.
Give any three differences between an artery and a vein:
Answer:
Following are the differences between the artery and a vein:

Artery Vein
1. Arteries carry blood from the heart to various body parts. 1. Veins carry blood from different body parts to the heart.
2. These carry oxygenated blood (except the pulmonary artery). 2. These carry deoxygenated blood (except the pulmonary vein).
3. B lood flows with h igh speed and under high pressure. 3. Blood flows with low speed and under low pressure.

Question 3.
Fill in the blanks with suitable words given below:
Answer:
a. The two lower chambers of the heart are called ventricles.
b. The pulmonary artery takes the blood from the ventricles to the lungs.
c. The blood loaded with carbon dioxide from the body comes into the right auricle of the heart.
d. The oxygen-rich blood from the lungs comes into the left ventricle of the heart.
e. The oxygen-rich blood is pumped into different parts of the body through aorta.
f. The carbon dioxide loaded blood from right ventricle is pumped into the lungs through pulmonary artery.
g. The instrument used to find out the blood pressure is known as sphygmomanometer.
h. The colour of a red blood cell is due to haemoglobin.
i. The blood plasma contains a dissolved substance called fibrinogen.
j. The liquid part of coagulated blood is known as serum.

Question 4.
In which organ of our body does blood get oxygenated?
Answer:
Blood becomes oxygenated in the lungs. The oxygenated blood is returned to left verticles by the pulmonary vein.

Question 5.
Which side of the heart (left or right) contains oxygenated blood?
Answer:
The left side of the heart contains oxygenated blood.

Question 6.
What is the role of haemoglobin in the blood ?
Answer:
The haemoglobin is the respiratory pigment which is formed of the iron containing part known as haemin and protein part known as globin. It helps to transport respiratory gases (oxygen).

Question 7.
Name the disease in which the number of platelets reduces to 25,000 – 30,000 per cubic mm of blood. State its major symptoms.
Answer:
Dengue fever is one such disease in which the number of platelets get reduced to as low as 25-30 thousands per cubic mm of blood. The major symptoms of dengue are high fever, rashes or red spots on body, nausea or vomiting, pain in abdomen, back, or back of the eyes and muscles.

Long Answer Questions:

Question 1.
 Given alongside is a diagram of human heart showing its internal structures. Label the parts marked 1 to 6, and answer the following questions.
Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System 1
(a) Which type of blood is carried by the blood vessel marked 2?
(b) Name the main artery which takes the blood from heart to different parts of the body?
(c) Which chamber of the heart receives deoxygenated blood from the body?
Answer:

  1. Left pulmonary artery
  2. Superior vena cava
  3. Left pulmonary vein
  4. Right auricle
  5. Left auricle
  6. Left ventricle

(a) Deoxygentated blood.
(b) Aortic arch (Aorta).
(c) Right Atrium

Question 2.
You can see some blood vessels on the outside of the hands specially in older people. Are those veins or arteries ? How can you confirm your answer ?
Answer:
In older persons the skin becomes loose as the fat below becomes less with age and the vessels passing through these areas especially on the outside of the hands become prominent. These are veins as they flow superficially. The veins are thin and less muscular. These carry the blood to the heart veins are placed superficially so they are easily visible to the eye and are prominent.
The blood in the veins will be carrying CO2 and will have many substances like sugar, amino acids, chemicals and bacteria.

Question 3.
Give the functions of lymph. Differentiate between Blood and the lymph.
Answer:
Functions of lymph are:

  1. Nutritive: It supplies nutrition and oxygen to those parts where blood cannot reach.
  2. Drainage: It drains away excess tissue fluid and metabolites and returns proteins to the blood from tissue spaces.
  3. Absorption: It absorbs the fats from the intestine through lymphatics.
  4. Defence: Lymphocytes and monocytes of the lymph function to protect the body. The lymphatics also remove bacteria from the tissues.

Difference between Blood and Lymph

Lymph Blood
1. It contains blood plasma without blood proteins and some RBC. 1. It contains blood plasms with proteins and all three types of blood cells namely RBC, WBC and blood platelets.
2. They are light yellow in colour and does not contain RBC and haemoglobin. 2. They are red in colour due to presence of haemoglobin in RBC,
3. It doesnot carry Oxygen. 3. It carries oxygen in the body.
4. It is the part of open circulatory system. 4. It is the part of closed circulatory system.

Question 4.
Name any two heart conditions that occur commonly. Briefly explain each of them.
Answer:

  1. Palpitations: Sometimes, one may experience the heart beating too hard or too fast or sometimes even skipping a beat. This can be frightening, but not serious or harmful and often this condition goes away on its own. Most of the time it is caused by stress or anxiety. Sometimes certain types of food may also cause palpitations.
    In rare cases, palpitations may be an indication of a more serious heart condition, specially if it is accompanied by shortness of breath, dizziness or chest pain.
  2. Hypertension: This is a condition that occurs in a person when blood flows through the blood vessels with a force greater than normal. This is also called High Blood Pressure. Hypertension can strain the heart, damage blood vessels and increase the risk of a heart attack or stroke.

Question 5.
During surgical operations or during accidents, the patient may be given blood from outside to save his life. What is the technical name of this process ? Briefly explain the precautions to be observed and taken in this process.
Answer:
During surgical operation or an accident when excess of bleeding takes place, the patient may be given blood from outside to save his life.
The transfer of blood from the donor to the recipient is called blood transfusion.
The following precautions are taken before the blood is given to the needy person:

  1. Matching of the donor’s blood with that of the recipient should be done.
  2. It should be made sure clinically that blood of donor is free from any infection.
  3. Sterilization of all the instruments to be used during the operation is must.

Question 6.
State briefly, the difference between white blood cells and the red blood cells.
Answer:
Difference between white blood cells and the red blood cells:

RBC WBC
1. They do not have nucleus at maturity. 1. They have a large characteristic nucleus.
2. They possess haemoglobin and are red. 2. They are colourless as they have no pigment.
3. They help in transport of respiratory gases. 3. They help in defence mechanism.
4. Life span is 120 days. 4. WBC have a short life span of 5 to 20 days.
5. They are about 5 million/mm3 of blood. 5. They are about 7000/ mm3 of blood.
6. In the embryonic stage the RBC are formed in the liver and spleen. But after birth, they are formed in the red bone marrow. 6. WBC are formed in the red bone marrow.

Question 7.
Answer very briefly, the following:
(a) Red Blood cells have no nucleus, then why do we call them cells?
(b) Why is it necessary to know The blood groups of the donor as well as the recipient ?
(c) Why should the blood going away from the stomach and intestines pass through the liver and not directly to heart?
Answer:
(a) RBC are formed in the liver and spleen when the organisjn is foetus. After birth these are formed in the red bone marrow. At the time of formation of RBC’s they have nucleus but later on they loose nucleus. Those enucleated cells perform all the functions of a cell so these are called cells.
RBC’s are surrounded by semipermeable plasma membrane. It contains homogenous cytoplasm and it is without the nucleus, endoplasmic reticulum, mitochondria, ribosomes and centrioles. RBC’s get advantage due to this condition. Corpuscles have more space to hold haemoglobin. It can as well give more oxygen by the haemoglobin to the tissue cells. So the enucleated condition is more useful to the tissue cells. The necessity of work has made them without nucleus and perform all the functions of the cells so they are called cells.

(b) Before transfusion of blood, it is most essential to determine the blood group of the donor and the recipient. The blood group of the donor and the recipient must match with each other, otherwise the RBC’s will stick to each other and thus the life of a recipient may be in danger as the blood groups are different. The sticking is due to the antigens (proteins) found in the blood of the donor and the antibodies found in the blood of the recipient.

(c) The blood from the stomach and the intestine goes to liver before going to the heart. Liver monitors the substances before passing into the body. Excess of glucose is retained by the liver in the form of glycogen and the excess amino acids are broken down by the liver. Harmful chemicals are detoxified and bacteria are destroyed and excess minerals, water and vitamins are stored in the liver.

Question 8.
Name the three kinds of blood vessels found in human beings. With the help of suitable diagrams, differentiate between them.
Answer:
The three kind of blood vessels found in human beings are arteries, veins and capillaries.

  1. Arteries are the blood vessels that carry blood from the heart to the various parts of the body.
  2. Veins are the blood vessels that carry blood from the body parts to the heart.
  3. Capillaries: These are the terminal branches of an artery, which rejoin to form a vein. A capillary is a very narrow tube whose walls have a single layer of cells with no muscles. Although the wall of a capillary is veiy thin, yet an exchange of nutrients, waste products and gases take place between the blood and the body fluids.Selina Concise Biology Class 8 ICSE Solutions – The Circulatory System 2

Differences:

Arteries

  1. Carry blood away from the heart.
  2. Have thick and more muscular walls.
  3. Carry oxygenated blood (except pulmonary artery which carries deoxygenated blood).
  4. The blood flows with jerks and under great force.

Veins

  1. Carry blood towards the heart.
  2. Have thin and less muscular walls.
  3. Carry deoxygenated blood (except pulmonary vein which carries oxygenated blood).
  4. The blood flows smoothly and under little pressure.

Capillaries:

  1. Arteries after entering an organ divide into number of smaller branches called arterioles which further divide repeatedly to form a network of fine branches called capillaries.
  2. The walls of the capillaries are very thin and are one cell deep.
  3. The Capillaries after the metabolic exchange unite to form larger vessels called venules, which again unite to form a vein.

Selina Concise Physics Class 7 ICSE Solutions – Sound

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Selina Concise Physics Class 7 ICSE Solutions – Sound

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Physics for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 7 Physics Chapter 6 Sound

  • Points to Remember
  •  Sound is a form of energy which produces the sensation of hearing.
  •  Sound requires a medium to travel. It cannot travel in vacuum.
  •  Sound travels in all directions. Sound can travel through solids, liquids and gases.
  •  Sound travels faster in solids than in liquids and gases.
  •  The loudness of sound is measured on a special scale called the decibel scale.
  •  Sound is classified into two groups. (i) Musical sound, (ii) Noise.
  •  Musical sound is produced by periodic vibrations.
  •  Noise is produced by non-periodic motions.
  •  What the sound gets repeated after reflection from a distant body, is called an echo.
  •  Multiple echoes are called reverberations.
  •  Sonar is method used to measure the depth of a sea and is based on the principle of echo.
  •  Music is pleasent to hear and is caused by periodic vibrations.
  •  Noise is irritating and is produced by an irregular pattern of waves.
  •  The three characteristics of sound are loudness, pitch, quality or timbre.
  •  Loudness depends upon many factors, e.g. amplitude, distance, waves of vibrating body, humidity, pressure, wind velocity etc.
  •  Pitch depends on the frequency of sound. Higher is the pitch, shriller is the sound.
  •  Loudness is merely a sensation.

Test Yourself

A. Objective Questions 

1. Write true or false for each statement

(a) Sound can travel in vacuum.
Answer. False.
Correct — Sound requires medium to travel.

(b) Sound is a form of energy.
Answer. True.

(c) Sound can only be produced by vibrating bodies.
Answer. True.

(d) Larger is the amplitude, feeble is the sound.
Answer.False.
Correct — Larger the amplitude, greater is the sound.

(e) The frequency is measured in hertz.
Answer. True.

(f) Loudness depends on frequency.
Answer. False.
Correct — Loudness depends on the amplitude.

(g) Waveforms of two different stringed instruments can be the same.
Answer. False.
Correct—Waveforms of two different stringed instruments cannot be the same.

(h) Female voice is shriller than the male voice.
Answer. True.

(i) A ticking clock sound is heard late when heard through a metal.
Answer. False.
Correct—A ticking clock sounds is heard early when heard through a metal.

2. Fill in the blanks

(a) Sound is produced when a body vibrates.
(b) The number of times a body vibrates in one second is called its frequency.
(c) The pitch of a sound depends on its frequency.
(d) Sound can travel in a medium solid, liquid or gas.
(e) We can hear sounds of frequency in the range of 20 Hz to 20,000 Hz.
(f) Sound requires a medium for propagation.
(g) Sound travels faster in solids than in liquids.
(h) The sound heard after reflection is echo.
(i) Sound produces sensation in ears.

3. Match the following

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 1

4. Select the correct alternative 

(a) We can distinguish a shrill sound from a flat sound by its

  1.  amplitude
  2.  loudness
  3.  pitch
  4.  none of the above.

(b) We can hear sound of frequency

  1.  10 Hz
  2.  500 Hz
  3.  100,000 Hz
  4.  50,000 Hz

(c) Sound cannot travel in

  1.  gases
  2.  liquids
  3.  solids
  4.  vacuum

(d) The minimum distance required between the source and the reflector so as to hear the echo in air is

  1.  10 m
  2. 17 m
  3.  34 m
  4.  50 m

(e) Wavelength is measured in

  1.  kg
  2.  second
  3.  litre
  4. metre

(f) The speed of sound in water is

  1.  332 m
  2. 1500 m
  3.  5000 m s
  4.  1000 m s

(g) Sound travels the fastest in

  1.  liquids
  2.  solids
  3.  gases
  4.  vacuum

B. Short/Long Answer Questions

Question 1.
What do you mean by a vibratory motion ?
Answer:
The oscillatory motion in which the body assumes a new shape during its motion, is called the vibratory motion.

Question 2.
What is sound ?
Answer:
Sound is a form of energy which produces the sensation of hearing.

Question 3.
How is sound produced ?
Answer:
Sound is produced by vibrating bodies.

Question 4.
Describe an experiment to show that each source of sound is a vibrating body.
Answer:
Sound is produced when a body vibrates. In other words, each source of sound is a vibrating body. This can be demonstrated by the following experiment.
Take a ruler. Press its one end on the table with the left hand as shown in figure. Pull down the other end of the ruler with the right hand and then leave it.
You will notice that the ruler vibrates i.e., the ruler moves to and fro and a humming sound is heard.
After some time, the ruler stops vibrating. No sound is then heard.

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 2
This shows that the humming sound is produced only because of the vibrations of the ruler.

Question 5.
Name two sources of sound.
Answer:
Each vibrating body is a source of sound. We, the human beings, produce sound when our vocal cords vibrate on blowing air through them by our lungs. Some animals like birds, frogs etc., also produce sound due to vibration of their vocal cords. But bees do not have the voice-boxes. They produce sound by moving their wings up and down very fast.

Question 6.
How do we produce sound ?
Answer:
Our throat has a larynx. The voice is produced in the larynx. Larynx is also called the voice box. It is designed to produce voice. It is a box like structure with walls of tough tissues. Inside two folds of the tissue, there is a gap. They are the vocal cords. When we breathe, the vocal cords become loose and the gap between them increases. When we talk, shout or sing, the cords become tight and hence they vibrate, thus produce sound. Given figure shows the part of the body which vibrates to produce sound.

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 3

Question 7.
The bees do not have voice-boxes. How do they produce sound ?
Answer:
The bees do not have the voice-boxes. Still they produce sound.
This happens by the vibrations produced by the quick movement of their wings. Bees buzz while flying and depositing pollen among flowers.

Question 8.
Can sound travel through a vacuum ? Describe an experiment to explain your answer.
Answer:
Experiment — Arrange an electric bell, a glass bell jar, a vacuum pump, a battery and a switch as shown in the figure. When the circuit is closed by pressing the switch, the bell starts ringing and sound can be heard. Now remove the air from the jar with the help of vacuum pump. The loudness of the sound gradually decreases and a stage comes when no sound is heard. Sound requires a medium to travel but cannot travel in vacuum.

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 4
Connect the bell to a battery through a switch. On pressing the switch, the bell starts ringing and a sound is heard. The sound reaches us through the air in the jar.
Now start the vacuum pump. It withdraws the air from the jar. You will notice that as the jar is evacuated, the sound becomes feeble and feeble. After some time when no air is left within the jar, no sound is heard. However, the hammer of the electric bell can be still seen striking the gong. The reason is that when no air is left in the jar, the sound does not reach us, although the bell is still ringing (or vibrating).
Thus, sound cannot travel through a vacuum.

Question 9.
Describe an experiment to show that sound can travel in water.
Answer:
Take a tub filled with water. Hold a bell in one hand and dip it in water. Keep one of your ears gently on the surface of water without letting water into the ear. Now ring the bell inside water. You will be able to hear the sound clearly. This shows that sound can travel through liquids.

Question 10.
Describe an experiment to show that sound can travel in a solid.
Answer:
Take two empty ice-cream cups. Make a small hole at the bottom of each cup and pass a long thread (about 20 m long) through them. Tie a knot or match-stick at each end of the thread so that the thread does not slip out through the holes. This makes a toy – telephone

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 5
Now use the toy-telephone as shown in figure and talk to your friend. You will be able to hear the sound of your friend. This shows that sound travels through the thread and reaches your ear. Thus, sound can travel through a solid.

Question 11.
Can two person hear each other on moon’s surface ? Give reason to support your answer.
Answer:
No, we cannot hear each other since sound requires medium for transmission. It cannot travel through vacuum.

Question 12.
What is a longitudinal wave ?
Answer:
In a longitudinal wave, the particles of air vibrate to and fro about their mean positions in the direction of travel of sound.

Question 13.
Define the following terms :
Amplitude, Time period, Frequency.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 6
(a) Amplitude (A) : The maximum displacement of a wave on either side of its mean position is called Amplitude. A = XY is amplitude.
(b) Time Period (T) : Time taken to complete one vibration is called Time Period, i.e. from A to B

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 7
(c) Frequency (f) or u
Number of oscillations made by a wave in one second is known as its frequency.

Question 14.
Write the audible range of frequency for the normal human ear.
Answer:
The range of frequency from 20 Hz to 20,000 Hz is called the audible range for the normal human ear.

Question 15.
What are ultrasonics ? Can you hear the ultrasonic sound ?
Answer:
Sounds of frequency higher than 20,000 Hz are called the ultrasonics. We cannot hear the ultrasonic sounds.

Question 16.
What are infrasonics ? Can you hear them ?
Answer:
Sounds of frequency lower than 20 Hz are called the infrasonics. We cannot hear the infrasonic sounds.

Question 17.
How does a bat make use of ultrasonics waves to find its way?
Answer:
Use of ultrasonics by bats : Bats have no eyes. But they easily move about without colliding with any object (or obstacle). The reason is that they produce ultrasonic sound as they fly. When this ultrasonic sound comes back after reflection from any object (or obstacle) in their way, they hear it and thus they detect the presence of the object (or obstacle).

Question 18.
Name the two characteristics of sound which differentiate two sounds from each other.
Answer:
A sound wave is characterized by its amplitude and frequency. Depending upon the (amplitude and frequency of the sound wave, the following two characteristics of sound :
(1) Loudness, and (2) Pitch.

Question 19.
On what factor does the loudness of a sound depend ?
Answer:
The loudness of a sound depends on the amplitude of vibration of the vibrating body producing the sound.

Question 20.
How does the loudness of sound produced depend on the vibrating area of the body ?
Answer:
The loudness of sound also depends on the area of the vibrating body. Greater the area of the vibrating body, louder is the sound produced.
If you take two drums, one small and the other big, and beat both of them to produce vibrations in them, We will notice that the sound produced from the big drum is louder than that produced from the small drum. In temples, you must have noticed that the bell with a big case produces a louder sound than that with a small case.

Question 21.
The outer case of the bell in a temple is made big. Give a reason.
Answer:
The outer case of the bell in a temple is made big. So that there is multiple reflection of sound and the sound can be amplified.

Question 22.
State the factors on which the pitch of a sound depends.
Answer:
The pitch of a sound depends on its frequency (i.c., on the frequency of the vibrating body).

Question 23.
Differentiate between a high pitch sound and a low pitch sound.
Answer:
Higher the pitch, the shriller is the sound. Lower the pitch, the flat (or grave) is the sound.

Question 24.
How does a man’s voice differ from a woman’s voice ?
Answer:
A female voice is shriller than a male voice because of higher frequency. Higher is the frequency, shriller is the sound. Female has higher frequency.

Question 25.
Name the characteristic which differentiates two sounds of the same pitch and same loudness.
Answer:
The quality is the characteristic of sound which distinguishes the two sounds of the same pitch and same loudness.

Question 26.
You recognize your friend by hearing his voice on a telephone. Explain.
Answer:
We can recognize our friend by hearing his voice on a telephone due to quality of sound and pitch of sound.

Question 27.
A musician recognizes the musical instrument by hearing the sound produced by it, even without seeing the instrument. Which characteristic of sound makes this possible ?
Answer:
It is the pitch and quality that helps a musician recognize the musical instrument by hearing the sound produced by it, even without seeing the instrument.

Question 28.
Describe an experiment to show the production of sound having low and high pitch.
Answer:
Take few rubber bands some thicker and longer, few thinner and of shorter length. Cut and stretch these rubber bands by holding one end of the string in your mouth under the teeth and the other end in your hand. Now pluck these rubber bands one by one. The rubber bands thicker and longer will produce sound with a lower pitch. The rubber bands thinner and shorter will produce sound with a higher pitch.

Question 29.
How does a musician playing on a flute change the pitch of sound produced by it ?
Answer:
In musical instruments like flute and clarinet, the pitch of sound is changed by changing the length of vibrating air column when different holes in it are closed.

Question 30.
Why are musical instruments provided with more than one string ?
Answer:
The stringed instruments are provided with a number of strings of different thickness and under different tensions so that each string produces sound of a different pitch.

Question 31.
How can the pitch of sound produced in a piano be changed ?
Answer:
In a piano, the string is struck to make the string vibrate and produce sound. The pitch of sound produced can be changed by stretching or loosening the strings of piano.

Question 32.
Explain why you can predict the arrival of a train by placing your ear on the rails without seeing it.
Answer:
The sound produced by the moving wheels of train travels much faster through the track than through the air. Therefore they hear through the track much before it is heard through the – air.

Question 33.
Write the approximate speed of sound in (i) air, (ii) water and (iii) steel.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 8

Question 34.
During a thunderstorm, the sound of a thunder is heard after the lightning is seen. Why ?
Answer:
The velocity of light is 3 × 108 m/s whereas velocity of sound is 332 m/s. First we see the flash of light and then we hear the thunder.

Question 35.
Describe an experiment to estimate the speed of sound in air.
Answer:
To estimate the speed of sound in air suppose we choose two  hills A and B about a kilometer apart. A person at the hill A fires  a gun. Another person at the hill B starts a stop watch as he sees the flash of the fire and stops it on hearing the sound. Thus, he measures the time interval between the seeing of flash and hearing of the sound. Let it be t second. Then measure the distance between the hills A and B. Let it be S metre.

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 9
Experimentally, it is found that the speed of sound in air is nearly 330 m s-1

Question 36.
Can sound travel through solids and liquids ? In which of these two does it travel faster ?
Answer:
Sound travels with highest speed in — solids.
and Sound travels with lowest speed in — gases.

Question 37.
What do you mean by reflection of sound ?
Answer:
Reflection of Sound— When a sound wave strikes a rigid surface, it retraces from its path is called reflection of sound.

Question 38.
State one use of reflection of sound.
Answer:
The reflection of sound is used in making the speaking tube (or megaphone), sound board and trumpet.

Question 39.
What is echo ?
Answer:
Echo is the sound heard after reflection from a rigid surface such as a cliff, a hillside, the wall of a building etc.

Question 40.
What minimum distance is required between the source of sound and the reflecting surface to hear an echo ? Give reason.
Answer:
Since sound has to travel an equal distance in going up to the reflecting surface and in coming back from the reflecting surface, therefore it must travel nearly 33/2 = 16.5 m either way. Thus, to hear the echo clearly in air, the reflecting surface should be at a minimum distance of 16.5 m from the source of sound.

Question 41.
List four substances which are good absorbers of sound.
Answer:
When sound falls on sofa, fluffs and light substances such as clothes, papers, thermocol, coating of plaster of paris, carpets, curtains, furniture, wood etc., they absorb the sound to a good extent. These are called good absorbers of sound.

Question 42.
List the measures that you will take when designing a sound-proof room.
Answer:
In order to design such a sound proof room we take the following measures
(1) The roof of the enclosure must be covered by plaster of paris after putting the sheets of thermocol.
(2) The walls of the enclosure should be covered by the wooden strips.
(3) The floor must be laid down by thick carpets.
(4) The machine parts of all the electrical equipments such as fan, air conditioner etc. must be placed outside the enclosure.
(5) Thick curtains should be used to cover the doors and keep them closed.
(6) Thick stripping must be used to cover the openings of doors and windows.

C. Numericals

Question 1.
A boy fires a gun and another boy at a distance of 1020 m hears the sound of firing the gun 3 s after seeing its smoke. Find the speed of sound.
Answer:

Selina Concise Physics Class 7 ICSE Solutions Chapter 6 Sound 10

Question 2.
A boy on a hill A fires a gun. The other boy on hill B hears the sound after 4 s. If the speed of sound is 330 ms-1, find the distance between the two hills.
Answer:
Speed, v = 330 ms-1
t = 4s
Distances = v × t
= 330 × 4s = 1320 m Ans.

Selina Concise Physics Class 7 ICSE Solutions – Energy

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Selina Concise Physics Class 7 ICSE Solutions – Energy

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 7 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 7 with Free PDF download option. Selina Publishers Concise Physics for Class 7 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 7 Physics ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 7 Physics Chapter 3 Energy

  • Points to Remember
  •  Work is said to be done if the applied force on the body moves it. If no motion takes place, no work is said to be done.
  •  The amount of work done depends on two factors : (i) on the magnitude of the force applied (greater the force applied, greater is the work done), and (ii) on the distance moved in the direction of force (greater the distance moved, greater is the work done).
  •  The work done by a force on a body is equal to the product of the force and the distance moved by the body in the direction of force, i.e. Work done = Force × distance moved in the direction of force Or W = F × d
  •  The S.I. unit of work is joule (J), where 1 joule (J) = 1 newton (N) × 1 metre (m)
  •  The energy of a body is its capacity (or ability) to do work. The energy of a body in a state is equal to the work done on the body to bring it to that state.
  •  The S.I. unit of energy is joule (J).
  •  Kinetic energy of a body is the energy possessed by it due to its motion. It is the energy stored when work is done to bring the body in motion.
  •  Kinetic energy of a moving body depends on two factors :
    (i) on the mass of the body (greater the mass of the body, greater is its kinetic energy), and (iii) on the speed of the body (more the speed of the body, higher is its kinetic energy).
  •  The potential energy changes into the kinetic energy when it is put to use.
  •  In transformation of energy, the total sum of useful and non-useful energy obtained after conversion is equal to the energy converted, i.e. the total energy remains conserved.
  •  According to the conservation of mechanical energy, if friction is neglected, the total sum of potential energy and kinetic energy remains constant. Examples are : motion of roller coaster, free vertical fall of a body etc.
  •  The electricity obtained from the energy possessed by the flowing water is called the hydro-electricity.

Test Yourself

A. Objective Questions 

1. Write true or false for each statement

(a) A man going up has potential energy and kinetic energy both.
Answer. True.

(b) A gum bottle lying on a table has no energy.
Answer. False.
Correct — A gum bottle lying on a table has energy.

(c) In an electric fan, electrical energy changes into the mechanical energy.
Answer. True.

(d) Potential energy changes into kinetic energy when it is put to use.
Answer. True.

(e) One form of energy cannot be converted into another form.
Answer. False.
Correct — One form of energy can be converted into the other form.

(f) There is always some loss of energy in conversion from one form of energy to another form, so the total energy is not conserved.
Answer. False.
Correct — There is always some loss of energy in conversion from one form of energy to the other form, so the total energy is conserved.

(g) The energy of flowing water can be converted into electric energy (electricity).
Answer. True.

2. Fill in the blanks

(a) An electric fan converts electrical energy into mechanical energy.
(b) Cooking gas converts chemical energy into heat energy.
(c) Energy possessed by a compressed spring is potential energy.
(d) The ability to do work is called energy
(e) The energy possessed by a body due to its position is called potential energy.
(f) The energy possessed by a body due to its motion is called kinetic energy.
(g) Green plants convert light energy into chemical energy.
(h) The S.I.unit of energy is joule
(i) An object falling freely from the roof of a multistory building has potential energy and kinetic energy when halfway down the building.

3. Match the following columns

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 1

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 2

4. Select the correct alternatives 

(a) When we rub our hands

  1.  kinetic energy changes into potential energy
  2.  mechanical energy changes into heat energy
  3.  potential energy changes into kinetic energy
  4.  heat energy changes into mechanical energy.

(b) A ball rolling on the ground possesses

  1.  kinetic energy
  2.  potential energy
  3.  no energy
  4.  heat energy

(c) The energy stored in an electric cell is

  1.  chemical energy
  2.  electrical energy
  3.  heat energy
  4.  mechanical energy.

(d) When a bulb lights up on passing current, the change of energy is

  1.  from electrical energy to heat energy
  2.  from electrical energy to light energy
  3.  from electrical energy to heat and light energy
  4.  from electrical energy to mechanical energy.

(e) The correct statement is

  1.  Both work and energy have the same units
  2.  Potential energy of a body is due to its motion
  3.  Kinetic energy of a body is due to its position or state
  4.  Kinetic energy can change into potential energy, but potential energy cannot change into kinetic energy.

(f) According to law of conservation of energy, energy changes from one form to another form, but the total energy of that system

  1.  increases
  2.  decreases
  3.  alternates
  4.  remains the same

B. Short/Long Answer Questions

Question 1.
Define the term energy.
Answer:
Energy is the capacity of doing work.

Question 2.
State the unit of energy and define it.
Answer:
The energy is measured in the same unit as work. Therefore the S.I. unit of energy is joule (symbol J).
A body is said to possess an energy of one joule if a force of 1 newton moves the body by a distance of 1 metre in the direction of force.
Another unit of energy is calorie (symbol cal) where 1 cal = 4.2 J. A bigger unit is kilo-calorie (symbol kcal) where 1 kcal = 1000 cal.

Question 3.
Name five different forms of energy.
Answer:
The different forms of energy are :
(i) Mechanical energy
(ii) Heat energy
(iii) Light energy
(iv) Chemical energy
(v) Sound energy
(vi) Magnetic energy
(vii) Electrical energy and
(viii) Atomic energy or nuclear energy.

Question 4.
What are the two kinds of mechanical energy.
Answer:
The mechanical energy is found in two forms namely :
(a) The potential energy, and (b) The kinetic energy.

Question 5.
What is potential energy ? State its unit.
Answer:
The energy of a body at rest is called the potential energy. It is defined as follows :
Potential energy of a body is the energy possessed by it due to its state of rest or position. Actually, it is the work spent in bringing the body to that state of rest or position.
It is written as P.E. or U.
The S.I. unit of potential energy is Joules.

Question 6.
Give one example of a body that has potential energy, in each of the following : (i) due to its position, (ii) due to its state.
Answer:
(i) Potential energy of a body is the energy possessed by it due to its state of rest or position. It is the energy stored when work is done on the body to bring it to that state or position.
(ii) Potential energy of a body in the raised (or lifted) position depends on two factors : (1) the mass of the body greater the mass of the body, greater is the potential energy of the body), and (2) the height of the body above the ground (greater the height of the body, greater is its potential energy.)

Question 7.
State two factors on which the potential energy of a body at a certain height above the ground depends.
Answer:
The potential energy of a body in the raised position depends upon the following two factors :
(a) The mass of the body: Greater the mass of the body, greater is the potential energy of the body.
(b) Its height above the ground : Higher the height of the body, greater is its potential.

Question 8.
Two bodies A and B of masses 10 kg and 20 kg respectively are at the same height above the ground. Which of the two has the greater potential energy ?
Answer:
The body B having mass 20 kg has the greater potential energy. This can be explained as follows :
P.E. = mgh .
For both the bodies gravity and height are same so the body with greater mass possesses greater potential energy.

Question 9.
A bucket full of water .is on the first floor of your house and another identical bucket with same quantity of water is kept on the second floor. Which of the two has greater potential energy ?
Answer:
A bucket full of water kept on second floor has the greater potential energy. This can be explained as follows :
P.E. = mgh
Mass of both bucket and the gravitational force are same, so the body at greater height will possess more potential energy.

Question 10.
Define the term kinetic energy. Give one example of a body which possesses kinetic energy.
Answer:
The energy of a body in motion is called its kinetic energy. It is defined as follows :
Kinetic energy of a body is the energy possessed by it due to its state of motion.
Actually, it is the work done on the body bringing it to the state of motion. In short form it is written as K.E. or K.
Example : In a swinging pendulum moving to and fro, the bob has the kinetic energy.

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 3

Question 11.
State two factors on which the kinetic energy of a moving body depends.
Answer:
The kinetic energy of a moving body depends on the following two factors :
(a) The mass of the body — Greater the mass of the body, higher is its kinetic energy.
(b) The speed of the body — More the speed of the body, higher is its kinetic energy.

Question 12.
Two toy-cars A and B of masses 500 g and 200 g respectively are moving with the same speed. Which of the two has the greater kinetic energy?
Answer:
The toy car ‘A’ of mass ‘500 gm’ has the greater kinetic energy. This can be explained as :
K.E. = 1 / 2 Mv2
Here, both the cars are moving with same speed. So the car with greater mass will possess greater kinetic energy.

Question 13.
A cyclist doubles his speed. How will his kinetic energy change: increase, decrease or remain same ?
Answer:
When a cyclist doubles his speed. His kinetic energy increases four times.
K.E. = 1 / 2 Mv2
When v = doubles the K.E. quadriples

Question 14.
Name the form of energy which a wound up watch spring possess.
Answer:
A wound up watch spring has the potential energy because of its wound up state. As the spring unwinds itself, the potential energy changes into the kinetic energy. This kinetic energy does work in moving the arms of the watch

Question 15.
Can a body possess energy even when it is not in motion ? Explain your answer with an example.
Answer:
Yes, a body possesses energy even when it is not in motion ;
Consider a body raised to a certain height say h. It its velocity is zero. Kinetic energy will be zero but the body will have.
P.E. = mgh
Thus, a body may possess energy even though it is not in motion.

Question 16.
Name the type of energy (kinetic or potential) possessed by the following :
(i) A moving cricket ball.
(ii) A stone at rest on the top of a building.
(iii) A compressed spring.
(iv) A moving bus.
(v) A bullet fired from a gun.
(vi) Water flowing in a river.
(vii) A stretched rubber band.
Answer:
(i) Kinetic energy.
(ii) Potential energy.
(iii) Potential energy.
(iv) Kinetic energy.
(v) Kinetic energy.
(vi) Potential energy.
(vii) Potential energy.

Question 17.
Give one example to show the conversion of potential energy to kinetic energy when put in use.
Answer:
The example to show the conversion of potential energy to kinetic energy when put in use is :
A stone at a height has the potential energy due to its lifted or raised position. In the figure below when the stone is dropped from that position, it begins to fall. The falling stone has the kinetic energy. Thus, the potential energy stored in the stone in its raised position changes into the kinetic energy when the stone is falling. This kinetic energy does work on the nail as the stone strikes the nail arid makes the nail to move into the wood.

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 4
Similarly, in the figure below the potential energy possessed by the stone at a height changes into its kinetic energy when it falls, The kinetic energy of the falling stone does work in raising the weight upwards.

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 5

Question 18.
State the energy changes that occur in the following :
(i) The unwinding of a watch spring.
(ii) Burning coal while operating a steam engine.
(iii) Lighting of a torch bulb.
(iv) An electric generator (or dynamo).
Answer:
(i) Potential energy to kinetic energy.
(ii) Chemical energy of coal changes to heat energy of the steam. Heat energy changes into mechanical energy.
(iii) Chemical energy into light and heat energy.
(iv) Electrical energy change into mechanical energy.

Question 19.
Energy can exist in several forms and may change from one form to another. Give two examples to show the conversion of energy from one form to another.
Answer:
The examples that show the conversion of energy from one form to another are :
(1) In a steam engine, the chemical energy of the coal first changes into the heat energy of the steam. Then heat jenergy of steam changes into the mechanical energy which makes the train to move.
(2) In an electric motor (or in fan), the electrical energy changes into the mechanical energy. This energy rotates the axle of motor (or the blades of the fan).

Question 20.
Give one relevant example for each of the following transformation of energy :
(i) Electrical energy to heat energy.
(ii) Electrical energy to mechanical energy.
(iii) Electrical energy to light energy.
(iv) Chemical energy to heat energy.
(v) Chemical energy to light energy.
Answer:
(i) In an electric heater, oven, geyser, toaster etc., the electrical energy changes into heat energy.
(ii) An electric generator.
(iii) Tube eight of bulbs.
(iv) Burning of wood, coal etc.
(v) Fire crackers burst

Question 21.
What do you mean by conservation of mechanical energy? State the condition when does it hold.
Answer:
This means “The total MECHANICAL ENERGY (P.E + K.E) of an isolated system at any instant is equal to the sum of kinetic ENERGY and the potential ENERGY.”
Condition : Condition under which the mechanical energy is conserved is “WHEN THERE ARE NO FRICTIONAL FORCES.” In other words the mechanical energy is conserved strictly in vacuum where friction due to air is absent.

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 6

Question 22.
Give one example to show that the sum of potential energy and kinetic energy remains constant if friction is ignored.
Answer:
During the vertical fall of ball, if friction due to air is neglected, the total sum of potential energy and kinetic energy at each point of its path remains same.

Question 23.
A ball is made to fall freely from a height. State the kind/ kinds of energy possessed by the ball when it is
(a) at the highest point
(b) just in the middle
(c) at the ground.
Answer:
(a) Potential energy.
(b) Potential energy + Kinetic energy.
(c) Kinetic energy.

Question 24.
State the changes in form of energy while producing hydro electricity.
Answer:
The water in motion in a river or sea has the kinetic energy. The energy possessed by the flowing water is called the hydro energy. The most important use of hydro energy is to produce electricity from it.

Selina Concise Physics Class 7 ICSE Solutions Chapter 3 Energy 7
Figure shows the principle of a hydroelectric power plant. The flowing water of river is collected in a dam at a high altitude. The water stored in the dam has the potential energy. When water from dam falls on the water turbine, the potential energy of the water stored in dam changes into its kinetic energy and this kinetic energy of water is transferred to the blades of turbine as the kinetic energy which rotates the turbine. As the turbine rotates, it rotates the armature of the generator (or dynamo) to produce electricity.

 

 

Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants

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Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 2 Reproduction in Plants. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 2 Reproduction in Plants

REVIEW QUESTIONS

Multiple Choice Questions:

1. Put a tick mark (✓) against the correct alternative in the following statements

(a) Pollen is produced in the:

  1. Filament
  2. Style
  3. Pistil
  4. Anther

(b) Reproductive whorls of a flower are:

  1. Stamens and carpels
  2. Sepals and petals
  3. Sepals and stamens
  4. Petals and carpels

(c) Grafting is a method of:

  1. Artificial vegetative propagation
  2. Sexual reproduction
  3. Artificial pollination
  4. Cross-pollination

(d) Which one of the following is a false fruit ?

  1. Tomato
  2. Apple
  3. Potato
  4. Pea

Short Answer Questions:

Question 1.
Write two ways in which pollination may occur in plants.
Answer:
The two ways in which pollination may occur in plants are:
(a) Self-pollination.
(b) Cross-pollination.

Question 2.
Name the three agents of pollination.
Answer:
The three agents of pollination are:
(a) Insect
(b) Wind
(c) Water

Question 3.
Give two features of flowers which favour pollination by insects.
Answer:
Specialities of insect-pollinated flowers:
(a) These flowers are large with coloured petals to attract insects.
(b) These are scented so that insects locate the flowers by smell.

Question 4.
Name two characteristics of flowers in which pollination occur by wind.
Answer:
Special features of wind-pollinated flowers:
(a) They produce light pollen so that it is easily carried away.
(b) They produce a large quantity of pollen.

Question 5.
What is a “false fruit” ? Give one example:
Answer:
In false fruits the base of the flowers (thalamus) becomes the main fleshy part of the fruit, while the ovary remains a small central part containing seeds. Example: Apple and Pear.

Question 6.
Name any three agencies for dispersal of seeds.
Answer:
a. Wind
b. Water
c. Man and animals, birds, bats, squirrels.

Question 7.
Fill in the blanks by selecting suitable words:
(unisexual, fertilisation, fruit, stamen, anther, bisexual, pollination, seed, ovary)
Answer:
a. A flower that bears both the male and the female parts is known as bisexual flower.
b. A flower bearing only male or female parts is known as unisexual flower.
c. Transfer of pollen grains from the anther to the stigma is known as pollination.
d. Fusion of male cell with the female cell is called fertilisation.
e. The ovule develops into a seed.
f. The ovary of the flower develops into a fruit.

Long Answer Questions:

Question 1.
What is vegetative reproduction?
Answer:
Vegetative reproduction: In this method, new plants are produced by the vegetative parts of the plants. The vegetative part mean the leaf, stem and root. Potato, mint, ginger, banana etc. are reproduced by this method.
Vegetative propagation can occur by natural methods as well as by artificial methods.
Natural method includes reproduction by stem, by roots and by leaves.
Artificial method include reproduction by cutting, layering, grafting and tissue culture.

Question 2.
Briefly explain why a gardener prefers to grow certain plants vegetatively?
Answer:
Gardener prefer to grow certain plants by vegetative method. The advantages in doing so are as follows:

  1. Reproduction by vegetative parts takes place in a shorter time.
  2. New plants, thus produced, spread very fast in a small area.
  3. It is a surer method.
  4. All the characters of the mother plant are retained by the daughter plants.

Question 3.
Why is it disadvantageous to grow plants vegetatively?
Answer:
It is disadvantageous to grow plants vegetatively because of following:

  1. As all plants developed by vegetative propagation are identical, they are likely to be affected simultaneously if a disease spreads in the farm.
  2. Dispersal of plants does not take place on its own. Daughter plants, so developed, tend to remain nearby and are restricted to a particular area leading to competition for resources.

Question 4.
What is meant by pollination? Explain the structure of germinating pollen grain with the help of a labelled diagram.
Answer:
Pollination: Pollination is the process in which the pollen grains from the anthers are transferred to the stigma.
Structure of the pollen grain: After pollination pollen grains are deposited on the stigma of the carpel. Under suitable conditions pollen grains produce a tube known as pollen tube. This tube grows down through the stigma and style towards the ovary.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 1
The nucleus of the pollen grains divides by mitosis and forms two male gametes. The tip of the pollen tube after entering ovary discharges the two male gametes into the embryo sac.
One of the male gametes fuses with the egg to form the zygote. This fusion is called fertilization. Another male gamete fuses with the diploid secondary nucleus and forms the endosperm, a food storing tissue.

Question 5.
Imagine all the seeds produced by a plant happen to fall under the same plant and sprout into new plants. Mention any two problems that will be faced by the new plants. –
Answer:
If all the seeds produced by a plant happen to fall under the same plant and sprout into new plants then in this situation plants will face the following problems:

  1. A large number of plants will grow in a small limited space. The water and the minerals available to them in the soil will be limited.
  2. The air surrounding them will not be enough and less sunshine will be available to them. As a result, most of these sprouted plants will die.

Question 6.
What is a flower ? Draw a neat labelled diagram showing the L.S. of a typical flower.
Answer:
A flower is a reproductive part of a plant. It helps in sexual reproduction as it has male parts and female parts. A fully opened flower has the following parts:
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 2

Stalk—A flower is attached to the shoot by means of stalk or pedicel stalk. The tip of the stalk is swollen or flattened. This is called torus or thalamus or receptacle.
The different parts of a flower are inserted on the thalamus. There are usually four whorls as

Calyx (Sepals)
Corolla (Petals)
Androecium (stamens)
Gynoecium (Carpels) Present on the thalamus

  1. Sepals (Calyx): These are the outermost part of the flower. These are leaf like and green in colour. This is the outer covering of the flower and form outer whorl in a flower. The Calyx (sepals) enclose the inner parts of the flower when it is a bud. It is protective in function.
  2. Corolla (Petals): Petals form the second whorl inner to the sepals. These are usually coloured, gaudy, or white in colour and scented and give sweet smell. The value of a flower is due to the attractive colour of the petals. These attract the insects for pollination.
  3. Stamens (Androecium): The third whorls inner to the petals are stamens. This third whorl is called Androecium. These are the male parts of the flower. Each stamen is formed of a long narrow, hair like structure called filament. On its tip it bears, a rounded broad sac like structure called anther. Each anther has two anther lobes. Each anther lobe has two pollen sacs which have powdery mass called pollen grains.
  4. Carpels (Gynoecium): Carpels are the inner most or fourth whorl in a flower. It is lodged on the thalamus and forms the female part of a flower. This whorl of carpels is called gynoecium. Each carpel or pistil has three parts.
    (a) The lower most, swollen part is ovary. It is attached to the thalamus.
    (b) The middle part is style which is narrow, thread like.
    (c) Stigma: The style ends in a knob like, rounded structure which is sticky in nature to receive the pollen grains.
    The ovaries contain ovules which later turn into seeds after fertilization and the ovary wall forms the fruit sometimes the thalamus also becomes a part of the fruit as in apple.

Question 7.
Write short notes on the following:
(a) Micro propagation
(b) Bryophyllum
(c) Vegetative reproduction
(d) Grafting
Answer:
(a) Micro propagation: This is the propagation of plants involving cell and tissue culture. If vegetative propagation is not possible in a crop, then buds, shoot apex or any other part of the plant can be used as explant for micropropagation.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 3

  1. The explants are treated with sterilisation chemicals to prevent microbial growth, and then cultured in a particular nutrient medium.
  2. Cells grow and divide to form a cell mass called callus Some growth regulators (Plant hormones) are added.
  3. The callus differentiates into plant parts looking like plant (plantlet). After 4-6 weeks the plantlets transferred to the soil.

(b) Bryophyllum: It is a beautiful plant grown in gar xerophyte plant and can grow in any type soil or container. It requires sun and watering time to time. We can grow it vegetatively.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 4
When a leaf is put on the soil or falls off accidentally from the parent plant. It starts giving out buds in the notches of the leaves. These buds start growing when in touch with soil having moisture. They give out adventitious roots which go into the soil and small aerial shoots which go into the air. So these adventitious buds form many plants from a single plant. Thus we can get many plants from a single leaf. We can grow these tiny plants into separate pots to get independent plants. This is one of the vegetative mode of reproduction.

(c) Vegetative reproduction: This is method of producing new plants from the vegetative parts of the plants. The vegetative part means the leaf, stem, root. As potato, mint, ginger, banana, sugar beet, gul-e-daudi, asparagus, sugar cane, are produced by this method.

(d) Grafting: In plants like mango, zizyphus (ber), guava apples, fruits, roses, a small bud is fixed on the stem. Many types of apples on a single plant thus a small orchard on a single plant. So we can have different types of roses and chrysanthemums on a single plant.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 5

Question 8.
How artificial pollination is useful to plant breeders ? Discuss briefly.
Answer:
Artificial pollination means transfer of pollen to the stigma artificially. In ancient times, it was a common practice to sprinkle “male flowers of palms on the “female flowers”. However, in modem era, plant breeders use artificial pollination for developing new varieties. The breeders remove the anthers in young flowers and cover such flowers by plastic bags. Such flowers are then pollinated with pollen from the plants of the desired variety.

Question 9.
With the help of suitable diagrams, describe
(a) Binary fission in plants
(b) Budding in yeast cell
Answer:
(a) Binary fission: This is one of the asexual mean of reproduction. In lower plants like bacteria reproduction takes place by this process. In this process the nucleus of the cell divides into two. Then the cell wall splits across the middle of the cell. Thus each part has a nucleus. Thus each part is an independent bacterium.Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 6
Later on these two parts of the cell get separated from each other and form two independent individuals called daughter cells and lead independent life.

(b) Budding in yeast cell: Budding is the most common method in yeast. The Parent cell produces an outgrowth called a bud. The bud grows, and then gets detached from the parent body to lead an independent life.
Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Plants 7

Selina Concise Chemistry Class 6 ICSE Solutions – Water

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Selina Concise Chemistry Class 6 ICSE Solutions – Water

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Chemistry. You can download the Selina Concise Chemistry ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Chemistry for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina Concise ICSE Solutions for Class 6 Chemistry Chapter  7  Water

POINTS TO REMEMBER

  1. Water cannot be replanished and without water we cannot live.
  2. 4 / 5 th of earth’s surface is covered with water and 1% of this available water is in the form of rivers, lakes, ponds and under ground water. It is utilized for agriculture and living beings consumption.
  3. In the atmosphere water is present in the form of vapour, mist, clouds etc.
    Selina Concise Chemistry Class 6 ICSE Solutions Chapter 7 Water 1
  4. Distillation : The process of removal of the dissolved salts from sea/ocean water.
  5. Purest form of water is rain water as it is formed by evaporation and condensation.
  6. Sea water is unfit for agriculture as plants do not tolerate saline water.
  7. Change of water from water bodies (lakes, rivers and oceans) into vapours in air and condensing of vapours and fall in the form of snow, water is called water cycle and water cycle plays an important role in
    (i) restoring the lost water from earth’s surface
    (ii) in controlling the climatic conditions.
  8. Water vapour is one of the invisible gases which makes up the air we breathe.
  9. Drinking water may contain some minerals and salts but it must be free from suspended impurities, harmful bacteria and germs.
  10. Sometimes water from a source look clear but may contain germs which cause water borne diseases like typhoid, cholera, jaundice, dysentry, gastroenteritis etc.
  11. Water can be made fit for drinking by
    (i) boiling,
    (ii) sterilisation
    (iii) exposing to air and sunlight
    (iv) by chemical treatment like chlorination or ozonisation.
  12. Water is universal solvent i.e. water can dissolve nearly in every substance.
  13. Distilled water is the purest form of water but not good for drinking purposes. It is good for medicinal purposes, laboratories and batteries.
  14. Both stirring and heating help in dissolving the substance in water.
  15. “The amount of solute that dissolves in a given quantity of solvent at a given temperature is called solubility of the solute.”
  16. Air dissolved in water helps aquatic animals and plants to survive.
  17. Eutrophication : “The deficiency of oxygen in the water may cause death of aquatic animals. This loss of dissolved oxygen from water in water bodies is called eutrophication.”

EXERCISE-I

Question 1.
Name:

(a) Three major sources of natural water
(b) Four sources of surface water.
(c) Two underground sources of water.

Answer:

(a) Three major sources of natural water :

  1. Surface water (sea water)
  2. Above surface water (rain)
  3. Underground water (springs)

(b) Four sources of surface water sources :

  1. Ocean water
  2. River water
  3. Lake water
  4. Glaciers

(c) Two sources of underground water :

  1. Well water
  2. Spring water

Question 2.
Answer the following questions in short:

(a) In which form is water present in the atmosphere ?
(b) Which source of water contains the highest concentration of salt in it ?
(c) Why is rain water considered the purest form of natural water?
(d) What possible impurities does rain water contain ?
(e) What is water table ?
(f) Why is spring water pure enough for drinking but unsuitable for laboratory use ?
(g) Why the taste of spring water differs at different places ?

Answer:

(a) Water is present in the form of water vapours in the atmosphere.
(b) Sea water contains highest concentration of salt.
(c) Rain water is the purest form of water as it is distilled water i.e. water from surface of earth has evaporated and then vapours condense in the atmosphere.
(d) The impurities present in rain water are dust and dissolved gases like oxygen, nitrogen and carbon dioxide and these gases are not poisonous, rain water is safe for drinking.
(e) Level of ground water is called water table.
(f) Spring water is free from suspended impurities and germs (harmful bacteria) as water has been filtered through different layers of soil and is fit for drinking. Spring water contains dissolved impurities which are due to the nature of soil surrounding the spring and cannot be used for laboratory purposes, where distilled water free from impurities is needed.
(g) Spring water contains unsolved impurities which have entered the water from surrounding soil and soil impurities (salts) differ from place to place. Hence taste of water differs from place to place.

Question 3.
List three major impurities present in river water.
Answer:
Three major impurities present in river water :

  1. Suspended impurities like clay and sand particles.
  2. Harmful bacteria.
  3. Mineral salts.

Question 4.
Give the percentage of water in the following :

(a) Rice and wheat grains
(b) Eggs
(c) Tomatoes
(d) Bread
(e) Water melon

Answer:
Percentage of water in :

(a) Rice — 3 % to 4% Wheat grain — 3% to 4%
(b) Eggs —75%
(c) Tomatoes — 95%
(d) Bread —25%
(e) Water melon — 97%

Question 5.
What are the three states of water ?
Answer:
Three states of water are :

  1. Ice (solid)
  2. Liquid (water)
  3. Gaseous (steam)

Question 6.
Why are ice, liquid water and steam considered to have the same chemical substance ?
Answer:
Ice, liquid water and steam have same composition i.e. 2 parts hydrogen and one part oxygen by volume and same formula H2O, can be easily transformed from one state to other by heating or cooling.

Question 7.
How is a cloud formed ?
Answer:
Water from the surface of earth, lakes, seas, rivers, formed by plants (transpiration) etc. evaporates and rises high up in the atmosphere and condense into water droplets and collect to form cloud.

Question 8.
What is water cycle ? What is its importance ?
Answer:
Water cycle : The change of water from one form to another in nature which results in continuous circulation of water from earth’s surface to the atmosphere and from the atmosphere back to the earth’s surface is called water cycle.
Importance of water cycle:

  1. It assures a continuous supply of water to us.
  2. In controlling the climatic conditions all over the world.

Question 9.
How are the following formed ?

(a) fog
(b) mist
(c) dew
(d) frost

Answer:

(a) Fog : When water vapours change into tiny droplets of water near the ground, fog is formed.
(b) Mist: When tiny droplets of water remain suspended in air it is called mist.
(c) Dew : When the water vapour condenses on cold objects like grass, leaves and flowers in winter in the form of tiny droplets of water called dew.
(d) Frost: When the dew freezes it is called frost.

EXERCISE-II

Question 1.
Name:

(a) Two chemicals used to destroy germs present in water.
(b) Two diseases which spread through impure water.
(C) A chemical used for loading.
(d) Two substances which add taste to water.
(e) Two household methods to get safe drinking water.

Answer:
(a) Two chemicals used to kill germs in water are:

  1. Chlorine.
  2. Potassium permanganate.
  3. terilizing water with ozone.

(b) Two diseases are cholera, dysentry.
(c) Chemical used for loading is potash alum.
(d) Minerals and carbon dioxide gas adds taste to water.
(e) Methods to get safe drinking water:

  1. Adding chlorine tablets.
  2. By adding potassium permanganate crystals.

Question 2.
Answer in brief:

(a) Why is river water unfit for drinking?
(b) Why is tap water a mixture?
(c) What is mineral water?
(d) What is the purpose of adding bleaching powder to water supplied to the town?
(e) How is chemically pure water obtained in the laboratory?
(f) how is water in swimming pool kept free a germs?

Answer:

(a) River water contains mineral salts, suspended impurities like clay, sand particles, organic matter and bacteria and is not fit for drinking.
(b) Tap water contains, minerals, air, chlorine and other dissolved impurities that varies from place to place, therefore it is a mixture.
(c) Mineral water is pure water fit for drinking. It is collected from natural source and contains air, minerals and salts free from suspended impuiities, harmful bacteria and germs.
(d) Adding bleaching powder to water, kills germs and harmful bacteria and viruses present in water.
(e) Chemically pure water for laboratories is obtained-by distillation. Distilled water does not contain any salt or mineral
(f) Water in swimming pool kept free from infections and germs by chlorination i.e. treating water with chlorine gas.

Question 3.
Define:

(a) Sterilisation
(b) Sedimentation
(c) Loading
(d) Aeration

Answer:

(a) Sterilisation : The process of removal of microorganisms including bacterial spores from water to avoid water borne diseases is known as sterilisation.
(b) Sedimentation : The setting of suspended solid matter at the bottom of a liquid is called sedimentation.
(c) Loading : The process of adding a chemical to an impure liquid in order to increase the speed of sedimentation of suspended particles is called loading.
(d) Aeration : To kill harmful micro-organisms present in filtered water, air underpressure is blown into the filtered water. This process is called aeration.

Question 4.
What is potable water ? List four characteristics of potable water.
Answer:
Potable water : Water fit for drinking purposes is called potable water.
Four characters of drinking water :

  1. It should be transparent.
  2. Should have no colour, no odour.
  3. Should be free from harmful bacteria and germs.
  4. It should contain same salts and minerals needed by the body CO2 to add to taste.

Question 5.
Why is water important for plants and animals ?
Answer:
Importance of water for plants:

  1. Plants need water to prepare their food, for germination and growth to produce fruits, flowers etc.
  2. For conduction of food prepared by plants to other-parts of plant i.e., for translocation.
  3. Large number of plants live in water; water provides nutrients and oxygen for their survival.
    Crops need water for their growth. Water in the form of rain, washes the dust and smoke deposited on leaves by vehicles and helps the stomata in exchanging gases.

Importance of water for animals:

  1. Lot of water is lost by the body of animals by sweating, in the form of urine and evaporation while doing various activities, so to make up for the lost water animals consume a lot of water in the form of drinking.
  2. Water keeps the animals fresh and is natural medicine for their many ailments.
  3. Water is good solvent and helps in the process of digestion, blood circulation, excretion etc. in the body of organisms.
  4. Water is essential for the cleanliness of animals and their surroundings.

Question 6.
What are the three methods of removing germs from natural water. Explain.
Answer:
Three methods to remove germs :

  1. By boiling : Boiling kills germs present in water.
  2. Adding potassium permaganate: By adding potassium permaganate in the well the germs can be killed.
  3. Chlorination : After filtration water is passed through chlorination tank here chlorine kills the germs.

Question 7.
Name the steps involved in the purification of drinking water supplied in cities and towns.
Answer:
The water source for our towns and cities are river, lakes or underground water which contains suspended and dissolved impurities.
To remove these impurities steps involved are :

  1. Loading and sedimentation : to settle the suspended impurities to form a sediment for this purpose potash alum is added.
  2. Filtration : The water still contains lighter suspended impurities which are removed by filtration through sand and gravel. In cities ground water is drawn from tube well or submurcible pumps which have filters fitted in them. This clear water still contains germs.
  3. Chlorination : To kill germs water is passed into chlorination tank where it is treated with chlorine to kill germs.
    Water is now potable i.e. safer for drinking and supplied to homes.

Question 8.
What is the taste of distilled water ? Why is it not potable?
Answer:
Taste of water is tasteless i.e. flat. It is because distilled water does not contain any salt or mineral required for our body. So it is not potable water.

Question 9.
Give reasons :

(a) Ice floats on water.
(b) Marine life is able to survive in colder regions.
(c) Water droplets can be seen outside a chilled water bottle.

Answer:

(a) Water has maximum density at 4°C. Ice is lighter than water therefore it floats on water.
(b) This anomalous property of water enables aquatic plants and animals to survive in colder regions of world because even when the water of ponds, lakes, river freezes it freezes on the top but remains a liquid below ice layer.
(c) Sometimes we see water droplets on the outer surface of the glass containing ice-cold water, this is because the water vapour presents in’air, on coming in contact with the cold glass of water, loses energy and gets converted into liquid state, which we see as water droplets.

EXERCISE-III

Question 1.
Why is water called a universal solvent ?
Answer:
As water can dissolve in most of the substances, solids, liquid and gaseous. Therefore it is called universal solvent.

Question 2.
Define:

(a) Solute
(b) Solvent
(c) Solution
(d) Saturated solutions
(e) Unsaturated solutions

Answer:

(a) Solute : A solute is a substance that dissolves in a medium which can be water or any other substance. Solute is in smaller quantity in a solution.
(b) Solvent : A solvent is a medium in which a solute dissolves. It is in large quantity in a solution. Water is the most common solvent. The other solvents are alcohol, carbon tetrachloride etc.
(c) Solution : A solution is a homogeneous uniform mixture formed by a solute and a solvent.
(d) Saturated solution : When a solution cannot dissolve any more of solute at a given temperature, it is called saturated solution.
(e) Unsaturated solution : A solution that can take up more of the solute at a given temperature, is said to be an unsaturated solution.

Question 3.
State two factors by which solubility of a solute in a solvent can be increased.
Answer:
Two factors are :

  1. Stirring.
  2. Increase in temperature.

Question 4.
Why do aquatic animals die in boiled water ?
Answer:
Boiled water is deprived of oxygen i.e. there is no oxygen. For want of oxygen animals die in boiled water.

Question 5.
State three differences between water and air.
Answer:
Differences between water and air :
Water :

  1. Water is liquid and can exist in three states i.e. solid-ice, liquid-water, gas – vapours.
  2. Is a compound.
  3. H2O is its formula.

Air :

  1. Air is gaseous and can exist in liquid state when cooled under pressure.
  2. Is a mixture.
  3. Has no formula.

EXERCISE -IV

Question 1.
State four ways by which water can be conserved.
Answer:
Four ways to conserve water:

  1. Do not allow water to drip from defective taps.
  2. More dams should be built.
  3. More plantation should be done as plants help in bringing rain.
  4. Wastage of water should be avoided.
  5. Close the tap when you are brushing your teeth. Rather use a mug. Close the tap when you are washing clothes, open the tap only when you need it. Reduce, Reuse and recycle should be our mantra

Question 2.
Explain harvesting of water.
Answer:
When it rains heavily water runs into streets, drains and wasted we can not make use of it. Our purpose is to catch this rain water, store it for future use when we actually need it. For this harvesting of rain water should be done. Rain water is collected from the roofs and verandas of the buildings with the help of pipes and carried to tanks for storage and is used at the time of need when it is not raining.

Question 3.
What are the three main causes of water pollution ?
Answer:
Three main causes of water pollution :

  1. Addition of waste products from homes.
  2. Addition of waste products from agriculture.
  3. Addition of waste from industries.
  4. Addition of sewage in water bodies.

Question 4.
State the main steps to be taken to prevent water pollution.
Answer:
Steps to be taken to prevent water pollution :

  1. Trees and plants be planted along the banks of rivers and canals.
  2. Bathing and cleaning of animals near or in water sources be not allowed.
  3. Use of pesticides, insecticides, fungicides and fertilisers should be reduced.
  4. The polluted water from industries should be treated first and then discharged into water bodies.
  5. Use biodegradable detergents.
  6. Water containing sewage should be passed through sewage treatment plants first and then this water should be used for irrigation.
  7. Wells should be covered properly and washing and cleaning of clothes, utensils and animals should not be done near the well to keep them clean.

Question 5.
What are the causes of floods and drought?
Answer:
Problems cause by floods :

  1. A rise in the level of water in dams, rivers, lakes etc.
  2. Heavy rainfall also causes floods.
  3. Floods cause extensive damage to crops, property, animal and human life.
  4. Crop-fields, villages and”many low-lying areas get submerged under flood water.
  5. Rains/floods also affect smaller animals living in the soil.

Problems cause by drought :

  1. Crops may die, fodder may become scarce.
  2. Living organisms of the soil die.
  3. Animals may die, plants and trees will not survive.
  4. Soil becomes dry, water level in rivers, lakes, dams etc. may fall. The ground water-level falls.
  5. Drought displaces people from a large number of villages and towns.

Question 6.
State some of the ways in which you as an individual can conserve water.
Answer:
The ways in which we can conserve water are as follows :

  1. Use a bucket for taking it.
  2. Make sure, water does not overflow from overhead tanks of your house.
  3. Close the tap when you are brushing your teeth.
  4. Wash fruits, vegetable in a bowl of water, rather than under a running tap. Water used for washing vegetables may be used to water plants in the garden.

OBJECTIVE TYPE QUESTIONS

1. Fill in the blanks

(a) Water is a universal; solvent.
(b) Rainwater is the purest form of natural water.
(c) Sand and dust are suspended impurities in water.
(d) Sea water has high concentration of salt (impurity).
(e) Water covers nearly 4 / 5 th of the surface of the earth.
(f) Evaporation of rain water leaves NO residue.
(g) Potash alum is the chemical added to water to remove the tiny suspended particles.
(h) A solution is a uniform mixture of a solute and a solvent.
(i) Ice, water and steam have different physical states but are chemically identical.
(j) Boiling kills most of the germs in water.
(k) The elements present in the molecules of water are hydrogen and oxygen.

2. Write True or False for the following statements

(a) Water is an element.
Answer. False
Correct: Water is aL compound.

(b) Tap water does not contain dissolved impurities.
Answer. False
Correct: Tap water contain dissolved impurities.

(c) Alum is commonly used for removing suspended impurities.
Answer. False
Correct : Alum is commonly used for settling down of suspended impurities.

(d) Distillation is a good method for purifying water for town supply.
Answer. False
Correct : Distillation is a good method-for purifying water for medicinal purpose.

MULTIPLE CHOICE QUESTIONS

Tick (√) the correct alternative from the choice given for the following statements:

1. Water content in human body is

  1. 70%
  2. 75%
  3. 80%
  4. 90%

2. The purest form of natural water is

  1. seawater
  2. river water
  3. rainwater
  4. lake water

3. When the water vapour changes into tiny droplets of water near the ground, it is called

  1. mist
  2. dew
  3. fog
  4. frost

4. Water is a

  1. compound
  2. element
  3. mixture
  4. none of the above

5. Common salt is obtained from sea water by

  1. distillation
  2. crystallisation
  3. evaporation
  4. sublimation

6. Jaundice affects

  1. heart
  2. lungs
  3. liver
  4. kidney

7. Chlorination of water is done

  1. to kill the germs
  2. to remove the suspended impurities
  3. to remove the dissolved impurities
  4. none of the above

Selina Concise Biology Class 6 ICSE Solutions – Health and Hygiene

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Selina Concise Biology Class 6 ICSE Solutions – Health and Hygiene

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Biology. You can download the Selina Concise Biology ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Biology for Class 6 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 6 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Biology Chapter 6 Health and Hygiene

Review Questions 

Multiple Choice questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) Malaria is caused by:
(i) Bacteria
(ii) Protozoan
(iii) Fungi
(iv) Virus

(b) Deficiency of calcium causes
(i) Poor growth of teeth and gums
(ii) Goitre
(iii) Anaemia
(iv) Polio

(c) Hay fever and asthma are
(i) Deficiency diseases
(ii) Genetic diseases
(iii) Organic diseases
(iv) Allergy diseases

PQ. Cataract is a disease of:
(i) Ears
(ii) Nose
(iii) Eyes
(iv) Throat

(d) Infectious diseases can be prevented by:
(i) Medicines
(ii) Proper food
(iii) Immunisation
(iv) Exercise

(e) Which one of the following is a genetic disease?
(i) Scurvy
(ii) Leukemia
(lii) Goitre
(iv) Haemophilia

(f) Which one of the following is a degenerative disease?
(i) Thalassemia
(ii) Ben-ben
(iii) Cataract
(iv) Diabetes

(g) Pellagra is one disease caused by the deficiency of:
(i) Vit. B3
(ii) Vit. B1
(iii) Vit. C
(iv) Vit. D

(h) Deficiency of Iodine in one’s food can cause:
(i) Ben-ben
(ii) Goitre
(iii) Scurvy
(iv) Pellagra

(i) Which one of the following mineral deficiency diseases can be cured by eating a diet which include green leafy vegetables, banana, cereals, egg-yolk?
(i) Goitre
(ii) Anaemia
(iii) Brittle bones
(iv) Pain in muscle contraction

(j) Which one of the following vitamin deficiency diseases can be cured by eating a diet which includes carrot, yellow fruits, vegetables, butter, milk, fish ?
(i) Beri-beri
(ii) Dermatitis
(iii) Night blindness
(iv) Scurvy

(k) Which one of the following is a communicable disease?
(i) Measles
(ii) Cancer
(iii) Heart stroke
(iv) Allergy

Short Answer Questions:

Question 1(a).
What is a non-communicable disease ?
Answer:
The diseases which are caused due to improper functioning of the body organs e.g. diabetes, heart attack. They are not caused by germs and not transmitted from one to another.

Question 1(b).
What is a deficiency disease
Answer:
These disease are caused by lack of nutrients, vitamins, minerals as a anaemia, goitre.

Question 1(c).
What are communicable diseases ? How can they be avoided ?
Answer:
Those disease which spread from one person to another by the entry of microorganisms are known as communicable diseases. The disease-causing germs are called Pathogens. These disease can be avoided by proper vaccination, healthy food and hygenic surroundings.

Question 1(d).
Biting nails should be strictly avoided. Give reason.
Answer:
Nail biting may cause many disease as the dirt has many
bacteria causing diseases. Nails should be cut from time to time to save from diseases.

Question 1(e).
Regular exercise and proper rest is a must. Give reason.
Answer:
Regular exercise keeps our body strong and immune to many
diseases, rest refreshes our body.

Question 1(f).
 Children eating more of fast food tend to suffer from obesity (overweight). Comment.
Answer:
Fast food like pizza, burger, patty, oily foods etc. have much carbohydrates and fats. Children eating these become more and more fat and gain weight soon as they do not do much of physical work.

Question 1(g).
How can we control spreading of diseases by mosquitoes and houseflies ?
Answer:
We can control spreading of diseases by mosquitoes and houseflies by using repellants, throwing garbage in covered bins, avoiding stagnation of water and checking breeding of these insects.

2. Name the following:
(a) A bacterial disease caused due to contaminated water
Ans. A bacterial disease caused due to contaminated water Cholera.

(b) A disease caused due to Plasmodium
Ans. A disease caused due to Plasmodium Malaria.

(c) A disease caused due to the bite of female Culex mosquito
Ans. A disease caused due to the bite of female Culex mosquito Elephantiasis.

(d) A viral disease spread by the bite of a dog
Ans. A viral disease spread by the bite of a dog Rabies/ Hydrophobia

(e) Two diseases caused due to deficiency of protein in the diet of a child.
Ans. Kwashiorkor and marasmus.

(f) Any three water-borne disease.
Ans. Amoebiasis, Cholera, Hepatitis A.

(g) A viral disease caused due to unhealthy sexual contact
Ans. A viral disease caused due to unhealthy sexual contact AIDS.

(h) A disease caused due to choking of coronary artery
Ans. A disease caused due to choking of coronary artery Atheraosclerosis.

3. Write short (1-2 sentences) notes on the following:
Disease, immunisation, pathogen, allergy, AIDS.
Answer:
Disease: Disease is a departure from normal health due to structural or functional disorder of the body. Disease may be due to deficiency of nutrients or malfunctioning of organs or genetic disorders, improper metabolic activity, or allergies, or cancer and mental illness as diabetes, haemophilia, leukemia, schizophrenia.

Immunisation: It means, we make the body immune to certain diseases by introducing respective weakened germs into the body. Thus we develop resistance to the concerned disease this process is called immunisation. The germs or the material introduced into the body to make it resistant to the concerned disease is called vaccine. This produces antibodies in the body of the person and the person can be saved by these antibodies. The vaccine can be given by the injection or orally as polio drops, tap vaccine for typhoid, BCG vaccine for tuberculosis.

Pathogens: The germs that cause diseases to human beings and to other animals and plants are called pathogens. They spread the diseases from person to person or through the air or through the articles of the diseased persons. Pathogens may be different kinds of bacteria, viruses, fungi, protozoans or worms.

Allergy: Allergy is an unpredictable reaction to a particular substance. This type of substance is called allergen. Different people are allergic to different substances. A few common allergens are dust, spores, pollen, certain clothes, particular cosmetics, etc. The common areas of the body parts which are affected by allergies are skin, respiratory and digestive tracts. Asthma, eczema, diarrhoea, vomiting, nausea, etc. are some of the common allergic reactions.

AID’S (Acquired Immune Deficiency Syndrome): It is a viral disease caused by the virus called HTV (Human immuno deficiency virus) This virus makes the defence mechanism of the human body very weak. The immune system in the body as W.B.C. becomes weak. Thus the person catches the infectious diseases very easily. This disease spreads through sexual contact as one of the partner may be carrier of the disease. It may spread through the blood transfusion and infected syringes, blades of the barbers, it may infect the developing baby through the blood by the mother. It is very deadly disease.

4. Fill in the blanks by selecting suitable words given below: (clotting, goitre, insuline, rickets, iron, proteins)

  1. Anaemia is caused due to the deficiency of iron
  2. Deficiency of Vit. D causes rickets in children.
  3. Deficiency of iodine in the diet may cause goitre.
  4.  Kwashiorkor is caused due to the deficiency of proteins
  5. Diabetes is caused due to undersecretion of insulin.
  6. Haemophilia is a disease caused due to slow clotting of the blood.

5. Find the odd one out:

(a) Typhoid, cholera, aundice, tuberculosis, tetanus.
Ans. Jaundice is odd one

(b) Cold, malaria, measles, mumps.
Ans. Malaria is odd one.

(c) Scurvy, rickets, polio, pellagra, nightblindness.
Ans. Haemophilia is odd one.

(d) Proteins, carbohydrates, fats, minerals, cancer.
Ans. Cancer is odd one.

6. Fill in the blank in the following table:
Selina Concise Biology Class 6 ICSE Solutions - Health and Hygiene 1
Answer:
Selina Concise Biology Class 6 ICSE Solutions - Health and Hygiene 2

7. Given below is a crossword puzzle. Read the clues across and clues down, and fill up the blank squares. Check up your performance with the correct solution given at the end.
Clues across
1. Category of pathogen that causes diseases, like common cold and mumps.
5. This is the vaccine for preventing tuberculosis.
6. An organ usually affected by tuberculosis.
7. Jumbled spelling of one of the most common insect which visits our exposed foods and contaminates them.
8. Cover this part of your body by a handkerchief while sneezing to prevent droplet infection to others.
9. These may readily grow in your hair, if you do not wash it regularly.
10. A disease that weakens body’s defence system against infections.
Selina Concise Biology Class 6 ICSE Solutions - Health and Hygiene 3
Answer:
Clues down

  1. Germ or germ-substance introduced into the body to prevent occurrence of an infectious disease.
  2. A disease caused by an infected dog, and which affects the central nervous system.
  3. A disease in which the eyes, the skin and the urine turn yellow.
  4. The disease pertussis is popularly known as whooping

Selina Concise Biology Class 6 ICSE Solutions - Health and Hygiene 4

Long Answer Questions
Question 1.
Describe the ways in which communicable diseases are transmitted through various indirect methods.
Answer:
Indirect methods of transmission of communicable diseases:

  1. Using items used by the infected persons:
    The healthy persons may be infected by using the articles like towel, hankey, utensils, bedding used by the patient infected by the communicable diseases. Diseases like tuberculosis, ring worm, common cold, influenza are transmitted by this method.
  2. Contaminated food and water:
    Diseases like dysentery, cholera spread through the contaminated food and water. Flies sitting on the food, if taken by a healthy person may be infected by the germs which may cause vomiting and loose motions. Similarly water and food infected by entamoeba may cause dysentery to persons who may take contaminated food.
  3. Vectors or carriers: Organisms like mosquitoes and house flies, ticks carry germs from the source of infection and pass on the germs to the normal persons and thus they are infected by diseases like malaria, cholera, plague. These organisms which cany the disease are called vectors and are not infected themselves.Mosquitoes suck blood and carry the disease causing protozoans from infected persons to healthy persons. Similarly houseflies carry the germs from garbage and sewage to the food. If this food is taken by the persons they become prey to typhoid and other diseases.
  4. Air: One sneeze from a person infected by cold may give billions of germs which are carried by air and may infect the healthy person. Tuberculosis passes from one person to other by coughing or sneezing of the infected person.These germs remain suspended in the air and persons may be infected by these spores or germs. Common cold, measles, diptheria, chicken pox.

Question 2.
List 3 ways by which you should keep your environmentclean.
Answer:
We should keep our environment clean in following ways:
Cleanliness of Environment:

  1. Maintain a clean environment to prevent the spreading of diseases due to the breeding of mosquitoes, house flies and microorganisms.
  2. Garbage should be kept in covered bins so that flies do not breed on it.
  3. Do not allow water to stagnate outside your house and in your neighbourhood. All the drains should also be covered. This will prevent breeding of mosquitoes.

Question 3.
cine’s are prepared, giving the name of one disease for which each type of vaccine is used.
Answer:
For developing resistance in the body we introduce germs or germ substances in the body to develop resistance in the body against a particular disease. The material introduced into the body is called vaccine, this practice is called prophylaxis. The germ or the germ substance is put into the body orally as polio drops or it is introduced by injection as TAB vaccine. Vaccine or vaccination was attached with small pox, but it is now used in a general sense.
Preparation: 

  1. Killed germs are introduced into the body These act as vaccine for TAB, vaccine for typhoid, Salk’s vaccine for poliomyelitis. Rabies vaccine for dog bite.
  2. Living weakened germs: The living germs are treated in such a way that they become very weak and as such, they cannot cause the disease. They can induce antibody formation such as the vaccine for measles and the freezed dried BCG vaccine for tuberculosis.
  3. Living fully virulent germs: These virulent germs in small doses are introduced into the body as vaccine and these produce antibodies in the body and these do not allow the germs of particular type to cause that disease. In this vaccination the person is inoculated with cowpox virus. It is very similar to small pox virus.
  4. Toxoids: Toxoids are prepared from the extracts of toxins secreted by bacteria. These toxins are poisons and these are made harmless by adding formalin into them. They retain their capacity and as a result when introduced into the body they produce antibodies into the body and do not allow the germs to grow in the body as vaccines for diphtheria and tetanus.

Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid

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Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 8 Diseases and First Aid. You can download the Selina Concise Biology ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Biology for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Biology ICSE SolutionsChemistryPhysicsMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Biology Chapter 9 Diseases and First Aid

REVIEW QUESTIONS

Multiple Choice questions:

1. Put a tick mark (✓) against the correct alternative in the following statements:

(a) A mosquito is a vector for

  1. Typhoid
  2. Cholera
  3. Malaria
  4. Jaundice

(b) Dengue is caused by a

  1. Protozoan
  2. Virus
  3. Worm
  4. Fungus

(c) The idea of vaccination was conceived by

  1. Charles Darwin
  2. Alexander Flemming
  3. Issac Newton
  4. Edward Jenner

(d) Which one of the following is not a psychotropic drug ?

  1. Morphine
  2. Cocaine
  3. Heroin
  4. Penicillin

(e) Which one of the following is a communicable disease ?

  1. Measles
  2. Cancer
  3. Heart stroke
  4. Allergy

(f) Cataract is a disease of: –

  1. Ears
  2. Nose
  3. Eyes
  4. Throat

(g) Infectious diseases can be prevented by:

  1. Medicines
  2. Proper food
  3. Immunisation
  4. Exercise

(h) Which one of the following is a genetic disease ?

  1. Scurvy
  2. Leukemia
  3. Goitre
  4. Haemophilia

(i) Which one of the following is a degenerative disease ?

  1. Thalassemia
  2. Beri-beri
  3. Cataract
  4. Diabetes

(j) Pellagra is one disease caused by the deficiency of:

  1. Vit. B3
  2. Vit. B1
  3. Vit. C
  4. Vit. D

(k) Hay fever and asthma are

  1. Deficiency diseases
  2. Genetic diseases
  3. Organic diseases
  4. Allergy diseases

(I) Which one of the following vitamin deficiency diseases can be cured by eating a diet which includes carrot, yellow fruits, vegetables, butter, milk, fish ?

  1. Beri-beri
  2. Dermatitis
  3. Night blindness
  4. Scurvy

Short Answer Questions:

Question 1(a).
What is a non-communicable disease ?
Answer:
The diseases which are caused due to improper functioning of the body organs e.g. diabetes, heart attack. They are not caused by germs and not transmitted from one to another.

Question 1(b).
What are communicable diseases ?
Answer:
Those disease which spread from one person to another by the entry of microorganisms are known as communicable diseases.

Question 1(c).
How can we control spreading of diseases by mosquitoes and houseflies ?
Answer:
We can control spreading of diseases by mosquitoes and houseflies by using repellants, throwing garbage in covered bins, avoiding stagnation of water and checking breeding of these insects.

Question 1(d).
Public hygiene is equally important as personal hygiene. Give reasons.
Answer:
Keeping oneself clean is personal hygiene. But public hygiene is equally important as dirty surrounding may lead to more of houseflies, mosquitoes and other insects which are major vectors of many communicable diseases. Clean surrounding also provides good mental health as it soothes our mind.

Question 1(e).
What is a deficiency disease ?
Answer:
These disease are caused by lack of nutrients, vitamins, minerals as a anaemia, goitre.

Question 1(f).
Biting nails should be strictly avoided. Give reason.
Answer:
Nail biting may cause many disease as the dirt has many bacteria causing diseases. Nails should be cut from time to time to save from diseases.

Question 1(g).
Regular exercise and proper rest is a must. Give reason.
Answer:
Regular exercise keeps our body strong and immune to many diseases, rest refreshes our body.

Question 1(h).
Children eating more of fast food tend to suffer from obesity (overweight). Comment.
Answer:
Fast food like pizza, burger, patty, oily foods etc. have much carbohydrates and fats. Children eating these become more and more fat and gain weight soon as they do not do much of physical work.

2. Name the following:

Question 2(a).
A viral disease caused due to unhealthy sexual contact
Answer:
AIDS.

Question 2(b).
A disease caused due to Plasmodium
Answer:
Malaria.

Question 2(c).
A disease caused by the bite of female Anopheles mosquito
Answer:
Malaria.

Question 2(d).
Two viral diseases caused by mosquito bites
Answer:
Dengu, Chikungunya.

Question 2(e).
Any droplet — borne disease.
Answer:
Amoebiasis, Cholera, Hepatitis A.

Question 2(f).
A viral disease caused by the bite of a dog
Answer:
Rabies/Hydrophobia

Question 2(g).
A disease due to choking of coronary artery
Answer:
Atheraosclerosis.

Question 2(h).
Two diseases caused due to deficiency of protein in the diet of a child.
Answer:
Kwashiorkor and marasmus.

3. Write short (2-3 sentences) notes on the following:
Disease, immunisation, pathogen, AIDS, vaccination, vector.

Answer:

Disease: Disease is a departure from normal health due to structural or functional disorder of the body. Disease may be due to deficiency of nutrients or malfunctioning of organs or 1 genetic disorders, improper metabolic activity, or allergies, or cancer and mental illness as diabetes, haemophilia, leukemia, schizophrenia.

Immunisation: It means, we make the body immune to certain diseases by introducing respective weakened germs into the body. Thus we develop resistance to the concerned disease this process is called immunisation. The germs or the material introduced into the body to make it resistant to the concerned disease is called vaccine. This produces antibodies in the body of the person and the person can be saved by these antibodies. The vaccine can be given by the injection or orally as polio drops, tap vaccine for typhoid, BCG vaccine for tuberculosis.

Pathogens: The germs that cause diseases to human beings and to other animals and plants are called pathogens. They spread the diseases from person to person or through the air or through the articles of the diseased persons. Pathogens may be different kinds of bacteria, viruses, fungi, protozoans or worms.

AID’S (Acquired Immune Deficiency Syndrome): It is a viral disease caused by the virus called HIV (Human immuno deficiency virus) This virus makes the defence mechanism of the human body very weak. The immune system in the body as W.B.C. becomes weak. Thus the person catches the infectious diseases very easily. This disease spreads through sexual contact as one of the partner may be carrier of the disease. It may spread through the blood transfusion and infected syringes, blades of the barbers, it may infect the developing baby through the blood by the mother. It is very deadly disease.

Vaccination: Vaccination is a method of making the body immune to a particular disease by injecting killed or weakened disease causing microbe into a body to stimulate the formation of antibodies and develop immunity to that disease causing microbe.

Vector: A vector is an organism that carries disease causing microbes (pathogens) from one host to another. They are the carriers of infection. Example: Mosquito, housefly, etc.

P.Q. Fill in the blanks by selecting suitable words given below:
(clotting, goitre, insuline, rickets, iron, proteins)

(a) Anaemia is caused due to the deficiency of iron.
(b) Deficiency of Vit. D causes rickets in children.
(c) Deficiency of iodine in the diet may cause goitre.
(d) Diabetes is caused due to undersecretion of insulin.
(e) Kwashiorkor is caused due to the deficiency of proteins.
(f) Haemophilia is a disease caused due to slow clotting of the blood.

P.Q. Find the odd one out:

(a) Typhoid, cholera, jaundice, tuberculosis, tetanus.
Jaundice is odd one
(b) Cold, AIDS, plague, malaria, measles.
Malaria is odd one.
(c) Scurvy, rickets, haemophilia, pellagra, night blindness.
Haemophilia is odd one.
(d) Proteins, carbohydrates, fats, minerals, cancer.
Cancer is odd one.

P.Q. Fill in the blank in the following table:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 1
Answer:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 2
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 3

Long Answer Questions:

Question 1.
What is vaccination? Mention the four ways in which vaccine’s are prepared, giving the name of one disease for which each type of vaccine is used.
Answer:
For developing resistance in the body we introduce germs or germ substances in the body to develop resistance in the body against a particular disease. The material introduced into the body is called vaccine, this practice is called prophylaxis.
The germ or the germ substance is put into the body orally as polio drops or it is introduced by injection as TAB vaccine. Vaccine or vaccination was attached with small pox, but it is now used in a general sense.

Preparation:

  1. Killed germs are introduced into the body These act as vaccine for TAB, vaccine for typhoid, Salk’s vaccine for poliomyelitis. Rabies vaccine for dog bite.
  2. Living weakened germs: The living germs are treated in such a way that they become very weak and as such, they cannot cause the disease. They can induce antibody formation such as the vaccine for measles and the freezed dried BCG vaccine for tuberculosis.
  3. Living fully virulent germs: These virulent germs in small doses are introduced into the body as vaccine and these produce antibodies in the body and these do not allow the germs of particular type to cause that disease: In this vaccination the person is inoculated with cowpox virus. It is very similar to small pox virus.
  4. Toxoids: Toxoids are prepared from the extracts., of toxins secreted by bacteria. These toxins are poisons and these are made harmless by adding formalin into them. They retain their capacity and as a result when introduced into the body they produce antibodies into the body and do not allow the germs to grow in the body as vaccines for diphtheria and tetanus.

Question 2.
Burns can be superficial burns, deep burns or chemical burns. What emergency care you would suggest in each case.
Answer:
When one gets burnt up accidentaly one should not pull clothes from the burnt area and one should not cut the blisters. One should apply butter, vaseline or ointment.

  • Superficial burns: When there are superficial bums, put cold water on it and apply some oily substance, bumol, castor oil, vaseline, butter etc.
  • Deep burns: When there are deep bums do not put cold water on the burnt area. Seek the help of hospital and one should be kept under the treatment of some expert doctor of skin.
  • Chemical burns: In case of chemical burns i.e., due to acid and other chemicals, wash with running water for 10 minutes and then cover with dressing.

Question 3.
Describe the ways in which communicable diseases are transmitted through various indirect methods.
Answer:
Indirect methods of transmission of communicable diseases:

  1. Using items used by the infected persons: The healthy persons may be infected by using the articles like towel, hankey, utensils, bedding used by the patient infected by the communicable diseases. Diseases like tuberculosis, ring worm; common cold, influenza are transmitted by this method.
  2. Contaminated food and water: Diseases like dysentery, cholera spread through the contaminated food and water. Flies sitting on the food, if taken by a healthy person may be infected by the germs which may cause vomiting and loose motions. Similarly water and food infected by entamoeba may cause dysentery to persons who may take contaminated food.
  3. Vectors or carriers: Organisms like mosquitoes and house flies, ticks carry germs from the source of infection and pass on the germs to the normal persons and thus they are infected by diseases like malaria, cholera, plague. These organisms which carry the disease are called vectors and are not infected themselves.
    Mosquitoes suck blood and carry the disease causing protozoans from infected persons to healthy persons.
    Similarly houseflies carry the germs from garbage and sewage to the food. If this food is taken by the persons they become prey to typhoid and other diseases.
  4. Air: One sneeze from a person infected by cold may give billions of germs which are carried by air and may infect the healthy person. Tuberculosis passes from one person to other by coughing or sneezing of the infected person.
    These germs remain suspended in the air and persons may be infected by these spores or germs. Common cold, measles, diptheria, chicken pox.

Question 4.
Given a crossword puzzle. Read the clues across and clues downward, and fill up the blank squares. Check up your performance with the correct solution given at the end.

Clues across

  1. Category of pathogen that causes diseases, like common cold and mumps.
  2. These may readily grow in your hair, if you do not wash it regularly.
  3. This is the vaccine for preventing tuberculosis.
  4. Cover this part of your body by a handkerchief while sneezing to prevent droplet infection to others.
  5. The disease pertussis is popularly known as whooping
  6. One of the most common insects which visits our exposed foods and contaminates them.
  7. A disease that weakens body’s defence system
    Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 4
  8. Germ or germ – substance introduced into the body to prevent occurrence of an infectious disease.
  9. A disease in which the eyes, the skin and the urine turn yellow.
  10. An organ usually affected by tuberculosis.
  11. A disease caused by the bite of an infected dog, and which affects the central nervous system.

Answer:
Selina Concise Biology Class 8 ICSE Solutions – Diseases and First Aid 5

Selina Concise Chemistry Class 8 ICSE Solutions – Hydrogen

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Selina Concise Chemistry Class 8 ICSE Solutions – Hydrogen

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 7 Hydrogen. You can download the Selina Concise Chemistry ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Chemistry for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Class 8 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 7 Hydrogen

Points to Remember:

  1. Hydrogen is the most abundant element found in the universe.
  2. Hydrogen is much more common in the form of compounds. The most important compound of hydrogen is water.
  3. The chief sources of hydrogen are water, acids and alkalies.
  4. Hydrogen is prepared by the action of water, acids or alkalies on active metals.
  5. Electrolysis of water results in the formation of hydrogen and oxygen.
  6. Hydrogen is lighter than air.
  7. Hydrogen bums in air with pop sound.
  8. Hydrogen acts as a reducing agent.
  9. Hydrogen is used to produce oxyhydrogen flame and in weather forecast balloons.

Exercise

1. Fill in the blanks:

(a) Hydrogen is lighter than air.
(b) Hydrogen is sparingly soluble in water.
(c) Hydrogen bums with a oxyhydrogen pale blue flame and pop sound is heard.
(d) A metal sodium hydrogen in the reactivity series gives hydrogen with water.
(e) Hydrogen reacts with metal oxides to form metal and water.
(f) Oxidation is the removal of hydrogen and addition of oxygen.
(g) In redox reaction oxidation and reduction occur simultaneously.

2. Indicate which of the following statements are true and which are false:

(a) Hydrogen molecule is monovalent.
(b) The removal of hydrogen from a substance is called reduction.
(c) Nitric acid can not be used to prepare hydrogen by its action on active metals ?
(d) The reaction between hydrogen and nitrogen to form ammonia is reversible.
(e) Zinc can liberate hydrogen from water, acid and alkali solution.
(f) Hydrogen is combustible as well as a supporter of combustion.
(g) Hydrogen gas is easily liquefiable.
Answer:
(a) False
(b) True
(c) False. Hydrogen cannot be prepared by the action of nitric acid on metals because it also releases nitrous oxide and nitric oxide.
(d) True
(e) True
(f) False
(g) False

3. Complete and balance the following equations:

selina-concise-chemistry-class-8-icse-solutions-hydrogen-1
selina-concise-chemistry-class-8-icse-solutions-hydrogen-2

4. Give reasons for the following:

(a) Hydrogen be used as a fuel?
(b) Though hydrogen is lighter than air it cannot be collected by downward displacement of air.
(c) A pop sound produced when hydrogen is burnt?
(d) Helium replaced hydrogen in weather observation balloons?
(e) Nitric acid not used for the preparation of hydrogen gas?
(a) Because of its high heat of combustion, it is used as a fuel.
Answer:
(a) Coal gas, water gas and liquid hydrogen are some significant fuel.
(b) Since hydrogen is lighter than air. it is possible to collect the gas by downward displacement of air. But it is not safe to do so since a mixture of hydrogen and air can lead to an explosion.
(c) Impure hydrogen gas bums in air with a pop sound. This is because of the presence of impurities in it.
(d) If there is small leakage of hydrogen in a balloon, it forms a mixture with air that can explode. So helium has replaced hydrogen.
(e) Hydrogen cannot be prepared by the action of nitric acid on metals because it also releases nitrous oxide and nitric oxide and oxides the hydrogen to form water.

5. Name the following:
(a) Two metals which give hydrogen with cold water.
(b) A metal which liberates hydrogen only when steam is passed over red hot metal.
(c) The process in which oxygen is added or hydrogen is removed.
(d) A metallic oxide which can be reduced into metal by hydrogen.
Answer:
(a) Sodium (Na) and Potassium (K) give hydrogen with cold water.
(b) Iron
(c) Oxidation
(d) Copper oxide (CuO)

6. (a) Name the chemicals required to prepare hydrogen
gas in the laboratory.
(b) Give a balanced chemical equation for the reaction.
(c) Draw a neat and well-labelled diagram for the laboratory preparation ofhydrogen.
(d) How is hydrogen gas collected?
Answer:
(a) Granulated Zinc and dil. Hydrochloric acid.
(b) Zn + 2 HCl → ZnCl2 + H2 (g)
(c)
selina-concise-chemistry-class-8-icse-solutions-hydrogen-3
(d) Hydrogen gas is collected by the down-ward displacement of water.

7. How would you show that hydrogen:
(a) is a non-supporter of combustion?
(b) is lighter than air?
Answer:
(a) Hold a hydrogen gas filled jar with its mouth downwards.
Place a lighted candle inside the jar. The candle gets extinguished but the gas bums with a pop sound. This shows that hydrogen is non-supporter of combustion.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-4

(b) Take a delivery tube and place one of its ends in a soap solution kept in a trough and the other one in a flat bottom jar as shown in the figure. The soap bubbles containing hydrogen rise upward the air. The rising soap bubbles prove that hydrogen is lighter than air.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-5
Hydrogen-filled soap bubbles rising upward in the soap solution and into the air shows that hydrogen is lighter than air.

8. Hydrogen is a good reducing agent: What do you understand by the above statement? Explain with the help of copper oxide as an example.
Answer:
Hydrogen acts as a good reducing agent means, when hydrogen gas is passed over hot metallic oxides of copper, lead, iron, etc. it removes oxygen from them and thus reduces them to their corresponding metal.
Let us consider the following example, in each of which metallic oxide react with hydrogen. Metallic oxide act as oxidising agents and hydrogen acts as a reducing agents.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-6

9. (a) Name a process by which hydrogen gas is manufactured.
(b) Give equations for the reactions.
(c) How is hydrogen separated from carbon dioxide and carbon monoxide?
Answer:
(a) Commercially, hydrogen is prepared by Bosch process.

(b) (i) Steam is passed over hot coke at 1000°C in a furnace called converters. As a result water gas is produced which is a mixture of carbon monoxide and hydrogen gases.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-7
This reaction is endothermic in nature.
(ii) Water gas is mixed with excess of steam and passed over a catalyst ferric oxide (Fe2O3) and a promotor chromium trioxide (Cr2O3).
selina-concise-chemistry-class-8-icse-solutions-hydrogen-8
This reaction is exothermic in nature

(c) (i) The products are hydrogen, carbon dioxide and some
unreacted carbon monoxide. Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, in which carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash (KOH) solution.
2KOH + CO2 → K2CO3 + H2O
(ii) To separate carbon monoxide the gaseous mixture is passed through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-9
Thus hydrogen gas is obtained.

10. Match the statements in Column A with those in Column B.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-10

11. State four uses of hydrogen:
Answer:

  1. Hydrogen with oxygen produce oxy-hydrogen flame which is used for cutting and welding.
  2. Hydrogen gas is used as a fuel.
  3. Hydrogen is used for hydrogenation of vegetable oil.
  4. Hydrogen gas is used extensively in the manufacture of ammonia gas, which is used to produce fertilizers.

12. Define:
(a) catalytic hydrogenation (b) oxidation
(c) reduction (d) redox reaction
Answer:
(a) Catalytic hydrogenation: catalytic hydrogenation is a process by which hydrogen gas is passed through vegetable oils in the presence of catalyst like Ni, Pt or Pd to convert them into solid vanaspati ghee.

(b) Oxidation: A reaction in which a substance combine with oxygen or in which hydrogen is removed is called oxidation reaction.
Example: H2S + Cl → 2HCl + S

(c) Reduction: Those reactions in which hydrogen combines with a substance or oxygen is removed from a substance, are known as reduction reactions.
selina-concise-chemistry-class-8-icse-solutions-hydrogen-11

(d) Redox reaction: Redox reactions are those in which reduction and oxidation both takes place simultaneously i.e. one substance is reduced while the other gets oxidised.

13. Multiple Choice Questions

(a) Equal volumes of hydrogen and chlorine are exposed to diffused sunlight to prepare

  1. hydrogen chloride
  2. water
  3. sodium hydroxide
  4. hydrochloric acid

(b) The metal which reacts with cold water to produce hydrogen is

  1. magnesium
  2. aluminium
  3. calcium
  4. iron

(c) In metal activity series the more reactive metals are at

  1. top
  2. bottom
  3. middle
  4. none

(d) Hydrogen is responsible for producing

  1. heat and light
  2. hydrogenated oil
  3. fertilizers
  4. all of the above

(e) Hydrogen is

  1. combustible
  2. non-combustible
  3. supporter of combustion
  4. neither supporter nor combustible

(f) Water gas is a mixture of

  1. carbon monoxide and oxygen
  2. carbon monoxide and hydrogen
  3. hydrogen and oxygen
  4. hydrogen and nitrogen.

Selina Concise Physics Class 8 ICSE Solutions – Physical Quantities and Measurement

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Selina Concise Physics Class 8 ICSE Solutions – Physical Quantities and Measurement

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Physics Chapter 2 Physical Quantities and Measurement. You can download the Selina Concise Physics ICSE Solutions for Class 8 with Free PDF download option. Selina Publishers Concise Physics for Class 8 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

Selina Concise physics Class 8 ICSE SolutionsChemistryBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions For class 8 Physics chapter 2 – Physical Quantities and Measurement

  • MASS Is the quantity of matter contained in a body.
    VOLUME is the space occupied by body.
  • Equal mass of IRON and cotton, iron will have less volume than cotton.
  • Equal volume of Iron and cotton, the mass of iron is more than mass of cotton, because iron denser than cotton.
  • DENSITY “Is ratio of mass of substance to volume of substance”
    D = M/V = KG/M3 The SI. unit of density is kg M-3
  • Density of a substance does not change with change in shape or size.
  • When a substance is heated it expands and volume increases. Hence density decreases.
    Water has maximum density at 4°C i.e. density of water increases from 0°C to 4°C and decreases above 4°C.
  • Volume of substance is measured by formula V = L × B × H or 4/3 or by measuring cylinder.
  • Mass is measured by beam balance or spring balance.
  • RELATIVE DENSITY of substance is the density compare with water i.e. How many times the substance is DENSER than water. Since density of water is 1  Gcm-3, so density of a substance in Gcm-3 = relative density of substance.
    S.I. unit of R.D. > has no units — since it is the ratio of same
    quantities.
  • If a substance has density more than liquid it SINKS in the liquid and if the density of substance is LESS than liquid it floats on liquid.
  • BUOYANT FORCE “The force exerted by liquid acting vertically
    upward on a body and is equal to the weight of liquid displaced by its immersed part.”
  • Weight of body Acting vertically downward. This force has the tendency to sink the body.
  •  LAW OF FLOATATION “When a body floats in a liquid, the weight of the liquid displaced by its immersed part is equal to the total weight of the body.” While floating
    wt. of floating body W=wt. of liquid displaced by its immersed part FB i.e. Apparent wt. of floating body is zero.
    Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 1

Density of body is greater than density of liquid. The body sinks.

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 2

Density of body is equal to the density of liquid. The body float where ever it is left in liquid.

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 3

Density of body is less than density of liquid. The body rises to the surface and floats.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) Equal volumes of the two different substances have equal masses.
Answer False.
Equal volumes of the two different substances have different masses.

(b) The density of a piece of brass will change by changing its size or shape.
Answer False.

(c) The density of a liquid decreases with increase in its temperature.
Answer True.

(d) Relative density of water is 1.0.
Answer True.

(e) Relative density of a substance is expressed in g cm-3.
Answer False.
Relative density of a substance has no units.

(f) When a body is immersed in a liquid, the buoyant force experienced by the body is equal to the volume of the liquid displaced by it.
Answer False.
The buoyant force is equal to the weight of the liquid displaced by the immersed part of body.

(g) A body experiences the same buoyant force while floating in watr or alcohol.
Answer True.

(h) A body experiences the same buoyant force when it floats or sinks in water.
Answer False.

(i) A body floats in a liquid when its weight becomes equal to the weight of the liquid displaced by its submerged part. .
Answer True.

(j) A body while floating, sinks deeper in a liquid of low density than in a liquid of high density.
Answer True.

2. Fill in the blanks

(a) 1 kg is the mass of 1000 ml of water at 4°C.
(b) Mass = density x volume.
(c) The S.I. unit of density is Kg m-3
(d) Density of water is 1000 Kg m-3.
(e) 1 g cm-3 = 1000 Kg m-3.
(f) The density of a body which sinks in water is more than 1000 Kg m-3.
(g) Abody sinks in a liquid A, butt floats in a liquid B. The density of liquid A is less than the density of liquid B.
(h) A body X sinks in water, but a body Y floats on water. The density of the body X is more than the density of body Y.
(i) The buoyant force experienced by a body when floating in salt¬water is equal to or same that of when floating in pure water.
(j) The weight of a body floating in a liquid is zero.

3. Match the following

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 4

4. Select the correct alternative 

(a) The correct relation is

  1. Density = Mass x Volume
  2. Mass = Density x Volume
  3.  Volume = Density x Mass
  4. Density = Mass + Volume

(b) The relative density of alcohol is 0.8. Its density is

  1.  0.8
  2. 800 kg nr3
  3.  800 g cm-3
  4. 0.8 kg m-3

(c) A block of wood of density 0.8 g cm-3 has a volume of 60 cm3. The mass of block is

  1.  60.8 g
  2.  75 g
  3. 48 g
  4. 0.013 g

(d) The density of aluminium is 2.7 g cm-3 and that of brass 8.4 g cm’3. The correct statement is

  1.  Equal masses of aluminium and brass have equal volumes
  2. The mass of a certain volume of brass is more than the mass of equal volume of aluminium.
  3.  The volume of a certain mass of brass is more than the volume of equal mass of aluminium.
  4.  Equal volumes of aluminium and brass have equal masses.

(e) A density bottle has a marking 25 mL on it. It means that:

  1.  the mass of density bottle is 25 g
  2. the density bottle will store 25 ml of any liquid in it
  3.  the density bottle will store 25 ml of water, but more volume of liquid denser than water.
  4.  the density bottle will store 25 ml of water, but more volume of a liquid lighter than water.

(f) The correct statement is

  1.  The buoyant force on a body is equal to the volume of the liquid displaced by it ‘
  2. The buoyant force on a body is equal to the volume of the body
  3. The buoyant force on a body is equal to the weight of the liquid displaced by it
  4.  The buoyant force on a body is always equal to the weight of the body.

(g) A piece of wood floats on water. The buoyant force on wood will be

  1.  zero
  2.  more than the weight of the wood piece
  3. equal to the weight of the wood piece
  4. less than the weight of the wood piece.

(h) The weight of a body is more than the buoyant force experienced by it, due to a liquid. The body will

  1. sink
  2.  float with its some part outside the liquid
  3.  float just below the surface of liquid
  4. float with whole of its volume above the surface of liquid.

B. Short/Long Ans Questions 

Question 1.
Define the term density of a substance.
Answer:
Density of a substance is defined as “Mass per Unit volume”.

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 5

Question 2.
Name the S.I. unit of density. How is it related to g Cm-3 ?
Answer:
S.I. unit of density is kg M-3 In C.GS. system unit of mass is g and unit of volume is Cm3, so CGS unit of density is g Cm-3 (gram per cubic centimetre)
Relationship between S.I. and C.GS. units

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 6

Question 3.
The density of brass is 8.4 g cm-3. What do you mean by this statement ?
Answer:
This statement meAns one cubic centimetre volume of brass has mass of 8.4 g.

Question 4.
Arrange the following substances in order of their increasing density:
Iron, Cork, Brass, Water, Mercury.
Answer:
Cork, Water, Iron, Brass, Mercury.

Question 5.
How does the density of a liquid (or gas) vary with temperature?
Answer:
Most of the liquids increase in volume with increase in temperature, but water shows anomalous behaviour. Water has maximum volume at 4°C and maximum density at 4°C.
Actually, when volume increases density decreases and when volume decreases the density increases.
But water when cooled from a high temperature, contracts upto 4°C because volume decreases and expands when cooled further below 4°C and hence density of water increases when it is cooled upto 4°C while decreases when cooled further below 4°C. In other words, the density of water is maximum at 4°C equal to 1 g Cm-3 or lOOO kg m-3.

Question 6.
A given quantity of a liquid is heated. Which of the following quantity will vary and how ?
(a) mass, (b) volume and (c) density
Answer:
When a given quantity of liquid is heated
(a) Mass : does not change.
(b) Volume: changes and increases with rise in temperature.
(c) Density : Changes and decreases.
Density = Mass / volume

Question 7.
Describe an experiment to determine the density of the material of a coin.
Answer:
Density = Mass / volume
To find the density of the material of a coin, we need to find its (i) mass—by common beam balance and (ii) Its volume by measuring cylinder.
Measure the mass of coin.
EXPERIMENT – Let the mass of coin shown by beam balance = M (gram) = 50 g (ray)
Measure the vol. of coin.
Initial volume of water = V1 = 40 ml (say)
Final volume of water
When coin is added in the cylinder=V2 = 50 ml (say)
Then vol. of coin = V2 – V1 = 50 – 40 = 10 ml

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 7

Question 8.
Describe an experiment to determine the density of a liquid.
Answer:
To determine the density of a liquid D = M / V
We need to find (i) the vol. of liquid say milk, (ii) mass of liquid.
EXPERIMENT:
(i) To find the mass of milk:
wt. of empty 100 c.c beaker = M1 g = 70 g (say)
Fill the beaker (half) with milk and weigh again=M2 g = 116 g (say)
(ii) To find the vol. of milk:
TrAnsfer this milk into measuring cylinder and note the volume V = 40 c.c (say)

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 8
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 9

Question 9.
What is a density bottle ? How is it used to find the density of a liquid ?
Answer:
DENSITY bottle is a small glass bottle having a glass stopper at its neck. The bottle can store a fixed volume of a liquid. Generally the volume of bottle is 25 ml or 50 ml. Stopper has a narrow hole through it. When bottle is filled with liquid and stopper is inserted, THE EXCESS LIQUID RISES THROUGH THE HOLE and drains out. Thus the bottle will contain the same volume of liquid each time when it is filled. It is used to determine the density of a liquid.

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 10

 

Question 10.
Define the term relative density of a substance.
Answer:
RELATIVE DENSITY: “is the ratio of density of a substance to the density of water at 4° C.”
Or
RELATIVE DENSITY “is theratio of mass of the substance to the mass of an equal volume of water at 4° C.”

Question 11.
What is the unit of relative density ?
Answer:
UNIT OF RELATIVE DENSITY: No units since it is a pure ratio.

Question 12.
Distinguish between density and relative density.
Answer:
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 11

Question 13.
Explain the meaning of the statement ‘relative density of aluminium is 2.7’ ?
Answer:
The statement ‘Relative density of aluminium is 2.7’ meAns .
A piece of aluminium of any volume has mass 2.7 times that of an equal volume of water.
i.e. Aluminium is 2.7 times heavier than water.

Question 14.
How does the density of a body and that of a liquid determine whether the body will float or sink into that liquid ?
Answer:
If the density of a body is LESS than the density of LIQUID, the body will FLOAT on the surface of liquid.
If the density of a body is MORE than the density of liquid, the body will SINK in a liquid.

Question 15.
A cork piece floats on water surface while an iron nail sinks in it. Explain the reason.
Answer:
CORK floats on water meAns density of cork is LESS than density of water.
IRON nail: Sinks in water meAns density of iron nail is MORE than density of water.

Question 16.
Which of the following will sink or float on water ? (Densityof water = 1 g Cm-3)
(a) body A having density 500 kg m-3
(b) body B having density 2520 kg m-3
(c) body C having density 1100 kg m-3
(d) body D having density 0.85 g m-3
Answer:
Density of water = 1 g Cm-3
(a) Density of body A = 500 kg m-3 = 500 × = 0.5 = 0.5 g Cm-3
Density of body A ¡s less than density of water hence A will float on water
(b) Density of body B = 2520 kg m-3 = 2520 × 1/1000 = 2.52 g Cm-3
Density of body B is more than density of water and hence B will SiNK in water
(c) Density of body C = 1100kg m-3 = 1100 × 1/1000 = 1.1 g Cm-3
is greater than water.
Hence, body C will sink in water.
(d) Density of body D = 0.85 g Cm-3 < 1.0 g Cm-3
Density of body D is less than the density of water hence body D will FLOAT on water

Question 17.
What is the iaw of floatation ?
Answer:
When a body floats in a liquid, the weight of the liquid displaced by its immersed part is equal to the total weight of the body. This is the law of floatation, i.e. while floating. Weight of the floating body = Weight of the liquid displaced by its immersed part.

Question 18.
The density of water is 1.0 g Cm-3. The density of iron is 7.8 × 10″3 g Cm-3. The density of mercury is 13.6 g Cm-3.
Ans the following:
(a) Will a piece of iron float or sink in water ?
(b) Will a piece of iron float or sink in mercury ?
Answer:
Density of water 1.0 g Cm-3
(a) Density of piece of iron = 7.8 × 10-3 g Cm-3
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 12
∴ Density of piece of iron is LESS than density of water.
Hence, piece of iron will FLOAT in water.
(b) Density of piece of iron = 7.8 × 10-3
Density of mercury is 13.6 × 10-3 g Cm-3
Since 7.8 × 10-3 < 13.6 × 10-3
∴ Density of piece of iron is LESS than density of mercury
∴ Piece of iron will FLOAT in mercury

Question 19.
The diagram given below show a body floating in three different liquids. A, B and C at different levels.
(a) In which liquid does the body experience the greatest buoyant force ?
(b) Which liquid has the least density ?
(c) Which liquid has the highest density ?

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 13Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 14
Answer:
(a) Buoyant force is same in each case as the wt. of body is same in each case and Buoyant force is equal to the weight of liquid displaced by the immersed part of body which balances the wt. of body.
(b) The liquid A has the least density as body immerses the maximum.
(c) Liquid C has the highest density as the body immerses the least.

Question 20.
For a floating body, how is its weight related to the buoyant force ?
Answer:
When a body floats in a liquid. The weight of the liquid displaced by its immersed part is equal to the total weight of the body.

Question 21.
Why does a piece of ice float on water ?
Answer:
FLOATATION OF ICE ON WATER : Density of 0.9 g Cm-3 is less than density of water 1 g Cm-3. Hence, ice floats on water.

Question 22.
Explain why an iron needle sinks in water, but a ship made of iron floats on water.
Answer:
Density of iron is more than density of water, ∴ weight of iron nail is more than wt. of water displaced by it and nail SINKS. While shape of iron ship is made in such a way that it displaces MORE WEIGHT OF WATER than its own weight. Secondly the ship is HOLLOW and THE EMPTY SPACE contains AIR which makes the AVERAGE DENSITY OF SHIP LESS THAN THAT OF WATER and hence ship floats on water.

Question 23.
It is easier to swim in sea water than in river water. Explain the reason.
Answer:
Density of sea water is greater than density of river water, [because of impurities]
(i) In each case the weight of water displaced will be equal to the weight of the man.
∴ Ratio of weight of sea water and river water displaced by man is 1: 1.
(ii) With smaller portion of man’s body submerged in sea water, the wt. of sea water displaced is equal to the total weight of body. While to displace the same weight of river water, a larger portion of the body will have to be submerged ¡n water.
∴ It is easier for man to swim in sea water.

Question 24.
Icebergs floating on sea water are dangerous for ships. Explain the reason.
Answer:
ICEBERGS are very dangerous for ships as ICEBERGS are huge masses of ice floating in sea [density of ice being 0.917 g Cm-3]
with about 9/10 portion below water and only 1/10 portion of it above surface of water.

Question 25.
Explain why it is easier to lift a stone under water than in air.
Answer:
In water, the stone experience a buoyant force which counter balances the weight of the stone acting downward and this makes the stone lighter and thus easier to lift the stone in water.

Question 26.
What is a submarine ? How can it be made to’dive in water and come to the surface of water.
Answer:
SUBMARINE: Submarine is a water-tight boat which can travel under water like a ship. It is providgd with water tanks. When submarine is to dive, water is filled in water tanks and it is made heavier and average density of submarine becomes greater than the density of sea water and it sinks. To make the submarine rise to the surface of water, water tanks are emptied and average density.of submarine becomes less than the density of sea water and it rises to surface of water.

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 15

While submarine is underwater soldiers can see the enemy activities through periscope.

Question 27.
A balloon filled with hydrogen rises in air. Explain the reason.
Answer:
A balloon filled with hydrogen rises to a certain height as it displaces more wt. of air than wt. of balloon but as it rises higher density of air DECREASES there and upthrust becomes less and ultimately upthrust becomes equal to the weight of balloon and balloon stops rising further.

C. Numericals

Question 1.
The density of air is 1.28 g/Iitre. Express it in:
(a) g cm3 (b) kg m
Answer:
(a) The density of air is I .28g/litre
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 16
Question 2.
The dimensions of a hail are 10 m × 7 m × 5 m. If the density of air is 1.11 kg m-3, find the mãss of air in the hail.
Answer:
The dimensions of hall 10m × 7m × 5m
i.e. V350 m3
Density of air(D)= 1.11 kg m-3
M = V × D 350 ×  1.11 =388.5 kg

Question 3.
The density of aluminium is 2.7 g cm3. Express it in kg m-3
Answer:
Density of aluminium = 2.7 g/Cm3

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 17
Question 4.
The density of alcohol is 600 kg m-3. Express it in g Cm-3.
Answer:
Density of alcohol is = 600 kg/m-3

Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 18
Question 5.
A piece of zinc of mass 438.6 g has a volume of 86 Cm3. Calculate the density of zinc.
Answer:

Mass of Zinc (M) = 438.6 g
Volume V = 86 Cm3
Density (D) = ?
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 19
Question 6.
A piece of wood of mass 150 g has a volume of 200 Cm3. Find the density of wood ¡n
(a) C.GS. unit, (b) S.l. unit
Answer:
(a) Mass of wood (M) = 150 g
Volume of wood (V) = 200 Cm3
Density (D) =?
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 20
(b) In S.I. system = 0.75 × 1000 750 kg/ m3

Question 7.
Calculate the volume of wood of mass 6000 kg if the density of wood is 0.8 g Cm-3
Answer:
Volume of wood (V) = ?
Mass of wood (M) = 6000 kg
Density of wood D = 0.8 g/ Cm3
D=O.8g/Cm3=o.8 × IOOO = 800kg /m3
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 21

Question 8.
Calculate the density of solid from the following data :
(a) Mass of solid = 72 g
(b) Initial volume of water in measuring cylinder = 24 ml
(c) Final volume of water when solid is completely immersed in water = 42 ml
Answer:
Mass of solid (M) = 72 g
Intial volume of water V1 = 24 ml
Final volume of water V2 = 42 ml
Volume of solid (V) = V2 – V1 = 42 – 24 = 18 Cm3
Density of solid (D) = ?
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 22
Question 9.
The mass of an empty density bottle is 21.8 g, when filled completely with water is 41.8 g and when filled completely with liquid it is 40.6 g. Find :
(a) the volume of density bottle
(b) the relative density of liquid
Answer:
Density of water is 1 g Cm3
∴ Volume of density bottle = weight of water in grams completely filling the bottle
(a) Volume of density bottle:
Mass of empty density bottle = M1 =21.8 g
Mass of bottle + water = M2  41.8 g
∴ Mass of water completely fih1ig the density bottle = M2 — M1
=41.8 —21.8
20g
But 1 g of water has volume = 1 cc
∴ Volume of bottle (density bottle) = volume of water =20 c.c. =20 ml
(b) The relative density of liquid:
Mass of 20 c.c. of liquid = (mass of density bottle + mass of 20 c.c of liquid- mass of density bottle)
= 40.6—21.8
= 18.8 g
Mass of 20 C.C of water = 20g
Relative density of liquid
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 23
Question 10.
From the following observations, calculate the density and relative density of a brine solution. Mass of empty density
bottle = 22 g
Mass of bottle + water = 50 g
Mass of bottle + brine solution = 54 g

Answer:
Mass of empty bottle, M1 = 22 g
Mass of bottle + water, M2 =50 g
Mass of bottle + brine solution, M3 =54 g
Mass of water = M2 — M1 =50—22=28 g
Mass of brine solution = M3 — M1 54—22 = 32 g
Density of brine solution = Mass of brine solution / Mass of water
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 24
Question 11.
The mass of an empty density bottlfe is 30 g, it is 75 g when filled completely with water and 65 g when filled completely with a liquid. Find :
(a) volume of density bottle,
(b) density of liquid, and
(c) relative density of liquid.
Answer:
Mass of empty density bottle (M1) =30 g
Mass of bottle + Water (M2) 75 g
Mass of liquid + Liquidx (M3)= 65 g
Mass ofwater=M2—M1=75—30=45 g
(a) Volume of density bottle = Mass of water 45 g
(b) Density of Iiquid x = ?
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 25
(c) Mass of water in the density bottle =75 — 30 = 45 g
∴ Volume of water in density bottle = 45 cc
and mass of equal volume of liquid in density bottle 65—30 = 35g
Selina Concise Physics Class 8 ICSE Solutions Chapter 2 Physical Quantities and Measurement 26

Selina Concise Chemistry Class 8 ICSE Solutions – Chemical Reactions

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Selina Concise Chemistry Class 8 ICSE Solutions – Chemical Reactions

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

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Selina Concise ICSE Solutions for Class 8 Chemistry Chapter 6 Chemical Reactions

Exercise – I

Question 1.
(a) Define a chemical reaction.
(b) What happens during a chemical reaction ?
(c) What do you understand by a chemical bond ?
Answer:
(a) Any chemical change in matter which involves transformation into one or more substances with entirely different properties is called a chemical reaction.
(b) A chemical reaction involves breaking of chemical bonds between the atoms or groups of atoms of reacting substances and rearrangement of atoms making new bonds to form new substances.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-1
(c) A chemical bond is the attractive force that holds the atoms of a molecule together, in a compound.

Question 2.
Give one example each of which illustrates the following characteristics of a chemical reaction:
(a) evolution of a gas
(b) change of colour
(c) change in state
Answer:
(a) When Zinc reacts with dil. sulphuric acid. Hydrogen gas is evolved, with an effervescence
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-2

(b) When blue coloured copper sulphate reacts with hydrogen sulphide gas, a black coloured substance copper sulphide is formed.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-3

(c) The reaction between hydrogen sulphide and chlorine (both gases) produces sulphur (solid) and hydrogen chloride (gas).
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-4

Question 3.
How do the following help in bringing about a chemical change?
(a) pressure (b) light
(c) catalyst (d) heat.
Answer:
(a) Some chemical reactions take place when reactants are subjected to high pressure.
e.g: Nitrogen and hydrogen when subjected to high pressure produce ammonia gas.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-5

(b) Some chemical reactions can take place in the presence of light. Ex. Photosynthesis.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-6

(c) A catalyst can either increases or decreases the rate of chemical reaction and some chemical reactions need a catalyst to change the rate of the reaction, in case it is too slow or too fast.

  1. Positive catalyst: When a catalyst increase the rate of reaction finely divided iron is used as a positive catalyst in the manufacturing of ammonia from hydrogen and nitrogen.
    selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-7
  2. Negative Catalyst: When a catalyst decreases the rate of reaction.
    Ex. Phosphoric acid act as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide.

(d) Some chemical reactions take place only in the presence of heat.
e.g. When lead nitrate is heated, it breaks into lead monoxide, nitrogen dioxide and oxygen.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-8

Question 4.
(a) Define catalyst.
(b) What are (i) positive catalysts and (ii) negative catalysts? Support your answer with one example for each of them.
(c) Name three biochemical catalysts found in the human body.
Answer:
(a) Catalyst: A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change during the reaction.

(b) (i) Positive catalyst: When a catalyst increases the rate of chemical reaction, it is called positive catalyst.
e.g. when potassium chlorate heated to 700°C decomposes to evolve oxygen gas, when MnO2 is added the decomposition takes place at 300°C
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-9
(ii) Negative catalyst: When a catalyst decreases the rate of chemical reaction it is called negative catalyst.
Example. Phosphoric acid acts as a negative catalyst to decrease the rate of the decomposition of hydrogen peroxide. Alcohol too acts as a negative catalyst in certain chemical reactions.

(c) Biochemical catalysts found in human body:

  1. Pepsin
  2. Tryspin
  3. lipase.

Question 5.
What do you observe when
(a) dilute sulphuric acid is added to granulated zinc?
(b) a few pieces of iron are dropped in a blue solution of copper sulphate?
(c) silver nitrate is added to a solution of sodium chloride?
(d) ferrous sulphate solution is added to an aqueous solution of sodium hydroxide.
(e) solid lead nitrate is heated?
(f) when dilute sulphuric acid is added to barium chloride solution ?
Answer:
(a) When Zinc reacts with dilute sulphuric acid, hydrogen gas is evolved with an effervesence.
Zn + dil. H2SO4 → Zn SO4 + H2.

(b) When a few pieces of iron are dropped into a blue coloured copper sulphate solution, the blue colour of the solution fades and eventually turns into green.

(c) When a solution of silver nitrate is added to a solution of sodium chloride, white insoluble ppt. of silver chloride is formed.
AgNO3 (aq) + NaCl (aq) → AgCl (ppt) + NaNO3 (aq)

(d) When ferrous sulphate solution is added to sodium hydroxide solution, a dirty green ppt. of ferrous hydroxide is formed.
FeSO4 (aq) + 2NaOH (aq) → Fe(OH)2 ↓ + Na2SO4(aq)

(e) When solid lead nitrate is heated, it decomposes to produce light yellow solid lead monoxide, reddish brown nitrogen dioxide gas and colourless oxygen gas.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-42

(f) When few drops of dilute sulphuric acid is added to barium chloride solution, a white precipitate of barium sulphate is formed.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-43

Question 6.
Complete and balance the following chemical equations:
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-12
Answer:
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-13
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-14

Exercise – II

Question 1.
1. Fill in the blanks.
(a) A reaction in which two or more substances combine to form a single substance is called a combination reaction.
(b) A catalyst is a substance which changes the rate of a chemical reaction without undergoing a chemical change.
(c) The formation of gas bubbles in a liquid during a reaction is called effervesence
(d) The reaction between an acid and a base is called neutralization reaction.
(e) Soluble bases are called alkalis.
(f) The chemical change involving iron and hydrochloric acid illustrates a displacement reaction.
(g) In the type of reaction called double decomposition reaction, ions two compounds exchange their positive and negative radicals ions respectively.
(h) A catalyst either increases or decreases the rate of a chemical change but itself remains unchanged at the end of the reaction.
(i) The chemical reaction between hydrogen and chlorine is a combinaton reaction
(j) When a piece of copper is added to silver nitrate solution, it turns blue in colour.

Question 2.
Classify the following reactions as combination, decomposition, displacement, precipitation and neutralization. Also balance the equations.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-15
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-16

Question 3.
Define:
(a) precipitation (b) neutralization (c) catalyst
Answer:
(a) Precipitation: A chemical reaction in which two compounds in their aqueous state react to form an insoluble salt as one of the product.
Acid + Base → Salt + Water
Example.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-44

(b) Neutralization: A chemical reaction in which a base or an alkali reacts, with an acid to produce a salt and water only.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-18

(c) Catalyst: A catalyst is a substance that either increases or decreases the rate of a chemical reaction without itself undergoing any chemical change.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-19
here iron act as a catalyst and increases the rate of chemical reaction.

Question 4.
Explain the following types of chemical reactions giving two examples for each of them.
(a) combination reaction
(b) decomposition reaction
(c) displacement reaction
(d) double decomposition reaction
Answer:
(a) Combination reaction: A reaction in which two or more substances combine to form a single substance is called combination reaction.
A + B → AB
e.g (i) When iron and sulphur are heated together, they combine to form iron sulphide.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-20
(ii) When carbon bums in oxygen to form a gaseous compound called carbon dioxide.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-21
(b) Decomposition reaction: A reaction in which a compound breaks up due to the application of heat into two or more simple substances is called decomposition reaction.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-22
e.g. (i) Mercuric oxide when heated, decomposes to form two elements mercury and oxygen
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-23
(ii) CaCO3 when heated decomposes to calcium oxide and carbon dioxide.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-24

(c) Displacement reaction: A reaction in which a more active element displaces a less active element from a compound is called displacement reaction.
AB + C → CB + A
e.g. (i) Zinc, displaces copper from copper sulphate solution.
Zn + CuSO4 (aq) → ZnSO4 (aq) + Cu
(ii) Iron piece when added to copper sulphate solution, copper is displaced.
Fe + CuSO4 → FeSO4 + Cu.

(d) Double decomposition reaction: A chemical reaction in which two compounds in their aqueous state exchange their ions to form new compounds is called a double decomposition reaction.
AB + CD → CB + AD
e.g. (i) AgNO3 + HCl  AgCl + HNO3(aq)
(ii) NaOH (aq) + HCl (aq)  NaCl (aq) + H2O.

Question 5.
Write the missing reactants and products and balance the equations.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-25
Answer:
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-26

Question 6.
How will you obtain?
(a) Magnesium oxide from magnesium.
(b) Silver chloride from silver nitrate.
(c) Nitrogen dioxide from lead nitrate.
(d) Zinc chloride from zinc.
(e) Ammonia from nitrogen.
Also give balanced equations for the reactions
Answer:
(a) Magnesium when burnt in air (oxygen) Magnesium oxide is formed
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-27

(b) When silver nitrate solution reacts with sodium chloride, silver chloride is formed.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-28

(c) Lead nitrate when heated nitrogen oxide is obtained
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-29

(d) Zinc when reacts with hydrochloric acid zinc chloride and hydrogen (g) is formed.
Zn + 2HCl → ZnCl2 + H2

(e) Nitrogen when reacts with hydrogen at 450°C and under 200 atm, ammonia is formed.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-30

Question 7.
What do you observe when
(a) Iron nail is kept in copper sulphate solution for sometime.
(b) Phenolphthalein is added to sodium hydroxide solution.
(c) Blue litmus paper is dipped in dilute hydrochloric acid.
(d) Lead nitrate is heated.
(e) Magnesium ribbon is burnt in oxygen.
(f) Ammonia is brought in contact of hydrogen chloride.gas.
Answer:
(a) A brown layer of copper gets deposited on iron nail. This is due to chemical reaction.
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(b) Solution turns pink.
(c) Blue litmus turns red in an acid solution.
(d) The pale yellow solid is lead monoxide, the reddish brown gas is nitrogen dioxide and the colourless gas is oxygen.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-31
(e) Magnesium ribbon bums with a dazzling white light and produces a white powder which is magnesium oxide.
The reaction can be represented as
2Mg + O2 → 2MgO (white powder)
(f) Ammonia and hydrogen chloride, both compounds, combine to form a compound, ammonium chloride.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-32

Question 8.
Give reason:
(a) A person suffering from acidity is advised to take an antacid.
(b) Acidic soil is treated with quick lime.
(c) Wasp sting is treated with vinegar.
Answer:
(a) An antacid neutralizes stomach acidity.
(b) If the soil is acidic it can be treated with base like quick lime, to make it neutral.
(c) Wasp stings are alkaline and they can be neutralized by vinegar which is a weak acid.

Question 9.
What is meant by the metal reactivity series ? State its importance, (any two points).
Answer:
A list in which the metals are arranged in the decreasing order of their chemical reactivity is called the metal reactivity series.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-33
Special features of the activity series:

  1. The ease with which a metal in solution loses electron(s) and forms a positive ion decreases down the series, i.e. from potassium to gold.
  2. Hydrogen is included in the activity series because, like metals do, it too loses an electron and becomes positively charged (H+) in most chemical reactions.
  3. The series facilitates the comparative study of metals in terms of the degree of their reactivity.
  4. The compounds of the metals (oxides, carbonates, nitrates and hydroxides) too can be easily compared.

Question 10.
What are oxides ? Give two examples of each of the following oxides.
(a) Basic oxide (b) Acidic oxide
(c) Amphoteric oxide (d) Neutral oxide
Answer:
An oxide is a compound which essentially contains oxygen in its molecule, chemically combined with a metal or a non-metal.
selina-concise-chemistry-class-8-icse-solutions-chemical-reactions-34

Question 11.
Define exothermic and endothermic reactions. Give two examples of each.
Answer:
Exothermic reactions: The chemical reaction in which heat is given out is called exothermic reactions. It causes rise in temperature. .
e.g. (i) When carbon bums in oxygen to form carbon dioxide, a lot of heat is produced.
C + O2 → CO2 + heat.
When water is added to quicklime a lot of heat is produced which boils the water.
CaO + H2O → Ca (OH)2 + Heat.

Endothermic reaction: A chemical reaction in which heat is absorbed is called endothermic reaction. It causes fall in temperature.
e.g. (i) When nitrogen and oxygen together are heated to a temperature of about 3000°C, nitric oxide gas is formed.
N2 + O2 + heat → 2NO (g)
(ii) Decomposition of calcium carbonate into carbon dioxide and calcium oxide when heated to a 1000°C.
CaCO3 + Heat → CaO (s) + CO2 (g)

Question 12.
State the effect of:
(a) an endothermic reaction
(b) an exothermic reaction on the surroundings.
Answer:
(a) Carbon dioxide present in the atmosphere is trapped by infrared radiations, gives rise to temperature which is exothermic reaction.
(b) The melting of glaciers by global warming.

Question 13.
What do you observe when
(a) an acid is added to a basic solution.
(b) ammonium chloride is dissolved in water.
Answer:
(a) A chemical reaction in which a base or an alkali reacts with an acid to produce a salt and water.
Acid + Base → Salt + Water
(b) Dissolution of ammonium chloride in water is an endothemic reaction in which heat energy is absorbed.