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Selina Concise Biology Class 8 ICSE Solutions – Food Production

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Selina Concise Biology Class 8 ICSE Solutions – Food Production

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 9 Food Production. 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 9 Food Production

REVIEW QUESTIONS

Multiple Choice Questions:

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

(i) Which one of the following is an indigenous breed of dairy cows ?

  1. Jersey
  2. Frieswal
  3. Sahiwal
  4. Dangi

(ii) Which one of the following is the common breed of buffalo found in Gujarat ?

  1. Surti
  2. Murrah
  3. Gir
  4. Mehsana

(iii) Identify the indigenous breed of poultry of India:

  1. White leghorn
  2. HH-260
  3. Aseel
  4. B-77

(iv) Which one of the following is a rabi crop

  1. Mustard
  2. Pea
  3. Rice
  4. Wheat

(v) Identify the Kharif crop:

  1. Barley
  2. Mustard
  3. Rice
  4. Wheat

(vi) One of the following is a bacterial disease of sheep and goat. Identify it.

  1. Sore mouth
  2. Rinderpest
  3. Goat pox
  4. Brucellosis

(vii) Which one of the following is a bacterial disease of cattle in which the animal gets swelling on body parts, especially on the neck ?

  1. Cow pox
  2. Anthrax
  3. Salmonellosis
  4. Rinderpest

(viii) The plants that live for more than two years are called:

  1. Annuals
  2. Perennials
  3. Biennials
  4. Triennials

(ix) Which one of the following is a viral disease of poultry?

  1. Ranikhet disease
  2. Cholera
  3. Coryze
  4. Aspergillosis

Short Answer Questions:

1. Fill in the blanks:

  1. Cattle feed made from cereals and wheat is called concentrates.
  2. Rearing of birds for egg and meat is called poultry.
  3. Animal food is rich in proteins.

2. Name the following:

  1. The popular indigienous breed of poultry of India …..
  2. Rearing of honey bee …..
  3. Architect of white revolution in India …..
  4. A kashmiri goat which gives expensive wool ….
  5. Scientist responsible for green revolution in India ……

Answer:

  1. The popular indigienous breed of poultry of India Aseel.
  2. Rearing of honey bee is called apiculture.
  3. Architect of white revolution in India Mr. Verghese Kurien.
  4. A kashmiri goat which gives expensive wool kashmiri pashmina.
  5. Scientist responsible for green revolution in India M.S. Swaminathan.

3. Match the columns

Selina Concise Biology Class 8 ICSE Solutions - Food Production 1

Answer:

Selina Concise Biology Class 8 ICSE Solutions - Food Production 2

4. Answer the following questions:

Question 1.
Name any four animals which provide us food.
Answer:
Buffalo, goat, pig, hen, fish give us food.

Question 2.
Name any two dual purpose breeds of cattle.
Answer:
Dangi and Tharparkar are dual purpose breeds of cattle.

Question 3.
Give two examples of milch animals.
Answer:
Cows, buffaloes, goat are milk yielding animals.

Question 4.
Name any two high-yielding indigenous breeds of cow.
Answer:
Gir, Sahiwal, Red sindhi are high yielding breeds of cow.

Question 5.
Name four varieties of edible fishes of India.
Answer:
Eel, Hilsa, Salmon, Sardine, Pomphret are edible fishes.

Question 6.
Name two breeds of buffaloes.
Answer:
Murrah, surti, mehsana are breeds of buffaloes.

Question 7.
Name any two diseases of cattle caused by viruses.
Answer:
Cow pox, foot and mouth disease.

Question 8.
Name any two bacterial iiseases of cattle.
Answer:
Anthrax and rinderpest are bacterial diseases of cattle.

Question 9.
What are the symptoms of foot and mouth disease ?
Answer:
Blisters on the foot and mouth, high body temperature, reduced appetite are symptoms of foot and mouth disease.

Question 10.
Name two bacterial diseases of poultry.
Answer:
Fowl cholera, salmonellosis, coryze are bacterial diseases.

5. Briefly explain the following terms:
Answer:

  1. Animal husbandry: The branch of Biology which deals with feeding, shelter, caring and breeding of domesticated animals is called animal husbandry.
  2. Sericulture: Artificial rearing of silk worm and getting of silk from the silk worms is called sericulture.
  3. Aquaculture: The production and farming of aquatic animals as fishes, prawns, shrimps, molluscs, lobsters etc. is called aquaculture.
  4. Hatcheries: We raise small nurseries where water is stored in small pits where we put fish seeds (fish eggs). From these fish eggs very small fish come out after hatching. Then these small fish are transferred to big ponds. These small nurseries where eggs hatch to give small fish are called hatcheries.
  5. Pisciculture: It deals with production and management of fishes. It is a scientific, systematic way of raising of fishes, their multiplication, their production and management. So it is used as food in a sensible way.

6. What is organic farming?
Answer:
Organic farming is the practice of raising crops without using inorganic fertilisers and pesticides. Farmers use organic manure that has been prepared scientifically. In order to maintain soil fertility, and for weed and pest control, they use a combination of crop rotation, hand weeding, mixed cropping and biological control.

Long Answer Questions:

Question 1.
Differentiate between an egger and a broiler.
Answer:
Following are the differences between the egger and the broiler:
Egger

  1. Egg laying chickens are called eggers or egg layers.
  2. The chicks are given calcium (bones, seeds) and are reared to produce eggs.
  3. Eggers should give large number of eggs as white leghorns give many eggs. Rhode island red breeds like HH-260, IBL-80, B-77.

Broiler

  1. Chickens which give us meat are called broilers.
  2. Those chicks are reared on a diet of fats so that they gain flesh on their body and these are used as broilers.
  3. Broilers should give flesh. Indigenous variety Aseel give high yield of meat and less number of eggs.

Question 2.
Name any two exotic breeds of fowl in India, and mention their usefulness
Answer:
Exotic breeds of fowl in India are as:

  1. White leghorn: Its size is small and needs less feed for maintenance. So to raise it is economical. It lays oval white eggs.
  2. Rhode island red: It serves both the purposes as it is a good egg layer and also provide enough of meat. It was raised on a farm in Rhode island of U.S.A. So it is named as Rhode island red.

Selina Concise Biology Class 8 ICSE Solutions - Food Production 3

Question 3.
What are “milch animals”? Give three examples of exotic breeds of cow.
Answer:
Milk-producing animals are known as “milch animals” e.g. cows, buffaloes, goats and camels. The milk from goats is nutritious and is sometimes preferred to cow milk. But the production of goat milk is much less than that of cows and buffaloes. Cow milk is quite nourishing and easy to digest, but as compared to buffaloes, cows produce less quantity of milk. Buffaloes are the major source of milk in our country.
Exotic (Foreign) breeds. For example. Jersey, Holstein- Friesian, and Brown Swiss.

Question 4.
What is the meaning of the term “aquaculture”? Name any three animals which can be cultured by this method.
Answer:
The term “aquaculture” is used for production or farming of useful aquatic animals in various types of water bodies. The animals which can be cultured by this method are: fish, prawns, lobsters, molluscous, etc.

Question 5.
Differentiate between food crops and cash crops and give two examples of each:
Answer:
Differences:
Food crops

  1. These are crops which are grown for food such as cereals: wheat, rice, maize, pulses, oil seeds.
  2. These grow in the plains generally.
  3. These are annuals and complete their cycle in one season as in case of wheat, rice maize, gram, beans, peas.

Cash crops

  1. These are crops which are cultivated for commercial purposes such as tea, coffee, rubber, coconut, spices.
  2. These grow in the hilly areas on the slopes as water of rain should not stand in the roots as in case of tea.
  3. These plants are perennials. These plants live for more than two years. Tea, coffee require pruning before winter.

Question 6.
What are Kharif crops ? Give the name of the most important cereal plant of such crops. Briefly describe any three methods for cultivation of Kharif crops.
Answer:
Kharif crops generally grow in rainy season. Rice is the most important cereal Kharif crop growing in India. It occupies the largest area in India. It needs rainfall from 150 to 200 cms. It requires flooded fields during its growth. It requires alluvial loamy soil.

Cultivation methods of Kharif crops:

  1. Broadcasting: After preparing the fields for growing the rice crop the seeds are thrown in the fields. This method is adopted in the areas where there is less of rain. The fields are not flooded with water. This method is being adopted in China and Japan.
  2. Dibbling: In this method seeds are dropped at regular interval in the furrows made by the plough.
  3. Transplantation: Here the seeds are soaked for 24 hours. The seeds get sprouted. Then these seeds are transferred to nurseries. Here the seeds grow and attain a height of 6” to 9” and then these seedlings are transferred to specially prepared flooded fields which have been properly ploughed. Then those seedlings start growing in the fields. Then the fields are watered and manured from time to time. Then the crop matures and ultimately for ripening they require a temperature ranging from 16°C to 20°C. When the crop become fully ripe and plants become golden yellowish, then the crop is harvested manually or with the help of combines.

Question 7.
Name the two main crop seasons of India. Give three examples of the crops grown during each season.
Answer:
The two main crops seasons in India are:

  1. Kharif season: The rainy season is from July to October and is known as the Kharif Season. The chief kharif crops are the milles, known as Bajra and Jowar, Paddy, Maize, Cotton.
  2. Rabi season: The winter season is from November to April and is known as rabi season. Wheat, Gram, Peas, Linseed and Mustard are important rabi crops.

Question 8.
List the uses of bacteria in the food industry.
Answer:
The bacterial action is involved in the following industrial processes.

  1. In the manufacture of vinegar, butter and cheese.
  2. The process of tanning hides in leather making and preparing sponges.
  3. The separation of flax and hemp fibres which are used for making linen cloth and ropes.
  4. Fermentation of green plants for the production of ensilage for animal food.
  5. Bacteria are used for forming lactic acid, vinegar, citric acid, and vitamins.
  6. For formation of antibiotics, serums and vaccines, vitamin B complex.

Question 9.
Name any one variety of edible mushrooms.
Answer:
White button mushroom (Agaricus bisporous) and paddy straw mushroom (Volvariella) the two varieties of edible mushrooms.
Five major steps in cultivation of the common edible mushroom are as below:

  1. Composting: The compost is prepared by mixing the following in certain proportions.
    • Wheat or paddy straw,
    • Chicken manure
    • Some organic and inorganic fertilizer
      This compost is kept at about 50°C for a week.
  2. Spawning: “mushroom seed” consisting of mycelium of the selected type of mushroom is introduced into the compost, and allowed to spread for a couple of days.
  3. Casting: A thin layer of soil is spread over the compost to give support to the mushroom and provide humidity. It also prevents quick drying of the compost and helps to regulate temperature.
  4. Cropping and Harvesting: The growth occurs in three stages:
    (a) Mycelium (a network of fibrous mass) grows within 2 to 6 weeks.
    (b) Tiny pin heads.
    (c) Button stage which grows bigger attaining marketable size.
    The full grown mushrooms are taken out.
  5. Preservation: Mushrooms are highly perishable. Their shelf life is increased by a variety of processes
    (a) Vacuum cooling
    (b) Giving gamma radiation and storing at 15°C
    (c) Freeze drying in a solution of citric acid, ascorbic acid and brine, etc.

Question 10.
Mention the benefits of “Green revolution” in our country.
Answer:
Green revolution: Knowledge of science has brought about manifold increase in the production of grains, pulses and other crops and led to green revolution. Factors leading to it are:

  1. development of high – yielding varities.
  2. development of early – maturing varities.
  3. disease – resistant varities.
  4. using of fertilizers and pesticides.
  5. development of drought – resistant and dwarf varities.

Dr. M.S. Swaminathan is known as the father of green revolution in India which has led to manifold increase in the production of wheat and rice using hybrid varities (wheat – Kalyan Sona and Sonalika, Rice – IR – 8 Padma, Jaya and Pusa 215, Maize – Ganga 101 and Rankit).

Question 11.
Mention the benefits of “White revolution” in our country.
Answer:
The benefits of “White Revolution” in our country:

  1. The purpose of this programme was to link the rural producer (dairy farmer) with the urban consumer.
  2. Rural farmer co-operatives were organized at the village level and connected to the urban consumer.
  3. It ensured that the dairy farmer got a major share of the price of milk which consumers pay.

The “Operation flood” ensured thre objectives:

  1. increased milk production
  2. strengthened the dairy farmer’s income.
  3. easy availability of milk at a fair price to all.

Question 12.
Write briefly the processes of

  1. wine (alcohol) making and
  2. bread making.

Answer:

The steps for making

  1. Wine (alcohol): Wine is usually made from grapes. The grapes are crushed and the juice is extracted. The juice contains sugar and wild yeast.The yeast ferments the sugar and gradually turns it into alcohol.
  2. Bread: Mix some flour and water with a small amount of sugar and yeast. This makes dough. Then leave the dough for an hour or so in a warm place. During this period the living yeast cells multiply and fermenting sugar to form alcohol give off carbon dioxide gas. The gas so produced makes the dough rise, more or less doubling its size. Then when you bake the dough in a hot oven: the heat kills the yeast and evaporates the alcohol.

Question 13.
Give any five features of good shelter for milch animals.
Answer:

  1. Animal shelter should be very clean, well ventilated and well-lit.
  2. Cattle should have proper sheds, so that animals are safe from rain, cold and heat.
  3. The floor should have a proper sloping so that urine and excreta can be disposed of easily.
  4. Animals should have proper feeding and drinking tubs.
  5. Animal shelter should be spacious and there should not be over crowding.
  6. It should have arrangements for clean fresh drinking water.
  7. The shelter should give protection from predators.
  8. Shelter should be located away from the residential areas and waste disposal sites.

Question 14.
What type of food you would suggest for cattle in order to get good quality of milk ?
Answer:s
Cattle should be given good quality type of food which is proper for their growth, development, health and for their maintenance. Animal food is feed.
This cattle feed has two types of substances.

  1. Roughage: The animals get roughage from hay (straw of cereals), berseem, cowpea, lucerne, silage, maize, bajra and other green plants.
    These plants generally provide fibrous substances and other minerals.
  2. Concentrates: These are rich in carbohydrates, proteins, fats, minerals, and vitamins, concentrates are given by.
    • Grains and seeds of bajra, maize, rye, gram, cotton, jowar, barley. These provide carbohydrates.
      Legume seeds and cotton seeds provide proteins and fats.
    • Oil cakes: These oil cakes are very good feed for the animals. These are formed from the remains of oil seeds after we get the oil from the seeds. We get oil cakes from the seeds of cotton, mustard.
    • Molasses are rich in proteins.
    • Wheat bran, rice bran, and gram bran also give concentrates.

Selina Concise Chemistry Class 6 ICSE Solutions – Air and Atmosphere

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Selina Concise Chemistry Class 6 ICSE Solutions – Air and Atmosphere

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.

Selina Class 6 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Chemistry Chapter 6 Air and Atmosphere

POINTS TO REMEMBER

  1. Air cannot be seen as it is transparent we only feel its presence when it blows.
  2. The thick layer of air around earth upto 320 km above the surface is called atmosphere.
  3. Air is a mixture of various gases, water vapours, which protects us from harmful rays of Sun. It consists of nearly 80% nitrogen, 20% oxygen.
  4. The components of air can be separated by simple physical means. Has no formula.
  5. N2 is inert gas, reduces the effect of O2 present in air, N2 is helpful in plant growth as it provides nitrates used by plant for formation of protein which is important nutrient for animals.
  6. Oxygen is supporter of combustion no burning is possible without O2 and no life is possible without it.
  7. CO2 is must for plant life, plants prepare their food taking CO2 from air. CO2 maintains temp, of earth and without CO2 our planet would be too cold.
  8. Ozone in the upper layers of atmosphere protects the earth from harmful ultraviolet rays of Sun.
  9. Air is useful in many ways : Acts as medium for propagation of sound, birds, insects to fly in air, air ships, aeroplanes to fly only must due to presence of air. Air helps in movement of yachts, parachutes, aircrafts etc. Air is must for animals and plants on earth and air dissolved in water for aquatic life.
  10. Respiration : Is a slow chemical process when O2 present in the inhaled air reacts with the digested food material in the body to release energy, CO2 and water. Sugar + Oxygen -> Carbon dioxide + Water + Energy.
    Breathing : The complete process in which air is inhaled and exhaled is called breathing.
  11. Combustion : Burning of substance in air completely producing CO2, heat and light.
  12. Photosynthesis : Preparation of food by green plants taking CO2 from air, water from soil in presence of sun light.
  13. Oxygen in air remains constant it is not depleted as plants during day time produce lot of O2 in air.
  14. Soil contains air trapped in between its particle and organisms living there breath this oxygen. Due to this earth worms come out of soil during heavy rains as water gets into the pores in the soil.
  15. Common pollutant of air are smoke, dust, coal, emitted by industries and automobiles.
  16. Gases like SO2, NO2 also pollute air as they form corresponding acids when they come in contact with water vapours in air and fall down in the form of acid rain with rain water.
  17. These pollutants reduce the visibility which lead to accidents, cause global warming.

EXERCISE-I

Question 1.
What is atmosphere ?
Answer:
The earth is surrounded by a thick layer of air called the atmosphere that extends upto a height of about 320 kilometres above the surface of the earth.

Question 2.
Why can’t we see air ?
Answer:
We can’t see air because it is colourless, odourless and transparent gaseous matter.

Question 3.
What is wind ?
Answer:
Fast moving air is called wind.

Question 4.
What would have happened if there would have been no atmosphere around the earth ?
Answer:
Without atmosphere life would not be possible as atmosphere protects us from harmful gases. We could not live without
air present in atmosphere. In absence of the atmopshere, the earth would get so cold at night that we would not be able to survive. No CO2 and N2 for plants without atmosphere.
P.Q. When water is heated, we see bubbles rising up. Why ?
Answer:
Water has a lot of air dissolved on it. This is what allows breathing to fishes and other aquatic beings. The solubility of gases decreases when the temperature is raised, and that is why the dissolved air bubbles out from the water.

Question 5.
Why is air called a mixture ? Give five facts in support of your answer.
Answer:
Air is a mixture because :

  1. Air has no formula, a mixture has no formula whereas compound has a formula.
  2. No energy changes are involved to form air from various gases.
  3. When air is formed out of its constituents no change in mass and no change in volume takes place.
  4. Properties of air vary from place to place and time to time. i.e. there is more CO2 in towns as compared to villages where more oxygen prevails as compared to towns.
  5. Components of air can be separated by simple physical methods.

Question 6.
What are the main components of air ? Write down the composition of three main gases present in air by volume.
Answer:
Main components of air are :
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 6 Air and Atmosphere 1
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 6 Air and Atmosphere 2

Question 7.
What do you observe when

(a) Ice cold water is filled in a glass tumbler.
(b) A burning candle is covered with an inverted jar.
(c) Carbon dioxide gas is passed through lime water.
(d) A beam of light is allowed to enter in a closed dark room through a small hole.

Answer:

(a) We will observe that fine water droplets get deposited on the outer wall of the glass tumbler.
(b) The candle burn more brightly because candle gets oxygen support in burning.
(c) When CO2 gas is passed through lime water it forms calcium carbonate which is white precipitate (turbidity). This gives the milky white appearance to the solution.
(d) We will observe randomly moving dust particles in the beam of light. This confirms the presence of dust particles in the air.

Question 8.
Write the chemical name of –

(a) Lime water
(b) The white insoluble solid formed on reaction of carbon dioxide with lime water.

Answer:

(a) Calcium hydroxide Ca(OH)2
(b) Calcium carbonate – CaCO3

These droplets were present in air as moisture which got condensed on the cooler walls of glass tumbler. This shows the presence of water vapours in air.

EXERCISE-II

Question 1.
Name two important processes supported by oxygen present in air.
Answer:
Two processes supported by oxygen present in air are :

  1. Combustion
  2. Respiration

Question 2.
Give two uses of the following components present in air:

(a) oxygen
(b) nitrogen
(c) carbon dioxide
(d) water vapour

Answer:

(a) Oxygen: For respiration and breathing no life is possible without oxygen.
Oxygen is the most vital component which is responsible for two most important processes,
(i) Respiration and
(ii) Combustion.
(b) Nitrogen : Present in air gets fixed up in the soil as nitrates used by plants for their growth and for the formation of protein an important nutrient for animals. It is used to make fertilizers and various nitrogenous products.
(c) Carbon dioxide : Carbon dioxide is used by plants to prepare their food by photosynthesis. Dry ice (solid carbon-dioxide) is used as a refrigerant. Carbon dioxide is used to prepare fizzy drinks like soda water.
(d) Water vapour : Water vapors present in air provide moisture for both plants and animals. It also helps in predicting climatic conditions of a particular area as its amount varies from place to place and time to time.

Question 3.
Define the following:

(a) Respiration
(b) Photosynthesis
(c) Combustion.

Answer:

(a) Respiration : Respiration is a chemical process that takes place in all living beings (slow in plants). In this process, oxygen present in inhaled air reacts with the digested food material in the body. This results in release of energy, carbon-dioxide and water.
Sugar + Oxygen → CO2 + Water + Energy.
(b) Photosynthesis : Process of producing food by green plants taking CO2 from air, water from soil by roots and in presence of sun light and chlorophyll is called photosynthesis.
(c) Combustion : Combustion also called burning “is burning of substance in oxygen of air completely producing heat and light is called combustion.”

Question 4.
What are fuels ? Give two examples of modern fuels.
Answer:
Fuels : The substances which burn in air to produce large amount of energy in the form of heat and light are called fuels.
Examples :

1. CNG (Compressed natural gas)
2. LPG (Liquefied natural gas)

Question 5.
Give reasons :

(a) Aquatic animals and plants are able to survive in matter.
(b) A burning candle stops burning if covered with a glass tumbler.
(c) Mountaineers and divers carry oxygen cylinders with them.
(d) When water is heated, we see bubbles rising up.

Answer:

(a) Aquatic animals and plants use oxygen dissolved in water and survive.
(b) Oxygen is necessary for combustion when covered with a glass tumbler supply of oxygen stops.
(c) For artificial respiration mountaineers carry oxygen cylinders as at high altitudes, the air is thin and breathing becomes difficult. Also divers carry oxygen cylinder for artificial respiration as there is less oxygen dissolved in water (less dense) and breathing becomes difficult.
(d) These bubbles come from the air dissolved in water. The marine life uses air dissolved in water.

Question 6.
Name the processes which maintain the balance between oxygen and carbon dioxide in the air. How is it done?
Answer:
Respiration and combustion are the processes which maintain the balance between oxygen and CO2 in the air.

  1. Respiration : Respiration is a chemical process that takes place in all living beings. In this process, oxygen present in the inhaled air reacts with the digested food material in the body. This results in the release of energy, carbon dioxide and water.
  2. Combustion : Burning or combustion is a process in which a substance reacts chemically with oxygen and gets oxidised, with the release of energy in the form of heat and light. It is a fast process. During the process of burning, along with energy, carbon dioxide and water vapour are also produced.

Question 7.
State two similarities and two differences between respiration and burning.
Answer:
Similarities:
Burning

  1. Oxygen is needed to combine with carbon and hydrogen in compound.
  2. CO2 and H2O are formed with release of energy.

Respiration

  1. Oxygen is needed tocombine with C and H2 of food.
  2. CO2 and H2O are formed with release of energy.

Differences :
Burning

  1. It occurs at higher temperature.
  2. Is fast process.
  3. A natural and continous process.

Respiration

  1. It occurs at body temperature.
  2. Is slow process.
  3. An artificial & discont inuous process.

Question 8.
Define rusting ? What are the two necessary conditions for rusting of iron. Give the chemical name of rust.
Answer:
Rusting : Slow conversion of iron into its hydrated oxide in the presence of moisture and air is called rusting.
Conditions for rusting:

  1. Presence of moisture (water).
  2. Presence of oxygen (air).

Chemical name of rust is hydrated iron oxide [Fe20rxH20]

Question 9.
How is air useful to :

(a) water boats
(b) agriculture
(c) windmills
(d) scooters and cars.

Answer:

(a) Air helps movement of water boats.
(b) Air speeds up drying up of agricultural products like grains, pulses fruits etc. Air helps in pollination of flowers and dispersel of seeds.
(c) Windmills work where there is sufficient movement of air.
(d) Air filled tyres of cars move smoothly on road as there is less friction.

Question 10.
State the full form of LPG and CNG ? How are the two different in their composition ?
Answer:
LPG (Liquefied Petroleum Gas): It is obtained from crude petroleum oil. It mainly contains gaseous compounds known as isobutane and butane. Popularly it is known as cooking gas. It is the best fuel for domestic purposes and in laboratories. It is available in cylinders. It is also supplied through pipes in big cities.
CNG (Compressed Natural Gas): It is produced along with crude oil. It mainly contains methane gas. It has become a popular fuel for vehicles like three wheeler scooters, cars and buses. It is a cheap fuel as well as pollution free. It is used as a substitute of petrol.
Difference in composition
LPG is obtained from crude petroleum oil. It mainly contains gaseous compounds known as isobutane and butane. While
CNG is produced along with crude oil. It mainly contains methane gas.

Question 11.

(a) Why is nitrogen important to all living beings ?
(b) What is nitrogen fixation ?

Answer:

(a) Nitrogen constitutes 78% of air by volume. It is of vital importance to the plants, animals and human beings as it is needed to prepare vital nutrient ‘protein’ to every living being which is necessary for their growth.
(b) Nitrogen cannot be absorbed directly by plants. It is first fixed up in the soil as nitrites and nitrates and then absorbed by the plants in soluble forms. This phenomenon is called nitrogen fixation.

EXERCISE-III

Question 1.
What is air pollution ?
Answer:
Air Pollution : “Mixing of UNWANTED and HARMFUL SUBSTANCES in air is called AIR POLLUTION.”

Question 2.
Mention five causes of air pollution.
Answer:
CAUSES OF AIR POLLUTION ARE:

  1. Burning of FOSSIL FUELS and FIBRES.
  2. Cutting of forests.
  3. Erruption of volcanoes.
  4. Increase in POPULATION.
  5. Agricultural activities like use of chemical fertilisers, insecticides, pesticides and burning of husks etc.

Question 3.
Name two air pollutants which

(a) affect our health
(b) cause acid rain
(c) cause global warming.

Answer:

(a) Two air pollutants that affect our health are :

  1. DUST
  2. SMOKE

(b) Two air pollutants that cause acid rain are :

  1. SULPHUR DIOXIDE (SO2) and
  2. NITROGEN DIOXIDE (NO2)

(c) Two air pollutants that cause global warming are :

  1. CARBON DIOXIDE (CO2)
  2. METHANE (CH4)

Question 4.
What is meant by ozone depletion?
Answer:
Ozone is present in the upper layer of atomosphere called stratosphere. It protects the earth from harmful ultraviolet rays of the sun.
Some air pollutants like chlorofluorocarbon (CFC) react with ozone present in the atmosphere. These pollutants reduce the density of the air. The ultra-violet rays from the sun reach directly on the earth which affect human health, causing skin diseases and cancer and also increase the earth’s temperature.

Question 5.
State four steps to be taken to control air pollution.
Answer:
Four steps taken to control air pollution :

  1. Tall chimneys be installed in factories and power houses so that smoke and gases rise high and get diluted.
  2. GROW more tall trees to absorb CO2 Also plants help in bringing rains.
  3. Use unleaded petrol and CNG in all public transport vehicles
  4. Industries should be located far away from residential areas.

Question 6.
Name three greenhouse gases.
Answer:
Carbon dioxide, methane, nitrous oxide, etc.

OBJECTIVE TYPE QUESTIONS

1. Fill in the blanks

(a) The layer of air around the earth is called the atmosphere.
(b) Although we cannot see air, we can feel it.
(c) Air is a mixture of gases.
(d) Plants and animals maintain the balance of carbon- dioxide and oxygen in air.
(e) Polluted air is harmful for health.
(f) The supporter of combustion in air is oxygen.
(g) Green plants need CO2 water and light to prepare food.
(h) Oxygen is used in burning the food to get energy.
(i) Aquatic plants and animals use dissolved oxygen in water.
(j) The reddish brown powder on the surface of iron nails exposed to air and moisture is called rust.

2. Write ‘true’ or ‘false for the following

(a) Air is a compound.
Answer. False
Correct: Air is a mixture.

(b) Carbon dioxide is given out during photosynthesis.
Answer. False
Correct : Oxygen is given out during photosynthesis.

(c) Respiration needs nitrogen.
Answer. False
Correct: Respiration needs oxygen.

(d) The composition of air was discovered by Lavoisier.
Answer. True

(e) The major component of air is oxygen.
Answer. False
Correct: The major component of air is nitrogen.

MULTIPLE CHOICE QUESTIONS

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

1. Air consists of

  1. only oxygen
  2. only nitrogen
  3. only carbon dioxide
  4. all of these

2. Air pollution is due to the

  1. cutting of green plants
  2. gases like carbon monoxide, sulphur dioxide etc.
  3. smoke given out by factories
  4. all of the above

3. The gases which cause acid rain are

  1. sulphur dioxide and oxygen
  2. nitrogen and oxygen
  3. carbon dioxide and water vapour
  4. nitrogen dioxide and sulphur dioxide

4. Rust is

  1. hydrated iron oxide
  2. hydrated copper sulphate
  3. anhydrous iron oxide
  4. none of the above

5. Photosynthesis is a process in which plants

  1. take in oxygen and give out carbon dioxide
  2. take in carbondioxide and give out oxygen
  3. take in nitrogen and give out oxygen .
  4. none of the above.

6. Fuels which do not leave any residue on burning are

  1. coal and wood
  2. coal and LPG
  3. wood and CNG
  4. LPG and CNG

7. Respiration

  1. is a slow process
  2. is a natural and continuous process
  3. takes place at body temperature
  4. all of the above

8. Which of the following is common in combustion and respiration

  1. oxygen
  2. release of heat and light
  3. natural process
  4. nitrogen

9. Which of the following is not a green house gas ?

  1. carbondioxide
  2. sulphur dioxide
  3. methane
  4. nitrogen

10. The substance which accelerates the speed of a reaction without itself undergoing any change is called

  1. catalyst
  2. pollutant
  3. fuel
  4. none of the above.

Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Humans

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Selina Concise Biology Class 8 ICSE Solutions – Reproduction in Humans

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 3 Reproduction in Humans. 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 3 Reproduction in Humans

REVIEW QUESTION

Multiple Choice Questions:

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

(a) The testes are located within the:

  1. Penis
  2. Scrotum
  3. Ureter
  4. Urinary bladder

(b) Amoeba is most commonly reproduced by:

  1. Budding
  2. Regeneration
  3. Binary fission
  4. Multiple fission

(c) Identify the stage which is formed after the fertilisation of the egg by the sperm?

  1. Ovule
  2. Foetus
  3. Embryo
  4. Zygote

(d) Internally, the uterus opens into:

  1. Urethra
  2. Vagina
  3. Oviduct
  4. Vulva

(e) Which one of the following represents the correct sequence in the life history of a butterfly ?

  1. Egg → Larva → Adult → Pupa
  2. Egg → Pupa → Adult → Larva
  3. Egg → Larva → Pupa → Adult
  4. Egg → Pupa → Larva → Adult

Short Answer Questions:

Question 1.
Distinguish between the following pair of terms:
(a) Egg and sperm.
(b) Sexual reproduction and asexual reproduction.
(c) Budding and Regeneration.
Answer:
(a) Egg and sperm
Egg Sperm

  1. Egg is produced in the ovaries.
  2. Egg is spherical in shape with a nucleus.

Sperm

  1. Sperm is produced in the testes.
  2. Sperm has head with nucleus, middle piece and tail.

(b) Sexual reproduction and asexual reproduction.

Sexual reproduction

  1. In sexual reproduction the two sexes i.e., male and female produce special type of reproductive cells sperms in the male and eggs in the female.
  2. To produce a new individual the sperm has to reach the ovum and fuse with it. e.g. Humans, bird, reptile, etc.

Asexual reproduction:

  1. It involves the production of an offspring from a single parent without the fusion of reproductive cells (gametes).
  2. It is a rapid mode of multiplication, e.g. Lower plants and animals {Amoeba).

(c) Budding and Regeneration

Budding: Budding is a process in which buds grow on the outside of the parent body. The buds detach themselves when they are large enough.
Example: Hydra
Regeneration: Regeneration is the process that uses cell division to regrow lost body parts.
Example: Starfish, sponges

Question 2.
Define the following terms:
(a) Fetilization
(b) Implantation
(c) Puberty
Answer:
(a) Fetilization: When sperms and eggs from the opposite partners (males and females) fuse to form Zygote. It is called fertilization.
(b) Implantation: The fertilised egg (zygote) soon starts developing and by the time it reaches the uterus, a small ball of numerous cells is already formed. This is a kind of embryo which forms a pit in the wall of the uterus and gets fixed in it. This natural way of fixing of the embryo in the wall of the uterus is called implantation. This produces the state of pregnancy.
(c) Puberty: Puberty is the period during which the reproductive systems of boys and girls mature. In girls, it starts at the age of about ten and the first sign of puberty is the development of breasts. In boys, it starts at about 11 years of age of the^enlargement of the testes is its first sign. Sudden spurt in growth, shoulder girdle grows more than hip girdle.

Question 3.
State the reason why testes lie outside the abdomen in a scrotum?
Answer:
Both the testes remain in the scrotum because normal body temperature are to high, scrotum has smooth muscle tissues that keeps the testes at a cooler temperature than the body temperature 2°C to 3°C lower than the body temperature which is the most suitable temperature for sperm production.

Question 4.
Why is it important that a very large number of sperms should be present in the semen ?
Answer:
Single ejaculation of semen has 20,000,000 to 40,000,000 sperms. But only 1 or 2 sperms go into oviduct and fertilise the egg to form the Zygote. It forms embryo that forms an individual. It is the sperm in the semen that are of importance, and therefore semen quality involves both sperm quantity and quality.

Question 5.
List the structures, in their correct sequence, through which the sperms must pass from the time they are produced in the testes to the time they leave the urethra.
Answer:
Sperms are produced in testes. They pass as follows:
The testes consist of a mass of sperm producing tube. The tubes join to form ducts leading to the epididymis which in.turn leads into a muscular sperm duct. The two sperm ducts, one from each testes, open at the top of the urethra.

Question 6.
State the functions of the following:
(a) Ovary
(b) Testes
(c) Fallopian tubes
(d) Seminal vesicle
(e) Uterus
Answer:
(a) Ovary: Ovaries produce ova (eggs) and secrete female sex hormones, oestrogen and progestrone.
(b) Testes: A pair of testes are present in human male. The testes produce sperms.
(c) Fallopian tubes: There are two fallopian tubes in the human female reproductive system. Fertilization occurs in the fallopian tube. It also conveys fertilized egg to the uterus.
(d) Seminal vesicle: The function of seminal vesicle is to store sperms and to secrete seminal fluid.
(e) Uterus: The inner lining recieves, protects and nourishes embryo. Contractions of muscular wall expel baby during birth.

Question 7.
Given here is a section of the female reproductive system of human beings.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 1
(a) Name the parts labelled 1 to 4
(b) Name the part where fertilisation occurs in human beings.
Answer:
(a)

  1. Ovary
  2. Fallopian tube (Oviduct)
  3. Uterus (Inner lining or Muscular wall)
  4. Vagina

(b) Fertilisation occurs in the upper part of the oviduct. Sperm fuses withthe egg and zygote is formed this is called fertilisation.

Question 8.
Given alongside is a diagram of male reproductive system in humans. Label the parts indicated by numbers 1 to 5, and state their functions.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 2
Answer:

  1. Seminal vesicle: The seminal vesicles produce a secretion which serves as a medium for the transportation of the sperms.
  2. Prostate gland: Prostate gland which pours an alkaline secretion into the semen as it passes through the urethra.
  3. Testes: Sperms are produced in the testes.
  4. Urethra: Urethra passes through the penis and carries either urine or semen.
  5. Sperm duct: The sperm pass through the sperm ducts.

Long Answer Questions:

Question PQ.
Define the term metamorphosis. Briefly describe the various stages occurring in the life-cycle of a butterfly.
Answer:
Metamorphosis: A change in the form and often habits of an animal during normal development after embryonic stage complete transformation from an immature form to an adult form in two or more distinct stages.

Life cycle of butterfly: The butterfly lays its eggs on the leaves of the plants. The new born that comes out of the egg is called larva. It passes through various stages of development. The larva of butterfly is also called Caterpillar. It is very active. It is very voracious. It feeds and moves actively and gains size.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 3

It stops moving and eating and it is called pupa. It is a resting stage. The pupa spins thread around itself and thus is enclosed in a covering. It is called cocoon. This cocoon covers the pupa and is protective in function. During this stage it forms the features of an adult. After attaining adulthood the pupa comes out of the cocoon after breaking it as an adult butterfly. The wings of emerged butterfly are wrinkled and soft. After an hour these are fully stretched and it starts flying.

Question PQ.
What is fertilization? Describe the process in human beings.
Answer:
Fertilization: The fusion of male (sperm) and female (ova) gamete is called fertlization.

As the male performs sexual act with the female and as a result of it the semen is deposited in the vagina of the female. Thus the semen has millions of sperms. Only a few of these sperms are able to reach the upper part of the oviduct. If there is an egg in the oviduct it is fertilized by the sperm. As sperm enters the egg and this leads to the formation of zygote, this act is called fertilisation.

During fusion only the head part of the sperm, which has nucleus, enters the egg. The tail is left behind. The nucleus of the sperm and egg fuse and form the zygote. Soon this zygote becomes many called embryo and reaches the uterus and implants on the wall of the uterus and forms the foetus. Baby develops with in the gestation period of 280 days. After this the baby is delivered.

Question 1.
How does a single called fertilized egg grows into an adult in human beings?
Answer:
Fertilised egg i.e., zygote divides and redivides and forms a ball of cells. This is a kind of embryo and it reaches the uterus and gets attached to the wall of the uterus. This fixing of embryo to the uterus is called implantation. Now the embryo undergoes a process “specialisation of cells’’. It leads to the formation of different parts of the body. This process is called differentiation. It leads to the formation of various tissues and other organs and thus organ systems are formed. Organ system lead to the formation of an individual. Thus the zygote forms an embryo, it forms a baby and it forms an adult.

Question PQ.
Tabulate the important physical changes in the boys and girls that take place during puberty.
Answer:
Reproductive system of boys and girls mature during puberty. Puberty starts at 10 in girls and at 11 in boys. Testes enlarge in boys and breasts develop in girls. The following table shows the physical changed in boys and girls that take place during puberty.

Boys

  1. Testes become large
  2. Scrotal sac grows and penis becomes long.
  3. Length increases and shoulder girdle grows becomes more.
  4. Hair grow on the chest arm pits and on the sex organs.
  5. Facial hair and moustaches grow.
  6. Voice becomes hoarse and deep.

Girls

  1. Breasts become large.
  2. Ovaries become large and these release eggs. Size of uterus and vagina grows. Menstruation cycle starts.
  3. Sudden grow th takes place in length. Hip girdle becomes trough shaped, it larger than the shoulder girdle.
  4. Chest and abdomen do not have hair. But hair arise on the sex organs and the arm pits.
  5. No moustaches and facial hair.
  6. High pitch voice.

Question 2.
Describe the human female reproductive system with a labelled diagram.
Answer:
On each side of the uterus two white oval bodies lie. These are called ovaries. Eggs are produced in the ovaries. Nearer to the ovaries there lies expanded funnel shaped oviducts or fallopian tubes. The eggs go into the oviducts when released by the ovaries. The two oviducts open into the uterus. The walls of the uterus are muscular. The growing embryo lodges to the wall of the uterus. It is supplied by the food and blood through the placenta w hich is a connection betw een the growing embryo and the mother. The uterus joins the vagina. It is the vagina in which semen is lodged during sexual act. From here sperms go up into the oviduct and fertilise the egg. The urethra which brings urine from the urinary bladder opens into the.vulva just in front of the vaginal opening.
Selina Concise Biology Class 8 ICSE Solutions - Reproduction in Humans 4

Question PQ.
‘Adolescence is a crucial stage’. Justify this statement.
Answer:
During adolescence physical and emotional changes takes place in the body of boys and girls. This is period between the age of 10 to 19 and this is very critical period. Boys bear facial hair, muscular body, hair in the arm pits and on the sex organs, and have hoarse voice. The girls also have beautiful contours, raised breasts, wide lips and high pitch voice. The body increases in length in both cases. Boys and girls becomes conscious about the growth of the body. They become hesitant and shy to each other. They become body conscious and spend lot of time on dressing up and grooming. Hormonal level increases in their body and become restless.

Hormones affect their brains and control their emotions and moods. They cherish the company of their own sexes and show the attraction for the opposite sex. Thus it is very strange and crucial stage in their life. So adolescence is a very crucial stage in the life of the boys and the girls.

Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants

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Selina Concise Biology Class 8 ICSE Solutions – Transportation 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 1 Transportation 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 1 Transportation in Plants

REVIEW QUESTIONS

Multiple Choice Questions:

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

(a) Diffusion occurs when molecules move:

  1. from lower concentration to higher concentration.
  2. from higher concentration to lower concentration through a membrane.
  3. from higher concentration to lower concentration.
  4. when energy is used.

Answer: (3) from higher concentration to lower concentration.

(b) Ascent of sap in plants takes place through:

  1. Cortex
  2. Epidermis
  3. Xylem
  4. Phloem

Answer: (3) Xylem

(c) If the xylem vessels of a plant are plugged:

  1. The leaves will turn yellow
  2. No food will be made
  3. The plant will wilt (shrivel)
  4. The plant will continue to grow

Answer: (3) The plant will wilt (shrivel)

(d) Force responsible for the ascent of sap is:

  1. Capillary force
  2. Root pressure
  3. Transpirational pull
  4. All the three

Answer: (4) All the three

(e) Raisins swell when put in:

  1. Rain water
  2. Tap water
  3. Mustard oil
  4. Saturated sugar solution

Answer: (1) Rain water

(f) The root-hairs are suited for absorbing water from the soil because:

  1. They have a large surface area
  2. They have a semi-permeable membrane
  3. They contain a solution of higher concentration than the surrounding water.
  4. All the three.

Answer: (4) All the three.

(g) Transpiration is defined as:

  1. the rise of water up to the stem of a plant.
  2. the elimination of water with dissolved water products.
  3. the loss of water as water vapour from the aerial parts of a plant.
  4. the loss of water as water vapour from the roots as well as the leaves of the plant.

Answer: (3) the loss of water as water vapour from the aerial parts of a plant.

(h) Which one of the following favours the fastest transpiration rate ?

  1. A cool, humid, windy day,
  2. A hot, humid, windy day,
  3. A hot, humid, still day,
  4. A hot, dry, windy day.

Answer: (4) A hot, dry, windy day.

Short Answer Questions:

Question 1.
An experiment was set up as shown in the figure below. After some time, the Water level in test tube A fell down but not in test tube B.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 1
Why was there a fall in the water level of test tube A and not in that of test-tube B ?
Answer:
In test tube A the water level falls because the water was absorbed by the plant through its roots dipped in water. Here no water loss occurs due to evaporation from the water surface due to presence of oil.
In test tube B the water level remains unchanged as it does not contain a rooted plant. Due to the presence of oil on surface no water loss occurs due to evaporation.

Question 2.
How are roots useful to the plants? Give any two points.
Answer:
Roots are useful to the plants in the following way:

  1. It absorbs water and minerals from the soil and transport it upward to various parts of a plant.
  2. Roots fix the plant firmly in the ground.

Question 3.
What do xylem vessels carry?
Answer:
The xylem vessels carry the water and minerals absorbed by the roots to the stem and leaves.

Question 4.
Name the plant tissue which helps in carrying the food to different parts.
Answer:
Phloem.

Question 5.
Define the terms:
(a) semi-permeable membrane
(b) osmosis.
Answer:

(a) Semi-permeable membrane: It is a membrane that allows the movement of solvent molecules (e.g. water molecules) through it but prevents the movement of solute particles (e.g. sugar or salt molecules).
For example: Egg membrane, parchment membrane, cellophane paper etc. are semi-permeable membranes.

(b) Osmosis: The diffusion of water molecules through a semi-permeable membrane from a region where water is more concentrated to a region where it is less concentrated is called osmosis.
In other words, osmosis is the diffusion of water from its pure state or dilute solution into a stronger or concentrated solution through a semi-permeable membrane.

Question 6.
Under what conditions do plant transpire (a) more quickly and (b) most slowly?
Answer:
(a) Transpiration is faster on hot summer days as compared to cold winters.
(b) Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture (humidity).

Question 7.
Given here is an enlarged diagram of a part of the root. Draw arrows on the diagram to show the movement of water passing through different parts.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 2
Answer:
Path of water through the root hair to the xylem vessels.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 3

Question 8.
Why is the structure of the root hair is quite suitable for absorbing water from the soil ?
Answer:
The root hair are suitable for absorbing water from the soil in the following three ways:

  1. The root hairs present a large surface area. More the surface area, greater is absorption.
  2. The cell wall is of cellulose nature and forms permeable membrane and the plasma membrane around the vacuole forms the semi-permeable membrane.
  3. Root hairs have solution (cell sap) of a higher concentration than the surrounding soil water.

Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 4
Fig. Unicellular root hairs through the soil particles

Question PQ.
In an experimental set-up, a dye was placed at the bottom of a beaker filled with water as shown in figure A, below. After some time, the entire water in the beaker got coloured uniformly as shown in figure D.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 6
Answer:
(a) Name and define the phenomenon shown in the experiment.
Answer: The phenomenon is diffusion. Diffusion is the movement of the molecules or atoms of a substance (whether in a solid, liquid or gaseous state) from the region of higher concentration to the region of lower concentration.

(b) In all the four figures, two kinds of molecules are shown symbolically – larger and smaller. Which molecules are of the solute and which are of the solvent?
(a) Larger: ………… (b) Smaller: …………..
Answer: (a) The larger molecules are of the solute (dye)
(b) The smaller molecules are of the solvent (water)

(c) If all the dark shaded molecules in A are tightly enclosed in a cell membrane, what will be the nature of movement of the molecules, if any ?
Answer: As the concentration of solvent molecules is more in the left side of the figure A. The cell membrane will act as semi permeable membrane and will allow only the solvent molecules of water to move towards the solute particles. So the solvent molecules will move towards the solute particles. This will show the phenomenon or process of osmosis.

Question 9.
Briefly explain, how transpiration helps in upward conduction of water in plants? (a) ………… (b) ……………
Answer:
(a) Plants continuously absorb water through their roots. This water is sent up through the stem to all parts of the plant, including the leaves. Only a little amount, of water is retained in the plant or utilised by it in photosynthesis. The rest of it gets evaporated into the atmosphere as water vapour through the stomata present in the epidermis of the leaves and other aerial parts of the plant. This creates a suction pressure which pulls up water from xylem of the roots to the stem and then to the leaves.

(b) Xylem tissues are in the form of capillary tubes (tracheids and fibres) where narrower the diameter, greater will be the force. Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.
During day time, water is lost from the surface of the leaves by the process of transpiration. In this process, more and more water molecules are pulled up due to their tendency of rentainingjoined (cohesion). Such pulling force created by the leaves is very important in the case of tall trees where an upward conduction of water takes place.

Question 10.
How does temperature, light intensity and wind affect transpiration?
Answer:
Temperature: Transpiration is faster on hot summer days as compared to cold winters.
Light intensity: The transpiration rate is increased due to the increase in light intensity. During daytime in the sunlight, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion of carbon dioxide for photosynthesis. During dark, the stomata are closed, and hence transpiration hardly occurs at night.
Wind: Transpiration is more when the wind is blowing faster as water evaporates faster from the leaves.

Question 11.
The set up shown alongside was kept in sunlight for an hour. It was observed that drops of water appeared on the inside of the polyethylene bag.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 7
(a) Name the process which is being demonstrated.
(b) Why was the pot and its soil left uncovered by the polythene bag ?
(c) Why was the pot left in the sunlight?
(d) Suppose the pot in this experiment was placed inside a dark room instead of placing it in sunlight for some time. What difference will be noticed?
Answer:
(a) The process demonstrates the loss of water that has appeared in the polythene bag is transpiration.
As the potted plant covered with polythene bag is kept in the sunlight there will be loss of water through the stomata present on the leaves. The water drops will appear inside the polythene bag as a result of loss of water from the stomata. This is due to transpiration.

(b) As the potted plant is kept in the sun. The water vapours will also be given by the pot and the wet soil. These vapours (water drops) will also go inside the polythene if it covers the pot and the soil. We left the pot and soil uncovered by the polythene so that we may find the loss of water from the aerial parts of the plant covered with polythene bag. This shows that the water gets deposited in the polythene bag has come from the aerial parts of plant.

(c) As we keep the pot in the sunlight the stomata will open and the loss of water i.e., transpiration takes place from the aerial parts of the potted plant and the stomata. The loss of water will be more (transpiration) in the sun, and water vapours will appear in the polythene bag very soon.

(d) As we keep the pot inside the room, the stomata will not open fully and the rate of loss of water will be very-very less, and no water vapours will appear in the polythene bag. By keeping the pot in the room the loss of water will be very less and as a result the transpiration will be very less.

Question 12.
State whether the following statements are true or false. Rewrite the false statements correctly.
(a) Water absorption mainly occurs through the root-hair.
True
(b) Water enters the root-hair by osmosis.
True
(c) Water absorbed by the roots reaches the leaves and is used in producing food for the entire plant.
True
(d) A semi-permeable membrane allows larger molecules to pass through, but prevents the smaller ones.
False. A semi-permeable membrane allows smaller molecules to pass through, but prevents the smaller ones.
(e) Transpiration is the loss of water from the roots of the plant.
False. Transpiration is the loss of water from the aerial parts of the plant.
(f) Transpiration cools the plant when it is hot outside.
True
(g) During transpiration, the leaves lose more water from their upper surface.
False. During transpiration, the leaves lose more water from their lower surface.

Question 13.
Fill in the blanks with suitable terms given below: (Fast, Leaves, Stomata, Conducting, Ascent, Humid)
(a) Transportation in plants is carried out by a conducting system.
(b) The upward movement of sap that contains water and minerals is called ascent of sap.
(c) Transpiration is more when the wind is blowing fast.
(d) Most water gets evaporated from the plant from its leaves.
(e) Transpiration is reduced if the air is humid.
(f) The leaves have more stomata on their lower surface.

Long Answer Questions:

Question 1.
Draw a magnified view of the root-hair, and describe, how it helps in the absorption of water from the soil.
Answer:
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 8
Give above is a magnified view of a root-hair. It is a long protuberance of a cell. This cell contains a fluid called cell sap which is more concentrated than the surrounding soil water.
The root hair is covered by a very thin ceil membrane that allows water molecules to pass through, but prevents the larger molecules. So the water from the soil passes into the root hairs by osmosis.

Question PQ.
“Raisins swell in water, and grapes shrink in syrup.” Explain this phenomenon briefly.
Answer:
When we put some raisins in a bowl containing water, after 10-12 hours, we will notice that the raisins have swelled up. The raisins have absorbed water.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 9
But when we put some soft-skinned grapes in another bowl containing thick syrup of sugar. After 10-12 hours we will notice that grapes have shrunk. The grapes have lost water.
Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 10
In both cases the gain or loss of water is through the peel acting as a kind of semi-permeable membrane. This membrane has very minute pores which allow water molecules to pass through, but prevent the larger ones of sugar.

Question 2.
How does transpiration help the roots absorb water and minerals from the soil?
Answer:
Transpiration process in plants creates a suction pressure which pulls up water from xylem of the roots to the stem and then to the leaves.
Xylem tissues are in the form of capillary tubes (tracheids and fibres) where narrower the diameter, greater will be the force. Whenever the xylem vessels lay empty, such as during the loss of water by transpiration, the water from below rises into them by a capillary force.
Due to transpirational pull more and more water molecules are pulled up due to their tendency of remaining joined (cohesion). Such pulling force created by the leaves is very important in the case of tall trees where an upward conduction of water takes place.

Question 3.
Define the three processes by which plants absorb water and minerals from the soil.
Answer:
Following are the tree processes which help the plants to absorb water and minerals from the soil.

  1. Diffusion: Soil water moves into the root hairs through the process of diffusion from higher concentration to lower concentration as we put sugar in the milk and the sugar molecules are evenly distributed in the milk and occupy inter molecular spaces of milk.
  2. Osmosis: The cell sap and the cell walls act as semi- permeable membranes and permeable membranes. The concentration of the cell sap is more as compared to the water + minerals present in the soil. So the water and dissolved minerals enters the roots by the process of osmosis.
  3. Active transport: Root hairs absorb water and minerals from the soil. Water diffuses into the root hairs as the concentration of water is more as compared to root hair.
    But in case of minerals these move from lower concentration to molecules of higher concentration. So the minerals from the soil along with water move into the roots. So this is active transport in the opposite direction which needs energy.

Question 4.
How water absorbed by the roots is important for the plants?
Answer:
The water absorbed by the roots is important for the plant in three main ways:

  1. Transportation: The water in the plant body transports substances in solution from one part to another.
  2. Food production: Water is used in producing food (photosynthesis) by combining it with carbon-dioxide from the air in the presence of sunlight.
  3. Cooling: Water is used to cool the plant by evaporation through leaves when it is hot outside.

Question 5.
Name the factors which affect the rate of transpiration? State their role in each case.
Answer:
The following are the main factors that affect the rate of transpiration:

  1. Sunlight: During daytime, the rate of transpiration is faster. This is because the stomata remain open to allow the inward diffusion ofcarbondioxide for photosynthesis.
    During dark, the stomata are closed, and hence transpiration hardly occurs at night.
  2. Temperature: Transpiration is faster on hot summer days as compared to cold winter.
  3. Wind: Transpiration is more when the wind is blowing faster as water evaporates faster from the leaves.
  4. Humidity: Transpiration is reduced if the air is humid. Air cannot hold any water molecules when it is already laden with moisture (humidity).
  5. Low atmospheric pressure: The rate of transpiration increases when the pressure is low.

Question 6.
Mention the two ways in which transpiration helps the plants.
Answer:
Transpiration helps the plants in the following ways:

  1. Cooling effect: In transpiration, water gets evaporated from the plant. The heat required for this evaporation is obtained from the plant itself (latent heat) and thus the plant is able to cool itself w’hen it is hot outside.
  2. Transpiration helps in maintaining the concentration of the sap inside the plant body: The roots continue to absorb water from the soil. If excess water is not evaporated out, the sap would become dilute, preventing further absorption of water along with the minerals required by the plant.

Question 7.
Describe an experiment to show that the plant loses water through its leaves.
Answer:
Experiment: To demonstrate that the plants lose water through its leaves.

  • Take one small-sized, well-watered potted plant having a few branches. Place a polythene bag over its one branch as shown in A and tie it with a rubber band.
    Selina Concise Biology Class 8 ICSE Solutions – Transportation in Plants 11
  • Remove all the leaves from another branch (B) of the same plant, cover this too with a polythene bag and tie it with a rubber band.
  • Place the plant in sunlight, and observe it after 4-6 hours. You will notice that drops have appeared on the inner surface of the polythene bag over branch A, while no water drops appear on branch B.
  • This set-up indicates that most water gets evaporated from the plant through its leaves.

Question 8.
Name any three minerals whose deficiency causes diseases in plants. Give the symptoms of each deficiency.
Answer:
The nutrient elements i.e. minerals are essential for the plants to grow well and complete their life-cycle properly. The minerals are divided into two main categories:

(i) Macro-Nutrients: They are required in larger concentrations and they are obtained from soil.
The three macro-nutrients (minerals) whose deficiency causes diseases in plants are:

  1. Nitrogen (N) – Yellowing of leaves,wrinkling of cereal grains.
  2. Phosphorus (P) – Purple and red spots on leaves, delay in seed germination.
  3. Potassium (K) – Poor Growth

(ii) Micro Nutrients: They are required in small amounts and they are also obtained from soil.
The three micro-nutrients(minerals) whose deficiency causes diseases in plants are:

  1. Iron (Fe) – Yellowing of Leaves.
  2. Manganese (Mn) – Yellowing of leaves, with grey spots.
  3. Zinc (Zn) Desphaped leaves, yellowing of leaves, stunted plant growth.

Question 9.
List out the differences between xylem and phloem.
Answer:
The Xylem tissue consists of four types of cells:

  1. Tracheids: They are elongated dead cells with tapering ends. Their main function is in upward conduction of water and provide mechanical support.
  2. Vessels: They are like tube-like structures placed one above the other forming long channels. They provide mechanical support and also transport water and mineral salts laterally and vertically upward.
  3. Fibres: They are long, narrow and tapering at both ends. They provide only mechanical support.
  4. Parenchyma: They are living cells and helps in the conduction of water and minerals, and serve for the storage of food.

The Phloem tissue consists of four types of cells:

  1. Seive tubes: They are formed of seive cells and form the main conducting part of the phloem. These are cylindrical cells arranged in vertical rows, joined end to end. Their end walls are perforated by pores and are called seive plates. Seive piates helps in passing food material from cell to cell.
  2. Companion Cells: They are associated with seive tubes. It help sieve tubes in the conduction of food material.
  3. Parenchyma: It is formed of thin-walled unspecialized parenchymatous cells and these cells store food.
  4. Phloem fibres: They are dead sclerenchyma fibres formed of elongated cells. These provide mechanical strength.

Selina Concise Biology Class 8 ICSE Solutions – Endocrine System and Adolescence

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Selina Concise Biology Class 8 ICSE Solutions – Endocrine System and Adolescence

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 5 Endocrine System and Adolescence. 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 5 Endocrine System and Adolescence

REVIEW QUESTIONS

Multiple Choice Questions:

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

(a) Cortisone hormone is secreted by:

  1. Medulla of adrenal
  2. Cortex of adrenal
  3. Pancreas
  4. Thyroid

(b) Which one of the following hormones stimulates the breakdown of glycogen in the liver into glucose:

  1. Insulin
  2. Adrenaline
  3. Glucagon
  4. Thyroxine

(c) Which one of the following hormones converts excess of glucose into glycogen:

  1. Glucagon
  2. Thyroxine
  3. Insulin
  4. Adrenaline

(d) Which one of the following glands is also called master gland:

  1. Pituitary gland
  2. Adrenal gland
  3. Thyroid gland
  4. Ovary

(e) The emergency hormone to face the danger or to fight is secreted by:

  1. Islets of Langerhans
  2. Adrenal cortex
  3. Pituitary
  4. Adrenal medulla

(f) Which one of the following endocrine glands produces its hormone in large quantities as a result of emotional stimulation?

  1. Thyroid
  2. Islets of Langerhans
  3. Adrenal medulla
  4. Adrenal cortex

Adrenal medulla produces its hormone in large quantities as a result of emotional stimulation.

(g) In humans, increased thyroxine production results in (tick the correct answer):

  1. Increased metabolism
  2. Decreased metabolism
  3. Dwarfism
  4. Cretinism

Short Answer Questions:

Question 1.
What is a hormone?
Answer:
The secretions of the endocrine glands are called Hormones, which are poured directly into the blood and are carried to the target organs.

Question 2.
In table given below, fill in the blanks by naming endocrine glands, the hormones they secrete, and the function they perform, in a normal person.
Answer:

S.No. Name of the gland produced Function
1. Thyroid Thyroxine Control of metabolic rate
2. Pancreas Insulin Regulation of sugar in blood.
3. Adrenal Adrenaline and cortisone Preparing the body for action
4. Pituitary (i) Growth hormone
(ii) Thyroid stimulating hormone		 (i) For growth
(ii) Stimulates thyroid gland to secrete thyroxine

Question 3.
Match the items in Column A with those in Column B. Column A Column B
Selina Concise Biology Class 8 ICSE Solutions – Endocrine System and Adolescence 1

Answer:

Selina Concise Biology Class 8 ICSE Solutions – Endocrine System and Adolescence 2

Question 4.
Name the source and the function of each of the following hormones:

Hormone Source Function
(a) Glucagon
(b) Thyroxine
(c) Adrenaline
(d) Insulin
(e) Cortisone

Answer:

Hormone Source Function
(a) Glucagon Pancreas Breakdown of glycogen to glucose. Raises sugar in the blood.
(b) Thyroxine Thyroid gland Control of metabolic rate
(c) Adrenaline Adrenal gland Prepare the body to face emergency, stress
(d) Insulin Pancreas Regulation of sugar in blood.
(e) Cortisone Adrenal cortex Regulates carbohydrate metabolism. Its deficiency causes Addison’s disease.

Question 5.
What is the difference between an exocrine gland and an endocrine gland?
Answer:
The salivary glands, pancreas, etc., are exocrine glands, they send their secretions through ducts directly to the target orgOn the other hand, the endocrine glands are ductless glands. Their secretions are called hormones, which are poured directly into the blood and are thus carried to the target organs.

Question 6.
Why is pitnitary gland is called “master gland”?
Answer:
The pituitary gland is called “master gland” because it produces hormones that control other glands and many body functions including growth (growth hormone, Thyroid and Gonad stimulating hormone).

Question 7.
Briefly write about the importance of physical hygiene during adolescence.
Answer:
Physical hygiene also named as Personal hygiene plays a crucial role in maintaining healthy during adolescence. The teenager should follow the below mentioned activities to promote their health:

  1. Proper and Safe Food: Adolescence is a stage of rapid growth and development. Hence, a teenager should take proper care of their diet. They should take proper balanced diet that provides protiens, carbohydrates, fats, minerals and vitamins. They should take freshly prepared food and avoid stale food. They should take milk, fruits and fresh vegetables.
  2. Proper life Style: Regular Exercise and sleep are necessary for maintaining good health. Teenager should avoid long hours of continous table work, television watching. Teenager should not consume alcohol, drugs or smoking.
  3. Cleanliness: Teenager should take bath regularly. They should always wash their hands before and after having meals. Brushing up teeths after every meal. They should always change and wear washed clothes especially undergarments. Regular toilet habits should be adopted for maintaining good health. Teenager must keep their feet cleaned and protected. Injuries due to bacteria like tetanus, hookworms and insects may be issued if barefoot walk is undertaken. They must wash and comb their hairs regularly. All body parts must be washed and cleaned everyday. If cleanliness is not maintained there may occur chances of catching bacterial infection. Girls should take special care of cleanliness during the time of menstrual period.
  4. Physical Exercise: Inorder to keep the body fit and healthy, teenager’s should walk, exercise and play outdoor games regularly in fresh air. Playing Outdoor games reduces the stress and strain of adolescence.

Question 8.
Briefly discuss any four activities which can be practiced to overcome stress.
Answer:
Stress is a state of mental or emotional strain and in simple terms it is called as tension.
The stress can be controlled or reduced by following the below mentioned steps:

  1. Yoga: It is a mind-body practice that combines physical poses, controlled breathing, and meditation or relaxation. Yoga helps in reducing steps by:
    (a) Increasing Flexibility
    (b) Increasing muiscle strength and tone.
    (c) Improving respiration, energy and vitality.
  2. Exercise: Exercise or Running or Jogging for 30 to 45 minutes at least three times a week reduce stress and keep’s the body much healthier.
  3. Proper sleep schedule: Improving your sleep schedule also helps in reducing the stress.
  4. Reading is a great way to calm your mind and to gain more knowledge.
  5. Practice Hobbies of your interest: One should must keep practicing their hobbies as it helps in reducing the stress. Enjoy playing guitar, paino or listening music or doing riddles.

Selina Concise Chemistry Class 6 ICSE Solutions – Elements, Compounds, Symbols and Formulae

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Selina Concise Chemistry Class 6 ICSE Solutions – Elements, Compounds, Symbols and Formulae

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.

Selina Class 6 Chemistry ICSE SolutionsPhysicsBiologyMathsGeographyHistory & Civics

Selina Concise ICSE Solutions for Class 6 Chemistry Chapter 4 Elements, Compounds, Symbols and Formulae

POINTS TO REMEMBER

  1. Pure substances : “A single substance of definite composition.” Pure substances are homogeneous. They are made up of only one kind of atoms and compounds or made up of only one kind of molecules.
  2. Elements : An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process.
  3. Metals : Most of the elements known to us are metals. Example: Sodium potassium, iron, gold, silver are elements. Metals are lustrous, hard, ductile and malleable, good conductor of electricity. Mercury (liquid) have High M.P. and High B.P. but exceptions are there.
  4. Non-metals : Carbon, phosphorous, sulphur all solids, Bromine (liquid) iodine(s) and rest are gases, dull, do not shine. Cannot be drawn into wires, non malleable, have low M.P. and B.P. do not produce sound when struck, do not conduct electricity. Exceptions are there.
  5. Boron, sillicon, arsenic, antimony resemble both metals and non-metals and are called metalloids.
  6. Unreactive gases, also called noble gases are gases which are very unreactive i.e. He, Ne Ar, Kr, xenon and radon.
  7. Symbols are abbreviations that are used to denote a chemical element which is usually first letter of its name in English or Latin.
  8. O is the symbol of element oxygen.
    C is symbol of element carbon.
    Cu is symbol of element copper (taken from Latin name Cuprum)
  9. Compound is formed by the chemical combination of two or more elements in definite ratio (by mass).
  10. Molecule is the smallest unit of a compound.
  11. Elements are the basic substances from which all other substances are made.
  12. Compound : Consist of two or more elements combined in definite proportion, pure and homogeneous, physical and chemical properties are entirely new and different from its consititutent elements, energy is either needed or produced when a compound is formed.
  13. Atoms : Atom is the smallest unit of an element which cannot be further broken into simpler parts, may or may not have independent existence.
  14. Molecule of element : When two or more atoms of the same element combine it forms a molecule of an atom. e.g. N2,O2
  15. Molecule of compounds : When atoms of two or more element combine, they form a molecule of a compound. H20, HC1, CuSO4.

EXERCISE-I

Question 1.
Classify the following substances into elements and compounds.
Answer:
Mercury, sulphur, sugar, water, sand, gold, coal, oxygen, alcohol.
Ans. Element: Mercury, sulphur, gold, coal, oxygen.
Compound : Sugar, water, sand, alcohol.

Question 2.
Give the symbols of: Carbon, calcium, copper, chlorine, cobalt, argon.
Answer:
Carbon is C         Chlorine is Cl
Calcium is Ca     Cobalt is Co
Copper is Cu       Argon is Ar

Question 3.
Define a pure substance. How many types of pure substances do you know ?
Answer:
Pure substances : “A substance of a definite composition which has consistent properties throughout, is called a pure substance”
Types of pure substances: Pure substances are of two types (i) Elements, (ii) Compounds.

Question 4.
Define : (a) Elements (b) Compounds.
Name the particles from which elements and compounds are made of.
Answer:
(a) Elements : An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process.
(b) Compounds : Compounds are pure substances composed of two or more elements in definite proportion by mass and has a definite set of properties. Compound is made up of only one kind of molecules.

Question 5.
Give two examples for each of the following :
(a) Metals
(b) Non-metals
(c) Metalloids
(d) Noble gases
Answer:
(a) Metals : Iron, silver, gold.
(b) Non-metals : Carbon, sulphur, oxygen.
(c) Metalloids : Antimony, silicon, boron.
(d) Noble gases : Helium, argon, neon.

Question 6.
Name the elements which form water. How will you justify that water is a compound ?
Answer:
The elements which form water are (i) Hydrogen and oxygen.
Justification : Water has entirely different properties (i.e. is a liquid, extinguishes fire) from the elements it is made up of i.e. Hydrogen a gas catches fire oxygen a gas supporter of combustion.

  1. Energy is needed to form water on combining O2 with H2.
  2. We can not seperate the constituents of water by simple physical means.

Question 7.
Give three differences between metals and non-metals.
Answer:
Metals

  1. Metals are ductile i.e. can be drawn into wires.
  2. Metals are malleable i.e. can be beaten to form sheets.
  3. They are sonorous.

Non-metals

  1. Non-metals are mostly soft solids cannot be drawn into wires.
  2. They are mostly gases and are not malleable.
  3. They donot produce sound when struck.

Question 8.
How is sodium chloride different from its constituent elements, sodium and chlorine ?
Answer:
Sodium is a metal that is stored in kerosene oil as it reacts very fast with air and water. Chlorine is a reactive greenish yellow gas which is poisonous. When these two elements combine chemically they form common salt sodium chloride which is non poisonous colourless solid substance that we use in our food to add taste and to obtain some nutrition.

Question 9.
State four important characteristics of compounds.
Answer:

  1. When compound is formed energy like heat, light or electricity is either needed or produced.
  2. A compound has properties entirely different from the properties of its constituents.
  3. Change in weight takes place.
  4. It cannot be separated into its constituents by simple physical means.

Question 10.
Give two examples for each of the following :

(a) Non-metals which are solids
(b) Metals which are soft
(c) Non-metals which are lustrous
(d) Elements which are liquids.
(e) Inert gases
(f) Metalloids

Answer:

(a) Phosphorus, Sulphur
(b) Lead and Sodium
(c) Radium, Graphite
(d) Mercury, Bromine
(e) Helium, Neon
(f) Antimony, Arsenic

Question 11.
Name the elements present

(a) Sugar
(b) Ammonia
(c) Marble
(d) Washing soda

Answer:

Compounds
(a) Sugar
(b) Ammonia
(c) Marble
(d) Washing soda
Elements present
(a) Carbon, hydrogen & oxygen
(b) Nitrogen and hydrogen
(c) Calcium, carbon & oxygen
(d) Sodium, carbon & oxygen

Question 12.
What is the proportion of elements present in the following compounds?
(a) H2O
(b) CO2
(c) CaO
(d) NO2
Answer:
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 1

Question 13.
Name two compounds which dissolve in water.
Answer:
Two compounds which dissolve in water are sugar, table salt.

EXERCISE-II

(ATOMS & MOLECULES)

Question 1.
Define:

(a) Atom
(b) Molecule
(c) Atomicity
(d) Formula

Answer:
(a) Atom : An atom is the smallest indivisible unit of an element which exhibits all the properties of that element and may or may not have independent existence.
(b) Molecule : A molecule can be defined as the smallest unit of an element or a compound which exhibits all the properties of that element or compound and has independent existence. They are divisible into atoms.
(c) Atomicity : The number of atoms in a molecule of an element is called its atomicity.
(d) Formula : Formula is a short way of representing the molecule of an element or a compound.

Question 2.
Why are symbols and formulae of substances important?
Answer:
Importance of symbols and Formulae :
Symbols and formulae of substance gives a lot of information like.

  1. Types of elements present in the compound. E.g. (H20 is made of two elements hydrogen and oxygen).
  2. Number of each kind of atoms in one molecule. E.g. (water has 2 atoms of hydrogen combined with 1 atom of oxygen.)
  3. Mass of one molecule of the compound. E.g. [H2O has mass (1 × 2) + 16 = 18 g].

Question 3.
Mention three gaseous elements and write their molecular formulae.
Answer:
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 2

Question 4.
State the informations obtained from the formula of a compound.
Answer:
A formula gives us the following information about a compound.

  1. Types of elements present in the compound.
  2. Number of each kind of atoms in one molecule of the compound.
  3. Mass of one molecule of the compound.

Example:
A molecule of carbon dioxide gas is represented by CO2 It indicates that a carbon dioxide molecule is formed by the combination of two elements i.e. carbon and oxygen. The number of carbon atom is one and that of oxygen atom is two. The mass of one molecule of carbon dioxide can be calculated by adding the mass of one atom of carbon and two atoms of oxygen.

Question 5.
What is meant by
(a) 2H and H2
(b) H20 and 3H2O ?
Answer:
(a) 2H is two atoms of hydrogen. H2 is one molecule of hydrogen gas.
(b) H20 represents one molecule of water. 3H20 represents 3 molecules of water.

Question 6.
State the number of atoms of each kind, present in
(a) C6 H12O6
(b) H2SO4
(c) HNO3
(d) CaCO3
Also name these compounds.
Answer:
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 3

Question 7.
Write the molecular formulae of compounds calcium oxide, hydrogen sulphide, carbon monoxide and lead sulphide.
Answer:
Compound Calcium oxide is formed of elements calcium (Ca) and oxygen (O)
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 4
Symbols combining power Here subscript number is same Ca2 Formula of calcium oxide is CaO Compounds Hydrogen sulphide is formed of elements
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 5

EXERCISE-III

Question 1.
Name:
(a) Three different forms of carbon.
(b) A form of carbon used as a gem.
(c) Two substances used to make electric wires.
(d) Two substances used to make jewellery.
(e) A substances used as an insulator.
Answer:
(a)

  1. Diamond
  2. Graphite
  3. Coal

(b) Diamond is used as gem.
(c)

  1. Copper.
  2. Aluminium as these are good conductors of electricity.

(d)

  1. Gold.
  2. Silver as these are shining, lustrous, and ductile.

(e) Plastic is used as insulator as it is bad conductor of electricity.

Question 2.
Give one use of each of the following substances :

(a) Iron
(b) Brass
(c) Coal

Answer:
(a) Iron : To make machines tools and building material.
(b) Brass : To make water taps and utensils.
(c) Coal: Coal is used as fuel also used in thermal power plant to produce electricity.

Question 3.
Give reason:

(a) A frying pan is made up of steel but its handle is made up of wood.
(b) Graphite is used to make lead of the pencils.
(c) Argon is filled in electric bulbs.

Answer:

(a) Steel is good conductor of heat to cook food, pan is made of steel where as wood is insulator of heat and to hold, handle is made up of wood.
(b) Graphite leaves mark on the paper and makes it black.
(c) Argon is inert gas and protects the element of bulb from oxidation and burning. Hence increases bulb’s life.

Question 4.
Answer the following questions:

(a) Why are copper and aluminium used to make electric wires?
(b) What do you understand by the statement: ‘metals are ductile and malleable’?
(e) Give the advantages of using symbols instead of names of elements or compounds.
(d) When iron is mixed with sulphur at room temperature, it does not form a compound. Why?
(e) Find the atomicity of the Tollowing molecules:

  1. calcium chloride
  2. aluminium suiphide
  3. acetic acid
  4. dinitrogen oxide
  5. carbon monoxide

Answer:
(a) Copper and aluminium are good conductors of heat and electricity. They can be drawn into wires and beaten into sheets. Therefore, they are used to make electric wires.
(b) Metals are ductile, i.e., they can be drawn or stretched into thin wires. They are malleable, i.e., they can be beaten into thin sheets.
(c)

  1. Symbols increases scientific communication across the world.
  2. Symbols helps to make equations and data shorter and concise.
  3. Symbols are helpful for Scientists as it would take time and paper to do their job. They had to write out the full name of every element instead of its symbol.

(d) When iron is mixed with sulphur at room temperature, it does not form a compound because the mixture of iron and sulphur requires heat to form a compound i.e. iron sulphide.
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 6

OBJECTIVE TYPE QUESTIONS

1. Fill in the blanks

(a) Atomicity refers to the number of atoms in the molecule of an element.
(b) The most abundant element in the earth’s crust is oxygen.
(c) A metal which is a liquid at room temperature is mercury.
(d) The most abundant element in the atmosphere is nitrogen.
(e) A metal which is a poor conductor of electricity is tungsten.
(f) A diatomic gaseous element is oxygen.
(g) A liquid non-metal is bromine.

2. Match the columns
Selina Concise Chemistry Class 6 ICSE Solutions Chapter 4 Elements, Compounds, Symbols and Formulae 7

3. Indicate whether the following statements are true or false.

(a) A compound is made up of just one kind of atom.
Answer. True False
Correct : A compound is made up of two or more elements is a fixed proportion by mass.

(b) Metals reflect light and are good conductors of electricity.
Answer. True

(c) Metals can be polished.
Answer. True

(d) Elements are made up of compounds.
Answer. False
Correct : Elements are made up of atoms.

(e) All elements are artificially prepared.
Answer. False
Correct: All elements are made up of a limited number of basic substances.

(f) Molecules can exist independently.
Answer. True

(g) Molecules combine to form atoms.
Answer. False
Correct : Atoms combine to form molecule.

(h) Noble gases are high reactive.
Answer. False
Correct: Noble gases are non-reactive.

(i) Ozone is a triatomic molecule.
Answer. True

MULTIPLE CHOICE QUESTIONS

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

1. All pure substances have

  1. the same physical state .
  2. the same colour
  3. the same composition
  4. a definite set of properties

2. Sugar is a compound which consists of the elements

  1. carbon and hydrogen
  2. hydrogen and oxygen
  3. carbon, hydrogen and oxygen
  4. hydrogen, carbon and sulphur

3. Atoms of different kinds combine to form molecules of

  1. an element
  2. a compound
  3. a mixture
  4. all of the above

4. Sulphur and carbon are

  1. metals
  2. non-metals
  3. metalloids
  4. noble gases

5. Gold is used to make jewellery because

  1. it is dull
  2. lustrous and attractive
  3. highly reactive
  4. very cheap

6. The most abundant elements in the universe are

  1. neon and argon
  2. hydrogen and helium
  3. aluminium and copper
  4. oxygen and nitrogen

7. The compound used as common salt is

  1. sodium chloride
  2. calcium chloride
  3. sodium oxide
  4. hydrogen chloride

8. Brass and bronze are

  1. elements
  2. mixtures
  3. compounds
  4. all of the above

9. Sand is a compound of

  1. silicon and nitrogen
  2. silicon and oxygen
  3. oxygen and sulphur
  4. none of the above

10. From the list given below select the correct substance which is most suitable to the statements given : (oxygen, diamond, zinc, graphite, gold)

  1. A metal which is brittle.
  2. A non-metal which is a good conductor of electricity.
  3. The hardest naturally occurring substance.
  4. The most ductile metal.
  5. A gaseous non-metal.
    Answer.
    (a) Zinc
    (b) Graphite
    (c) Diamond
    (e) Oxygen

Selina Concise Biology Class 7 ICSE Solutions – Excretion in Humans

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Selina Concise Biology Class 7 ICSE Solutions – Excretion in Humans

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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 5 Excretion in Humans

Synopsis —

  •  The substances which should be excreted are :
    1. urea, uric acid
    2.  Bile pigments
    3. water
    4. extra salts such as sodium
    5. chloride extra vitamins.
  • The vitamins passed out into urine if in excess are vitamin B and C.
  •  The kidneys are situated towards the back of the abdomen at the level of last two ribs.
  •  Right kidney is located at slightly lower level than the left kidney.
  • The ureters run from the kidney to the urinary bladder and urethra runs from urinaiy bladder to the exterior.
  • Accessory excretory organs are
    1.  skin
    2. lung
    3. liver
  •  The main function of the skin is to cool the body.
  •  Liver converts highly toxic ammonia produced in the body to less toxic urea.
  •  Liver eliminates cholesterol, bile pigments, extra vitamins, and many durgs.
  •  The amount of urine produced by the glomerular filtrate after reabsorption per day is 1.2 litre.

(Review Questions)

MULTIPLE CHOICE QUESTIONS :
1. Put a tick mark (✓) against the most appropriate alternative in the
following statements :

(i) The kidneys are made up of tiny tubular units called :
(a) glomerulus
(b) nephrons
(c) capillaries
(d) neurons

(ii) In human beings, urea is produced in :
(a) liver
(b) kidney
(c) spleen
(d) urinary bladder

(iii) Besides water, the urine mainly contains :
(a) urea
(b) nitric acid
(c) glucose
(d) bile pigments

(iv) Filtration of excretory wastes from the blood occurs in:
(a) collecting tubule
(b) ureter
(c) urinary bladder
(d) nephrons

Short Answer Questions
1. Fill in the blanks :

  1. Nitrogenous wastes in the urine are in the form of urea and uric acid.
  2. The unit of human kidney is called nephron.
  3.  Evaporation of sweat from skin surface has cooling effect.

2. Define the following:
(i) Excretion:
(ii) Excretory organs :
(iii) Dialysis :
(iv) Nephron:
Ans.
(i) Excretion : During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
The process of removal of useless and harmful metabolic waste substances is called excretion.
(ii) Excretory organs : During different metabolic activities taking place in our body, the body produces many substances of which some are useful and some are useless.
If retained in the body the unwanted substances may become poisonous and cause much harm and in severe cases, even death. The organs which remove these unwanted and toxic substances from the body are called excretory organs.
(iii) Dialysis : The artificial process which cleans and filters the blood in a person where one or both the kidney may stop working properly is called dialysis.
(iv) Nephron : Inside the kidney, there are millions of microscopic tubes called renal tubules or nephrons. It is the structural and functional unit of kidney.

3. Write True (T) or False (F) for the following statements in the spaces provided. Rewrite the false statements in correct form.

  1. Removal of solid undigested food is excretion
    False
    Correct: Removal of solid undigested food is egestion.
  2.  Medulla of kidney passes urine into urinary bladder.
    False
    Correct: Medulla of kidney passes urine into funnel-like pelvis.
  3.  Excess sugar in blood is a symption ofdiabetes.
    True
  4.  Urine is devoid of blood cells.
    True

4. Name the blood vessel that brings blood to the kidneys.
Ans. Renal Artery

5. Where in the urinary system do the following processes take place ?
Ans.

  1. Urine formation: kidneys.
  2.  Transport of urine away from kidney: urethra.
  3.  Temporary storage of urine : urinary bladder.

Long Answer Questions

Question 1.
Define excretion. Write the four organs of human urinary system in their correct sequence.
Answer:
The process of elimination of unwanted and toxic products from the body is called excretion.
The four organs of the urinary system from above to downward are:

  1. kidneys
  2.  ureter .
  3. urinary bladder
  4.  urethera.

Question 2.
Why is excretion necessary in living beings ?
Answer:
The excretion is necessary because the toxic products if allowed to be retained in the body act as poison and cause great harm to the body. If they exceed the threshold, they may even cause death.

Question 3.
What is meant by osmoregulation ?
Answer:
The process of maintaining accurate concentration of water and salts in the body is called osmoregulation.
This is done by the kidneys.

Question 4.
Describe the structure of kidney with the help of a labelled diagram.
Answer:
Selina Concise Biology Class 7 ICSE Solutions - Excretion in Humans 1

Section through the kidney to show different regions The kidneys is composed of:

  1.  an outer darker area called Cortex
  2.  an inner lighter area called Medulla.

The microscopic structure of kidney is formed of millions of tubules called renal tubules or nephrons.

Question 5.
What are the two ways by which a person can get relief in case of kidney failure ?
Answer:
The two ways by which a person can get relief in case of kidney failure are:

  1. Dialysis: this is a method in which an artificial machine cleans and filters the blood.
  2.  The patient can undergo kidney transplant.

Question 6.
Draw a diagram of human excretory system and label the following parts : Kidney, ureter, urinary bladder and urethra.
Answer:
Selina Concise Biology Class 7 ICSE Solutions - Excretion in Humans 2

Question 7.
How are kidney stones formed ?
Answer:
Kidney stones are formed when crystal forming substances such as calcium oxalate, calcium phosphate and uric acid are
more than the fluid in the urine. When these chemicals start sticking together, they from crystals, commonly called kidney stones. They may be formed and cause severe plain.

Question 8.
 What are the symptoms of an urinary tract infection ?
Answer:
 Common symptoms include a strong and frequent urge to urinate, and a painful and burning sensation while urinating.

 

Selina Concise Biology Class 6 ICSE Solutions – Cell – The Structure and Functions

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Selina Concise Biology Class 6 ICSE Solutions – Cell – The Structure and Functions

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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.

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Selina Concise ICSE Solutions for Class 6 Biology Chapter 3 Cell – The Structure and Functions

Synopsis

  • The single-celled organisms are called unicellular and if the organisms are made up of more than one cell are called multicellular.
  • The simple microscope was developed by Antony Von Leeuwenhoek.
  • The compound microscope was developed by Robert Hooke.
  • The branch of biology which deals with the study of cells is called cytology.
  • The living substance of the cell is called protoplasm.
  • Examples of
    (a) unicellular organisms:

    1. bacteria
    2. amoeba
    3. yeast
    4. chlamydomonas etc.
  • (b) multicelluar organisms: plants like rose, neem, animals like man, hydra etc.
  • Examples of different cellular shapes.
    1. irregular — amoeba
    2. oval — chlamydomonas (slipper organism)
    3. oblong — paramecium
    4. elongated — striated muscle cells
    5. very long or thread like — nerve fibre cells
    6. cubical or rectangular — plant cell
  • The smallest cell — Bacterial cell
    The longest cell — Nerve cells
    The largest cell — Ostrich egg
  • Cell theory explains
    1. Every living organism is made up of one or many cells.
    2. The structural unit of all the living organisms is the cell.
    3. The functional unit of all the living organisms is the cell.
    4. All cells arise from the pre-existing cells.
  • The three scientists who contributed in the cell theory are:

    1. M.J. Schleiden
    2. Theodor Schwann
    3. Rudolph Virchow
  • Animal cells have no cell walls.
  • The cell wall is made up of cellulose which is rigid and gives shape to the cell.
  • The cell wall is freely permeable while the cell membrane is semi-permeable.
  • The supportive framework which helps in the distribution of various product across the cell is endoplasmic reticulum.
  • Power house of the cell — Mitochondria
  • Synthesise proteins — Ribosomes.
  • The organelle found only in the animal cell which initiate and regulate cell division is Centrosome.
  • The organelle found only in the plant cell is plastid.
    Green plastids are chloroplasts
    Other plastids are amyloplasts.
  • Cell organelles are concerned with specific functions.
  • The importance of cell division is.
    1. Production of new cells.
    2. For growth and repair.
    3. Replacement of the dead and worn out cells. –
    4. For reproduction.
  • The process of fusion of sperm and an egg is called fertilisation.
  • The result of fertilisation is Zygote.

Review Questions

Multiple Choice Questions:

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

(i) Identify the part which contain pigment:
(a) cell membrane
(b) plastid
(c) centrosome
(d) cell wall

(ii) The organelle that controls all activities in
(a) nucleus
(b) vacoule
(c) plastids
(d) cytoplasm

(iii) A cell that is spherical in shape is:
(a) white blood cell
(b) nerve cell
(c) red blood cell
(d) amoeba

(iv)The vacuole contains:
(a) water
(b) cell sap
(c) salts
(d) food

Short Answer Questions:

Question 1.
 Name the scientist who invented the first microscope.
Answer :
Antony Von Leeuwenhoek.

Question 2.
Who coined the term “cell” ?
Answer :
The term “cell” was coined by Robert Hooke.

Question 3.
Briefly describe the three essential basic parts of a cell.
Answer :
The essential basic parts of a cell are:

  1. Cell membrane
  2. Cytoplasm
  3. Nucleus
    1. Cell membrane — It is a very thin, delicate and flexible membrane which surrounds each cell. It is also called plasma membrane. It consists of fine pores which allow only certain molecules to pass through it and prohibit the others and therefore, due to its function, also called selectively permeable membrane.
    2. Cytoplasm: This is the living portion of the cell which is a semi-liquid, translucent and colourless liquid. It is the portion of the cell where major functions of the cell are carried out through various finer parts of the cell. The finer structures which are contained in this are called the cell organelles.
    3. Nucleus: The small spherical dark coloured body usually located in the centre of the cell. It is the most important part of the cell which regulates and co-ordinates various life processes. Its major role is during cell division. It contains hereditary factors called the genes.

Question 4.
The cell membrane is called selectively permeable. Why?
Answer :
The cell membrane of the cell is composed of fine pores through which only certain molecules of the different substances can pass into the cell. Since it allows only specific molecules to enter prohibiting the other it is referred to as Selectively Permeable.

Question 5.
State the difference between
Answer :
(i) Nucleus and nucleolus
Nucleus

  1. It is a cell organelle.
  2. It is the most important part of the cell.
  3. It is present in the cytoplasm of the cell.
  4. It is bounded by a delicate nuclear membrane

Nucleolus

  1. It is a component of the nucleus.
  2. It is the most important part of the nucleus.
  3. It is present in the nucleoplasm.
  4. It does not have any such membrane around it

(ii) Cytoplasm and protoplasm
Answer :
Cytoplasm

  1. The living portion of the cell inside the cell except the nucleus.
  2. It has many finer parts contained in it like golgi bodies, mitochondria etc.

Protoplasm
The living substance of a cell is called the protoplast.
It consists of two main parts

  1. cytolasm
  2. nucleus.

(iii) Cell wall and cell membrane.
Answer :
Cell wall

  1. It is made up of cellulose.
  2. It gives shape and rigidity to the plant cell.
  3. It is a non-living structure.
  4. It protects the cell from the entry of disease-causing agents, as well the underlying protoplasm against mechanical injuries.

Cell Membrane

  1. It is very thin, delicate and flexible.
  2. This allows the entry of certain molecules only, while holding back the others.
  3. It is living structure.
  4. It has fine pores in it, through which only certain substances carfpass in and out, while others cannot.

Question 6.
 List the major differences between a plant cell and an animal cell.
Answer :
Plant cell

  1. Cell is comparatively larger with distinct outlines.
  2. Has a definite and rigid cell wall.
  3. Has negligible amount of cytoplasm.
  4. Cytoplasm is not very dense.
  5. Contains plastids.
  6. No centrosome.
  7. Have prominent one or more vacuoles.
  8. Has simple golgi apparatus composed of units called dictyosomes.

Animal cell

  1. Size is small with less distinct outlines.
  2. Cell wall absent.
  3. Cytoplasm fills almost the entire cell.
  4. Cytoplasm is granular and relatively dense.
  5. Do not contain plastids
  6. Centrosomes are present.
  7. Have temporary vacuoles which are small and concerned with secretion or excretion.
  8. Have complex and prominent golgi apparatus.

Question 7.
Briefly discuss the importance of chromosomes to an organism.
Answer :
The most important feature of a living cell is that it can divide or reproduce of its own kind and this function is regulated by the nucleus of the cell. The nucleus in its nucleoplasm contain a network of dark stained thread like structures called chromatin fibres. These fibres during cell division become thick and ribbon like which are then called chromosomes. The chromosomes are the actual hereditary factors. These are unique for each species both in number and in character.
Human body has 46 chromosomes which occur in pairs.
They are further categorised as:

  1. Chromosomes specific for determining the sex of the species called the sex chromosomes.
  2. Other chromosomes are called autosomes.

8. Fill up the blanks with the terms given below in the box.
Pigments, wall, pre-existing, cell, vacoules

  1. The cell is the structural unit of all living things.
  2. All cells arise from pre-existing cells.
  3. Animal cells have no cell wall.
  4. Plastids contain pigments.
  5. Vacoules are filled with water and dissolved substance

Question 9.
Try to find the names of four cell organells hidden in this maze, (hint: The hidden words can appear horizontally or vertically; forwards or backward or even mixed up). Write them in the lines provided. For example :
“NUCLEUS” in the last row, seven backward letters.
Selina Concise Biology Class 6 ICSE Solutions - Cell - The Structure and Functions 1
Answer :
Selina Concise Biology Class 6 ICSE Solutions - Cell - The Structure and Functions 2

  1. Vacuole
  2. Leucoplast
  3. Chromoplast
  4. Nucleus, Plastid

Selina Concise Biology Class 6 ICSE Solutions – Respiratory System

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Selina Concise Biology Class 6 ICSE Solutions – Respiratory System

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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.

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Selina Concise ICSE Solutions for Class 6 Biology Chapter 5 Respiratory System

Synopsis —

  • The energy released during respiration is stored as chemical energy in the form of ATP — adenosine tri-phosphate.
  • Aerobic respiration —
    C6H12O6 + 6O2   →  6CO2 + 6H2O + 38 ATP
    Anaerobic respiration —
    Selina Concise Biology Class 6 ICSE Solutions - Respiratory System 1
  • During vigorous exercise, the cells respire anaerobically and form lactic acid which accumulate in the muscle cells causing fatigue and pain.
  • The respiration in humans occur in three phases:

    1. Breathing
    2. Gaseous Transport
    3. Cellular respiration
  • The oxygen inhaled in combines with haemoglobin present in the red blood cells forming an unstable compound called oxyhaemoglobin.
  • The nasal chamber has got hairy lining to prevent dust particles from reaching the lungs. The lining also has mucous to trap germs and dust.
  • The common passage for the food and air is the pharynx.
  • Trachea is also called the wind pipe.
  • The voice box or the Adam’s apple is the larynx which contains ligamentous folds called vocal cords.
  • Incomplete closure of epiglottis during swallowing causes coughing.
  • The trachea is formed of incomplete C-shaped cartilaginous rings which keep them permanently distended.
  • The lungs are protected outside by the two membranes called outer and inner pleura.
  • Left lung is slightly smaller than the right lung.
  • Left lung has two lobes while the right lung has three lobes.
    Selina Concise Biology Class 6 ICSE Solutions - Respiratory System 2
  • Breathing is an involuntary act.
  • Even after maximum forced expiration, some air is left in the lungs called residual volume.
  • In normal adults, the breathing rate is 12-18/minute while a newborn breathes at about 60 breaths per minute.
  • Asphyxiation is a condition in which blood becomes venous by the accumulation of excess carbon dioxide and the oxygen supply is diminished.
  • The gas composition in artifical respiration is 95% oxygen, 5% carbon-di-oxide.
  • Snoring: Vibration of soft palate during breathing when mouth is kept open while sleeping.
  • Sneezing: It is a protective mechanism through which a foreign irritant particle is thrown out of the lungs suddenly and forcefully.
  • Hiccups: Jerky incomplete inspiration due to blockage of the respiratory tract.

Review Questions

Multiple Choice Questions

1. Put a tick (✓) against the most appropriate alternative in the following statements.

(i) In humans, taken in of the air through nostrils into the nasal cavity is called
(a) Inhalation
(b) Exhalation
(b) Cellular respiration
(d) Internal respiration

(ii) The front opening of the wind pipe is guarded by —
(a) Glottis
(b) Exoglottis
(c) Epiglottis
(d) Trachea

(iii) The process during which food is oxidised and energy is released is called
(a) Cellular respiration
(b) Excretion
(c) Digestion
(d) Transpiration

Short Answer Questions

1. Answer briefly the following:

  1. Why do our body cells require oxygen ?
    Ans. Body cells require oxygen for the break down of glucose and release energy for carrying out various life functions.
  2. What is the difference between breathing and respiration?
    Ans. Breathing is a simple physical process of drawing in air through the nostrils and expelling it out.
    Respiration is a chemical process which involves the breakdown of food and release energy.
  3. Name the by-product formed during the oxidation of food.
    Ans. The by- products formed are
    1. carbon-di-oxide
    2. water
  4. Name the agency which transports oxygen to all parts of the body.
    Ans. Blood .
  5. What is the role of epiglottis during swallowing ?
    Ans. Epiglottis closes the wind pipe at the time of swallowing.

Question 2.
Describe in brief the function of ribs and diaphragm in breathing.
Answer:

  1. Ribs muscles—During inhalation, the ribs muscles contract and push the ribs upward and outward.
    During exhalation these relax and cause the ribs to return to original position.
  2. Diaphragm: During inhalation it becomes flattened while during exhalation it relaxes and moves up and back into convex (dome) shape.

Question 3.
Name the gas which is expelled out during expiration. Where is it originally produced in our body ?
Answer:
The gas which is expelled during expiration is carbon-di¬oxide. It is produced as a result of oxidation of glucose in the tissues. (Cellular respiration)

Question 4.
Name the following:

  1. Respiratory process
  2. in which oxygen is not utilized.
    Ans. Cellular respiration
  3. Respiratory process in which oxygen is utilized.
    Ans. Gaseous transport
  4. The microscopic air-sacs of the lungs.
    Ans. Alveoli
  5. The two membranes which protect the lungs.
    Ans. Outer pleura, inner pleura

Long Answer Questions:
Question 1.
Why is a respiratory system necessary ?
Answer:
Respiratory system is very important for the body. Respiration in human beings is divided into two distinct parts. The first part involves taking in oxygen from the air or what we commonly call breathing. The respiratory system is responsible for breathing in and out of air, and exchange of gases. The main parts of the respiratory system consist of the nostrils, trachea or wind pipe and lungs.
The blood, then, transports the oxygen to the individual cell where it is used for the chemical process of respiration. This is known as cellular respiration.The second part involves taking out carbon dioxide, which is a waste product of cellular function.

Question 2.
What factors are most likely to affect the breathing rate ?
Answer:
Breathing is a necessary function for human beings. It supplies oxygen for a process called cellular respiration, which is how cells manufacture the energy they need for their life functions.
There are lots of things that can affect the rate of breathing in humans and they are:

  1. Exercise is one of those things, particularly aerobic exercise. Aerobic exercise is any exercise that causes the person to breathe more, such as running jogging, playing basketball, football, running track, or playing soccer.
  2. Even Breathing rate also changes while the person is sleeping, sitting at rest or even after climbing the stairs.
  3. Another factor that can influence breathing rate is allergic reactions to stimuli from the environment, such as pollen. This can inflame the passageways leading to the lungs, making them smaller, requiring more air.
  4. Smoking is a habit that can influence the development of lung cancer, which in turn influences the rate a person breathes.
  5. Nervous conditions and reactions to stimuli also influence the breathing rate, such as the fumed “fight or flight” syndrome.

Question 3.
What happens to the energy liberated during respiration?
Answer:
The energy liberated during respiration is utilised for carrying out various life processes.
Some of the energy liberated during the breakdown of the glucose molecule, is in the form of heat, but a large part of it is converted into chemical energy called Adenosine Triphosphate (ATP). Any activity inside the cell is carried out by the energy released by these ATP molecules.

Question 4.
What do you understand by inhalation and exhalation ? How are they different from each other ?
Answer:
The physical process, by which the air containing oxygen is drawn into the lungs and air containing carbon dioxide is forced out from lungs is called breathing. Breathing involves two steps, inhalation (inspiration) and exhalation (expiration).

Inhalation (Inspiration)

  1. Ribs move upwardsand outwards.
  2. Diaphragm is pushed downwards and flattens.
  3. Volume of chest cavity increases.
  4. Lungs expand, air pressure becomes low.
  5. Atmospheric air at higher pressure rushes into the lungs

Exhalation (Expiration)

  1. Ribs move downwards and inward.
  2. Diaphragm moves upwards and becomes dome shaped.
  3. Volume of chest cavity decreases.
  4. Lung size reduces, air pressure becomes high.
  5. Air rushes out of lungs as atmospheric air pressure is lower.

Question 5.
What do you understand by the term respiratory diseases ? Name any three common respiratory diseases.
Answer:
Any of the diseases and disorders that affect human respiration are called Respiratory diseases. Diseases of the respiratory system may affect any of the structures and organs that have to do with breathing, including the nasal cavities, the pharynx (or throat), the larynx, the trachea (or windpipe), the bronchi and bronchioles, the tissues of the lungs, and the respiratory muscles of the chest cage.

  1. Bronchitis — It is a respiratory infection in which the lining of the bronchi becomes inflamed. As this irritated membrane begins to swell, it narrows or shuts off the bronchial passages, resulting in breathlessness and coughing spells.
  2. Asthma — It is a chronic disease that also causes inflammation and swelling in the airways. But this happens periodically. During an asthmatic attack, a patient experiences tightness in the chest, shortness of breath and wheezing. This condition improves considerably with medication.
  3. Pneumonia — It is a respiratory infection caused by a bacteria. This bacteria enters the air sacs, multiplies there and the air sacs may get filled with fluid. This disease causes chest pain, chills and high fever.

Question 6.
State the cause and treatment for the following diseases

  1. Tuberculosis
  2. Pneumonia
  3. Bronchitis

Answer:

  1. Tuberculosis — Cause: Caused by bacteria that can spread by air, dust or sputum.
    Treatment: BCG vaccine, antibiotic — Streptomycin.
  2. Pneumonia — Cause: Mainly caused by bacteria inhaled through air or by contact.
    Treatment: Antibiotics—Penicillin.
  3. Bronchitis — Cause: This respiratory infection is mainly caused by a virus. Air pollution and smoking can also cause bronchitis.
    Treatment: Drinking plenty of fluids, following a well balanced diet, frequent hand washing and adequate rest can prevent and improve bronchitis.

Selina Concise Physics Class 6 ICSE Solutions – Force

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Selina Concise Physics Class 6 ICSE Solutions – Force

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 6 Physics. You can download the Selina Concise Physics ICSE Solutions for Class 6 with Free PDF download option. Selina Publishers Concise Physics 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 Physics Chapter 3 Force

  • Synposis
  • A body not changing position with time with respect to a nearby fixed object is said to be at rest.
  • A body changing position with time with respect to a nearby fixed object is said to be in motion.
  •  Force is a push or pull which can change the state of rest or motion of the body or can change the size and shape of the body (i.e. it can deform a body).
  • A force applied on a body can
    (a) move it, if it is not in motion
    (b) stop it, if it is moving
    (c) increase or decrease its speed
    (d) change its direction of motion
    (e) change its shape or size if it is not free to move.
  • Force is defined as that cause which changes the state of rest or the state of motion of a body and can also deform it.
  • A force has both the magnitude and the direction.
  • When two forces act in opposite directions, the net force is equal to the difference of these forces, in the direction of the bigger force.
  • When two forces act on a body which are equal in magnitude but opposite in direction, the net force on the body is zero.
  • Forces are of two types :
    1. contact forces and
    2. non-contact forces (or forces at a distance).
  • Contact forces are
    1. the muscular force applied as push or pull,
    2. force of friction
    3. the force of reaction normal to the surface and
    4. the force of tension in a string pulled by a load.
  • Non-contact forces are
    1. gravitational force
    2. electrostatic force and
    3. magnetic force
  • The weight of a body is the force with which the earth pulls the body.
  • The unit of weight (or force) is kgf not kg which is unit of mass.
  • Friction is a force that opposes the motion.
  • Friction always acts in a direction opposite to the direction of motion.
  • The cause of friction is the interlocking of the irregular projections on the two surfaces in contact. ‘
  • The force of friction depends on:
    (a) the smoothness (or roughness) of the surfaces in contact, and
    (b) the weight of the sliding (or rolling) body.
  • The force of friction does not depend on the area of the surfaces in contact.
  • The disadvantages of friction are :
    (a) Friction opposes the motion
    (b) Friction produces heat
    (c) Friction causes wear and tear
    (d) Friction reduces efficiency
  • Friction can be reduced by
    (a) making the surfaces smooth
    (b) the use of lubricants
    (c) the use of ball bearings
    (d) streamlining the shape of the moving body.
  • The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  • The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction.
  • The minimum force required to roll a body on a surface is called the force of rolling friction.
  • Rolling friction is less than the sliding friction and sliding friction is less than the static friction.
  • Friction is advantageous to us in almost all activities of our life.

Test yourself

A. Objective Questions

1. Write true or false for each statement

(a) The frictional force acts in the direction of motion of body
Answer. False

(b) The unit of weight is kilogram
Answer. False

(c) A force can change the direction of motion of a moving body.
Answer. True

(d) A force increases the mass of the body when applied on it.
Answer. False

(e) The force of friction is always disadvantageous.
Answer. False

(f) The sliding friction is more than the rolling friction.
Answer. True

(g) Liquids offer more friction than the gases.
Answer. True

(h) A wet oily road offers more friction than a dry rough road.
Answer. False

2. Fill in the blanks

(a) Force is applied as push or pull.
(b) On squeezing a gum tube, its shape changes.
(c) On pulling a string, its length increases.
(d) A moving football when kicked, its direction of motion changes.
(e) On applying brakes on a moving car, its speed slows down.
(f) We use ball bearings to reduce the friction.
(g) Friction opposes the motion.
(h) Lubricants are used to reduce friction.
(i) Friction causes wear and tear of moving parts of machine.

3. Match the following columns

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 1

Answer.

Selina Concise Physics Class 6 ICSE Solutions Chapter 3 Force 2

4. Select the correct alternative 
(a) A body falls downwards because of

  1. electrical force
  2. gravitational force
  3. mechanical force
  4. magnetic force.

(b) A force does not change

  1. mass
  2. length
  3. shape
  4. state of motion.

(c) A force to be expressed correctly requires

  1. only the magnitude
  2. only the direction
  3. both the magnitude and direction
  4. none of the above.

(d) Friction

  1. promotes motion
  2. opposes motion
  3. acts in the direction of motion
  4. is always a nuisance.

(e) Friction is reduced by

  1. making the surfaces wet
  2. making the surfaces dry
  3. making the surfaces rough
  4. sprinkling sand on the surface.

(f) Friction

  1. causes wear and tear
  2. produces heat
  3. stops a moving body
  4. has all the above disadvantages

(g) Friction is increased if

  1. an oil is sprayed
  2. the surfaces are made wet
  3. the surfaces are made dry
  4. the surfaces are polished

B. Short/Long Answer Questions

Question 1.
Name the term used for the push or pull ?
Answer:
Force

Question 2.
Give one example each of a force as

  1. a push
  2. as pull
  3. a stretch and
  4. a squeeze.

Answer:

  1. a push — To1 open a door, we push it.
  2. as pull — To move a grass roller on a lawn, it is pulled by a gardener.
  3. a stretch — Stretching a rubber string.
  4. a squeeze —Change in shape of a sponge on squeezing.

Question 3.
Explain the meaning of the term force.
Answer:
Force: Force is a physical cause that changes or may tend to change the state of rest or the state of motion of an object. The S.I. unit of force is Newton.

Question 4.
What effect can a force have on a stationary body ?
Answer:
When a force is applied on a stationary body, it begins to move.

Question 5.
What effects can a force have on a moving body ?
Answer:
When a force is applied on a moving body, it can be made to stop or it can change the direction of motion.

Question 6.
What effect can a force produce on a body which is not allowed to move ?
Answer:
When a force is applied on a body which is not free to move, it gets deformed i. e., the shape or size of the body changes.

Question 7.
Give one example each to indicate that the application of a force

  1. produces motion
  2. stops motion
  3. slows down motion
  4. changes the direction of motion
  5. deforms a body

Answer:

  1. A car originally at rest when pushed, begins to move.
  2. A moving bicycle is stopped by applying the brakes.
  3. The speed of a moving vehicle is slowed down by applying the brakes.
  4. A player kicks a moving football to change its direction of motion.
  5. On stretching a rubber string, its length increases.

Question 8.
State the effect produced by a force in the following cases :
(a) The sling of a rubber catapult is stretched
(b) A man pushes a heavy cart
(c) A player uses his stick to deflect the ball .
(d) A cyclist applies brakes
(e) A spring is compressed.
Answer:
(a) The shape and size of catapult changes i.e., its length increases.
(b) The heavy cart begins to move.
(c) The direction of the ball changes.
(d) The speed of the moving cycle is slowed down.
(e) There is change in size and shape of spring.

Question 9.
Name the two kinds of forces in nature.
Answer:
Two kinds of forces in nature are :

  1. Contact forces
  2. Non contact forces

Question 10.
Name the type of force which acts in the following cases:
Answer:
(a) A coolie lifts a luggage
Answer. Muscular force
(b) A bicycle comes to rest slowly when the cyclist stops pedalling
Answer. Frictional force
(c) A stone falls from a roof
Answer. Gravitational force.
(d) A comb rubbed with silk attracts the bits of paper
Answer. Electrostatic force
(e) A string hangs with a load
Answer. Force of tension.
(f) A horse moves a cart
Answer. Muscular force
(g) A magnet attracts an iron pin
Answer. Magnetic force
(h) A boy opens the door
Answer. Muscular force
(i) An apple falls from a tree
Answer.Gravitational force
(j) A man rows a boat.
Answer. Muscular force.

Question 11.
What do you mean by the gravitational force ? Give an example to illustrate it.
Answer:
The force of attraction on a body by earth is called gravitational force.
Example : The leaves and fruits fall from a tree downwards towards the ground, water in a river flows down streams, a ball thrown up goes to a height and then returns back on ground are some examples of motion due to gravitational force.

Question 12.
Define the term “weight of a body”
Answer:
Weight: The weight of the body is the force with which the earth attracts it towards the centre. It depends on acceleration due to gravity.

Question 13.
What do you understand by the term friction ?
Answer:
Friction: Friction is that force which opposes the relative motion between the two surfaces that are in contact with each other.

Question 14.
Give an example to illustrate the existence of force of friction.
Answer:
If we stop paddling our bicycle, it gradually slows down and ultimately it stops after travelling a certain distance. This is due to frictional force between bicycle and ground.

Question 15.
What is the cause of friction ?
Answer:
The cause of friction is the interlocking of the irregular projections on the two surfaces in contact.

Question 16.
State two factors which directly affect the force of friction.
Answer:
Two factors which directly affect the force of friction are :

  1. The smoothness of the surface.
  2. The presence of solid, liquid or gas around the moving body.

Question 17.
In which case will there be more friction between the truck and the road : when the truck is empty or when it is loaded ?
Answer:
When the truck is loaded there will be more friction between the truck and the road.

Question 18.
Which offers more friction on a body : a glass surface or a wooden surface ?
Answer:
Wooden surface offers move friction on a body.

Question 19.
Name the three kinds of friction.
Answer:
Friction is of three kinds :

  1. Static friction
  2. Sliding friction,
  3. Rolling friction

Question 20.
List three disadvantages of friction.
Answer:
Disadvantages of friction:

  1. Friction produces heat which damages the moving parts of a machine.
  2. Friction produces wear and tear on the contacting surfaces. This reduces the life of machine parts, tyres and shoe soles.
  3. A lot of energy is wasted due to friction to overcome it before moving.

Question 21.
When you apply the brakes, the bicycle stops and the rim of the wheel becomes hot. Explain the reason.
Answer:
It is due to friction between the brakes and the rim of the wheel that it becomes hot.

Question 22.
The eraser gets smaller and smaller as you use it more and more. Explain the reason.
Answer:
The eraser gets smaller and smaller as we use it more and more due to frictional force causing wear and tear of the eraser.

Question 23.
List three ways of reducing friction.
Answer:
Ways to reduce friction:

  1. Providing ball bearings or wheels between the moving parts of machine or vehicles reduce friction and allow smooth movement as rolling friction is less than sliding friction.
  2. Oiling or lubricating (with graphite or grease) the moving parts of a machine reduces friction. Fine powder like talcum powder also works as a lubricant to reduce friction.
  3. Polishing the rough surface reduces friction offered by it.
  4. Streamlining (giving special shape to experience minimum drag) the bodies of aeroplanes, cars, boats and ships help reduce drag (fluid friction) while travelling through air or water.

Question 24.
It is difficult to open an inkpot with greasy or oily hands. Explain.
Answer:
When the hands are oily, then the oil acts as lubricant and reduces the friction.
As the friction force is less, it is difficult to get grip of the inkpot and it becomes difficult to open it.

Question 25.
It is difficult to walk on a wet road. Explain.
Answer:
When the road becomes wet after rain, friction is reduced and hence, the road becomes slippery.

Question 26.
Give three examples to illustrate that friction is a necessary evil.
Answer:
The examples to illustrate that friction is a necessary evil are:

  1. If friction were absent, we would not be able to walk.
  2. Friction is necessary to burn a matchstick.
  3. It is due to friction that we can write on a board by a chalk.

Question 27.
Define

  1. static friction
  2. sliding friction and
  3. rolling friction

Answer:

  1. The maximum force exerted by a surface on a body so long as it remains stationary is called the force of static friction.
  2. The minimum force required to keep the body moving over a surface such that it moves equal distances in equal intervals of time is called the force of sliding friction..
  3. The minimum force required to roll a body on a surface is called the force of rolling friction.

Question 28.
Arrange the following in descending order :

  1. static friction
  2. sliding friction and
  3. rolling friction?

Answer:
Static friction > Sliding friction > Rolling friction.

Question 29.
A body needs a force F1 just to start motion on a surface, a force F2 to continue its motion and a force F3 to roll on the surface. What is

  1. the static friction
  2. sliding friction and
  3. rolling friction ? State whether F2 is equal, less than or greater than (1) F1 and (2) F3.

Answer:

  1. F1 = Static friction
  2. F2 = Sliding friction
  3. F3 = Rolling friction
    F1 > F2 > F3
    F2 is less than F1 but greater than F3.

Selina Concise Physics Class 6 ICSE Solutions – Light

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Selina Concise Physics Class 6 ICSE Solutions – Light

ICSE SolutionsSelina ICSE SolutionsML Aggarwal Solutions

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Selina Concise ICSE Solutions for Class 6 Physics Chapter 5 Light

  • Synposis
  • Light itself is not visible, but in the presence of light other objects become visible A.
  • Light is defined as the external physical cause that affects the eye to produce the sensation of vision.
  • Two types of sources of light are:
    (1) Natural sources such as sun, stars andjugnu.
    (2) Artificial sources such as fire, electric lamp, electric tube light, a burning candle, a kerosene lamps heated bodies, etc.
  • The bodies which themselves emit light are called luminous bodies. Examples: torch, electric lamps electric tube light, burning candle, kerosene lamp, sun, stars. Jugnu etc.
  • The bodies which do not emit light by their own, but they become visible because of the light falling on them from a luminous body, are called non-luminous bodies. Examples: moon, earth, table, book, chair etc.
  • A medium which allows the passage of light through it easily, is called a transparent medium. Examples: glass, air, water etc.
  • A medium which allows only a small amount oflight to pass through it, is called a translucent medium. Examples: ground glass, tracing paper etc.
  • A medium which does not allow anydight to pass tough it, is called an opaque medium. Examples: wood, metals etc.
  • Light travels in a straight line path. This is called the rectilinear propagation oflight.
  • The pin hole camera is a simple application of the rectilinear propa – gation oflight.
  • The image (or picture) formed in a pin hole camera is upside down (i.e. inverted). On increasing the distance of screen from the pin hole, the size of image increases.
  • The shadow of an opaque object is the dark patch obtained on the screen when that opaque object is placed in the path of light.
  • Shadow is formed because light travels in a straight line path.
  • The shadow is similar to the shape of the object.
  • The part of the shadow where no light reaches from the source is completely dark and is called the umbra.
  • The part of the shadow where light reaches from only a portion of the source is partially dark and is called the penumbra.
  • There is only umbra in the shadow of an opaque object due to a point source. The umbra is bigger in size than that of the obj ect. The umbra increases in size if the screen is moved away from the object.
  • The shadow of an object due to a light source smaller than the object contains an umbra surrounded by a penumbra. The umbra is bigger in size than that of the object. Both the umbra and penum¬bra increase in size as the screen is moved away from the source.
  • The shadow of an opaque object due to a light source bigger than the object contains an umbra (which is much smaller in size than the object) surrounded by a penumbra. The umbra diminishes while the penumbra increases in size if the screen is moved away from the object.
  • Lunar and solar eclipses are the examples of formation of shadows in nature.
  • A lunar eclipse is caused on a certain full moon night when the earth comes in between the sun and the moon so that the earth casts its shadow on the moon.
  • A solar eclipse is caused on a certain new moon’s day when the moon comes in between the sun and the earth so that the moon casts its shadow

Test yourself

A. Short Answer Questions

1. Write true or false for each statement

(a) The moon is a natural source of light.
Answer. False

(b) The moon is self luminous.
Answer. False

(c) We can see an object through an opaque medium.
Answer. False

(d) Light passes through glass.
Answer. True

(e) Light travels in a straight line path. .
Answer. True

(f) Image formed in a pin hole camera is real.
Answer. True

(g) The image in a pin hole camera gets blurred if the hole is made bigger.
Answer. True

(h) A shadow is formed because light travels in a straight line path.
Answer. True

(i) Solar eclipse occurs when the sun comes in between the earth and the moon.
Answer. False

(j) If the shadow of earth falls on the moon, the eclipse is called the lunar eclipse.
Answer. True

2. Fill in the blanks

(a) Light gives us the sensation of vision.
(b) The sun is a natural source of light.
(c) A medium through which light cannot pass is called the opaque medium.
(d) A medium which allows light to pass through it easily is called the transparent medium.
(e) Moon is a non-luminous body.
(f) Light travels in a straight line path.
(g) In a pin hole camera, the image formed is inverted and real.
(h) The darkest portion of a shadow is called the umbra.
(i) The less dark portion of a shadow is called the penumbra.
(j) Lunar eclipse occurs when the earth comes in between the moon and the sun.

3. Match the following columns
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 1
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 2

4. Select the correct alternative

(i) The natural source of light is

  1. candle flame
  2. electric lamp
  3. sun
  4. kerosene lamp

(ii) The formation of inverted image in a pin hole camera shows that

  1. light enables us to see
  2. light travels in a straight line path
  3. light can pass through the pin hole
  4. light does not pass through the pin hole

(iii) The luminous body is

  1. a lighted bulb
  2. earth
  3. noon
  4. table

(iv) Umbra is a region of

  1. complete darkness
  2. partial darkness
  3. complete brightness
  4. partial brightness

(v) Penumbra is a region of

  1. complete darkness
  2. complete brightness
  3. partial brightness
  4. none of the above

(vi) Solar eclipse occurs on

  1. every new moon’s day
  2. certain new moon’s day
  3. every full moon’s day
  4. certain full moon’s day

(vii) Lunar eclipse occurs on

  1. every full moon’s night
  2. certain full moon’s night
  3. every new moon’s day
  4. certain new moon’s day

B. Short/Long Answer Questions

Question 1.
What is light ? Define it.
Answer:
Light is a form of Energy i. e. The external physical cause that affects our eye to produce the sensation of vision.

Question 2.
How does light make an object visible ?
Answer:
An object becomes visible to us when the light after striking the object reaches our eyes. Light itself is not visible, but light makes objects visible to us.

Question 3.
Name two natural sources of light.
Answer:
Sun, stars,jugnu, firefly.

Question 4.
List two artificial sources of light.
Answer:
Electric bulb, torch, an oil lamp, fluorescent tube, candle.

Question 5.
Differentiate between the luminous and non-luminous bodies. Give two examples of each.
Answer:
Difference Between
Luminous
The bodies which have light of their own e.g. sun stars, bulb, candle, oil lamp, torch, a lantern.
Non-Luminous
The bodies-which do not have their own Iight.e.g. moon, chair, table. When light falls on them, they become visible.

Question 6.
Is the moon a luminous object ?
Answer:
Moon is not a luminous body, it is nbn-luminous body. It has no light of its own.

Question 7.
What do we call a body that shmes on its own ?
Answer:
The bodies that shines onits ownor whichthemselves emittheir own light are called the luminous bodies.

Question 8.
What do we call an electric bulb producing light ?
Answer:
Luminous object.

Question 9.
What is a transparent medium ? Give two examples.
Answer:
Amedium which allows the passage of light through it easily,is called a transparent medium.
Examples: glass, air, water etc.

Question 10.
Explain the difference between a transparent, a translucent and an opaque medium. Give two examples of each.
Answer:

  1. Transparent objects — Those objects through which light can pass easily are called transparent obj ects. e.g. Water, glass, air.
  2. Translucent object— The ohj ect through which light can pass partially are called translucent object, e.g. tracing paper, waxed paper.
  3. Opaque object— The objects which do not allow the light to pass through are called opaque objects, e.g. wood.

Question 11.
What do we call a substance through which we cannot see light ? Give an example of such a substance.
Answer:
A substance through which we cannot see light is called an opaque medium.
Examples:  Wood, metals, butter paper and black paper etc.

Question 12.
What do we call a substance through which light passes ? Give an example of such a substance.
Answer:
A substance through which light passes is called a transparent substance.
Examples: glass, air, water etc.

Question 13.
Can a transparent medium form an image ? Explain your answer.
Answer:
No, a transparent medium cannot form image. All the light that passes through a transparent medium completely pass through the substance. For the formation of image it is must that the light rays get reflected through the surface.

Question 14.
How can you obtain a point source of light ?
Answer:
A point source of light is obtained either by placing a screen having a fine hole, in front of die luminous body or by placing the luminous body inside a box having a fine hole on one of its side.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 3

Question 15.
Define the terms : a ray of light and a beam of light.
Answer:
The light travelling in any one direction in a straight line is called a ray of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 4
A group of light rays given out from a source is called a beam of light
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 5

Question 16.
What do you mean by ‘rectilinear propagation of light’ ?
Answer:
Light travels in a straight line path. This is called the rectilinear propagation of light.

Question 17.
Describe an experiment to show that light travels in a straight line path.
Answer:
Take three cardboards A, B and C each about 25 cm square. Take a pin and make a small hole in each cardboard at the same height. Suspend the cardboard pieces by separate threads vertically from a support such that each hole is at the same height, as shown. Pass a string through the holes and pull it taut. This makes the three holes in a straight line. Now take out the string.
Place a lighted candle near one of the cardboards (say A). Look at the candle flame from the other side of the cardboard C. The candle flame is clearly seen.
Now slightly displace one of the cardboards (say B) so that the holes no longer remain in a straight line. Again look at the candle flame from the other side of the cardboard C. You do not see the candle flame. The reason is that light travels in a straight line and now the holes in the cardboards A, B and C are not in a straight line.
Conclusion: Light travels in a straight line path called the rectilinear propagation of light.

Question 18.
In which of the following two arrangements (a) and (b) shown in the diagram, you can see the light of the bulb ? Explain Your answer
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 6
Answer:
We can see the light of the bulb in the arrangement (a).
This is so because in arrangement ‘a’ the rod is straight and light travels in a straight line path.
Whereas in arrangement ‘b’ the rod is bent. So the light cannot pass through it.

Question 19.
Name a simple application of the rectilinear propagation of light
Answer:
The simple applications of rectilinear propagation of light are pin hole camera, formation of shadows and elipses.

Question 20.
What is a pin hole camera ? Draw a neat and labelled diagram to show the formation of image of a lighted candle by it.
Answer:
The pin hole camera is a simple application of the rectilinear propagation of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 7

Question 21.
Explain the formation of image of a luminous object in a pin hole camera with the aid of a neat diagram.
Answer:
When a luminous object AB, such as a lighted candle, is placed in front of the pin hole, an inverted picture A’ B’ of the candle is
obtained on the tracing paper. This picture A’ B’ is called the image. The image obtained is upside down (i. e. inverted). The reason is that the light travels in a straight line path. Hence light from the upper point A of the candle passes through the pin hole and strikes
the tracing paper at A’. Similarly, light from the lower point B of the candle passes through the pin hole and strikes the tracing paper
(or screen) at B’. Light from all the other points between A and B, on passing through the pin hole strikes the tracing paper in between
A’ and B’. As a result, an inverted image of the candle is seen on the tracing paper Fig shows the simple ray diagram for die formation of image.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 8

Question 22.
State two factors which affect the size of image formed in a pin hole camera.
Answer:
Factors affecting the size of the image :
The size of image depends on the following two factors:

  1. The distance of screen (i.e. tracing paper) from the pin hole, and
  2. The distance of obj ect (i.e. candle) in front of the pin hole.

Question 23.
Is the image obtained in a pin hole camera erect or inverted ? Give reason for your answer.
Answer:
Image obtained in a pin hole camera is inverted.
The reason is that the light travels in a straight line path. Hence light from the upper point of the candle passes through the pin hole and strikes the tracing paper in the lower point. Similarly light from the lower point of the candle passes through the pin hole and strikes the tracing paper at the upper point.

Question 24.
How is the image affected in a pin hole camera when another fine hole is made near the first pin hole ?
Answer:
If another pin hole is made near the first pin hole, two images are formed on the screen, one due to each of the two pin holes. If the holes are very close, the two images tend to overlap each other. As a result, a blurred image will be seen.

Question 25.
State the effect on the image in a pin hole camera if

  1. The hole is made bigger.
  2. The luminous object is moved towards the pin hole.
  3. The length of the pin hole camera is increased (le. the screen is moved away from the pin hole).

Answer:

  1. If the hole is bigger than a pin hole, again a blurred image in seen. The reason is that a bigger hole is equivalent to a large number of pinholes. Each pin hole produces one image. These images overlap each other resulting in a blurred image.
  2. If the object is moved towards the pin hole the size of the image increases.
    The size of image / The size of object = Distance of screen from pin hole / Distance of object from pin hole
  3. When the length of the pin hole camera is increased. C is the screen is moved away from the pinhole, the size of image also increases.

Question 26.
What is a shadow ? Give a reason for its formation.
Answer:
Shadow : When light falls on an opaque object, light is obstructed and a dark patch on a screen kept behind is called shadow. This is because light propagates in straight line. If distance between obj ect and screen is less, the shad o w will be (umbra) dark and smaller.
If the distance is increased shadow will be dim and larger.

Question 27.
Draw a ray diagram to show the formation of shadow of an opaque object by a point source of light. How is the size of shadow affected if the screen is moved away from the object?
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 9
If we move the screen away from the object, the shadow increases in size.

Question 28.
State two differences between an umbra and a penumbra.
Answer:
Umbra

  1. It is the portion of shadow where no light reaches from the source of light due to the opaque object.
  2. It is completely dark.

Penumbra
It is the portion of shadow where a portion of light from the source of light reaches the shadow even in the presence of the opaque object in between them.
It is not completely dark, but is dim (or less bright).

Question 29.
Draw a ray diagram to show the formation of umbra alone.
Answer:
Formation of umbra alone.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 10

Question 30.
Draw a ray diagram to show the formation of umbra and penumbra both. Label the parts umbra and penumbra in your diagram.
Answer:
If your move the screen away from the object, the shadow increases in size. Formation of umbra and penumbra both.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 11

Question 31.
In each of the following diagrams, draw rays to form umbra and penumbra on the screen.
(a)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 12
(b)

Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 13
Answer:
(a)A’B’—umbra
Umbra alone is obtained on the screen when the opaque object is illuminated by a point source of light.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 14
(b)
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 15
EF is Penumbra CD is umbra.

Question 32.
State the conditions when only the penumbra of an opaque object is obtained on the screen.
Answer:
If the size of source of light is bigger than the size of the opaque object, the size of umbra is very small. If the screen is moved away from the object, the umbra vanishes and only the penumbra remains.

Question 33.
Why is it that the birds flying in the sky do not cast their shadow on the earth ?
Answer:
We do not see the shadow of a bird flying high up in air because in their shadow, the umbra is absent and the penumbra is too large and too faint that it is not visible as the distance of screen (i.e. earth) is very large from the object (i.e. bird).

Question 34.
Why are shadows at noon shorter than in the morning or in the evening ?
Answer:
At noon the sun is directly overhead. So, the sun rays fall vertically on the body. Hence the shadow is very short. In the morning and evenings, the sun rays fall in an inclined position. So, the shadows are long.

Question 35.
What is an eclipse ? Name the two types of eclipses.
Answer:
Eclipses are the examples of formation of shadows in nature. There are two kinds of eclipses:

  1. Lunar eclipse (the eclipse of the moon), and
  2. Solar eclipse (the eclipse of the sun).
    Lunar eclipse is due to the formation of shadow of earth on moon and solar eclipse is due to the formation of shadow of moon on earth.

Question 36.
When does a lunar eclipse take place ? Does it occur on every full moon’s night ?
Answer:
A lunar eclipse occurs when the earth comes in between the sun and moon and casts its shadow on moon. On a full moon night, the moon rises in the east after sun sets in the west. On such a night, the sun and moon are on the opposite sides of the earth. The shadow of the earth falls on the surface of the moon therefore moon is not visible to us. This is lunar eclipse as shown in the figure.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 16

Question 37.
Draw a diagram to show the formation of lunar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 17

Question 38.
When does a solar eclipse take place ? Does it occur on even’ new moon’s day ?
Answer:
Solar eclipse— On a certain moon’s day the moon, happens to come in between the sun and the earth. They come in a straight line. In such a situation, the moon being smaller in size casts its shadow only on a limited region on the earth. In these regions of the earth, the solar eclipse occurs.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 18

Question 39.
Draw a diagram to show the formation of solar eclipse.
Answer:
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 19

Question 40.
What is annular solar eclipse ? Draw a labelled diagram to show its formation.
Answer:
An annular solar eclipse occurs when only the tip of the umbra of the moon falls on the earth. From the point D, the sun will appear to be completely obstructed by the moon, only the outer rim of the sun, called corona, is then visible for a very short time which is known as the diamond ring. The formati on of annular solar eclipse is shown below.
Selina Concise Physics Class 6 ICSE Solutions Chapter 5 Light 20

Selina Concise Biology Class 8 ICSE Solutions – Nervous System

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Selina Concise Biology Class 8 ICSE Solutions – Nervous System

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APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 8 Biology Chapter 7 Nervous 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 7 Nervous System

REVIEW QUESTIONS

Multiple Choice Questions:

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

(a) Medulla oblongata controls

  1. Smelling
  2. Beating of heart and respiratory movement
  3. Intelligence and will power
  4. Balancing the body

(b) Balance of body is controlled by:

  1. Spinal cord
  2. Cerebellum
  3. Cerebrum
  4. Medulla

(c) The smell of good food causes watering of your mouth. It is a

  1. Natural reflex
  2. Acquired relfex
  3. Inborn reflex
  4. Ordinary reflex

(d) The structural and functional unit of nervous system is a

  1. Axon
  2. Nephron
  3. Neuron
  4. Texon

Short Answer Questions:

Question 1.
Name the two types of coordination which take place in our body.
Answer:
(a) Nervous coordination: By nerves and brain
(b) Chemical coordination: By hormones

Question 2.
Your are driving your bicycle at a fast speed. Suddenly, a small boy comes in front of your cycle and, without wasting any time in thinking, you immediately apply the brakes and accident is avoided. What name is given to such an action?
Answer:
Reflex action (acquired).

Question 3.
Given below is the diagram of a neuron. Name the parts numbered 1-5.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 1
Answer:

  1. Dendrite
  2. Nucleus
  3. Cell Body (Nyton)
  4. Axon (Nerve fibre)
  5. Node of Ranvier

Question 4.
Write one word in the space provided to complete the second pair of the related words pertaining to nervous system.
Memory : cerebrum : : breathing :
Balance : cerebellum : : reasoning :
Answer:
Memory : cerebrum : : breathing: medulla oblongata
Balance : cerebellum : : reasoning : cerebrum

Question 5.
Differentiate between the following pair of terms:
(a) Stimulus and impulse
(b) Receptor and effector
(c) Motor nerve and sensory nerve
Answer:
(a) Stimulus: Any change in the environment that usually results in change in the activity of the body.
Impulse: A wave of electrical disturbance that runs through the nerves.

(b) Receptor: The nerve cell on receiving the stimulus sets up the waves of impulses towards the central nervous system.
Effector: Any muscle or gland on receiving the impulse from the brain (or the spinal cord), contracts or secretes.

(c) Motor nerve: It contains only motor neurons,
Example: Nerves going to the muscles of the eyeball.
Sensory nerve: It contains only sensoiy neurons.
Example: optic nerve of the eye.

Question 6.
(a) Name the three major divisions of the human nervous system.
(b) Name the three main parts of human brain.
Answer:
(a)

  1. The central nervous system (brain and spinal cord)
  2. The peripheral nervous system
  3. The autonomic nervous system

(b)

  1. Cerebrum
  2. Cerebellum
  3. Medulla oblongata

Question 7.
Give the function of each of the following:
(a) Olfactory nerve:
(b) Optic nerve:
(c) Facial nerve:
Answer:
(a) Olfactory nerve: The sense of smell is present in the epithelial layers of the nasal chambers. The sense of smell is carried to the brain by the olfactory nerve. They arise from the anterior ends of the olfactory lobes and are distributed to lining of nasal chambers.
(b) Optic nerve: It carries the reflection of the object from the retina to the brain. The image formed on the retina is in a reverted position and the correct picture is formed in the brain as the object is. The optic nerves arise from the side of diencephalon. They innervate the retina of the eye and are sensory in nature.
(c) Facial nerve: It carries message and all expressions of the face, mastication work alone by the teeth, movement of the neck and the activities of the salivary glands to the brain. It arises from the side of medulla. On the whole facial nerves are mixed in nature.

Long answer questions

Question 1.
With the help of a suitable diagram describe the structures of a neuron.
Answer:
Nervous system consists of special cells called nerve cells or neurons. It has a main cell body called cyton. It gives out many processes called dendrites. From it a very long process is given out. It is called axon or nerve fibre.
Selina Concise Biology Class 8 ICSE Solutions – Nervous System 2
The cell body has a nucleus. The dendrites get the message from the organs and send this message to the axon through the cell body. Then the axon sends the message to muscles to contrast or to the gland for secretion.
The neurons make contact with one another through their processes. The axon at its end branches and meets the dendrites of another neuron. The meeting point is called synapse. The message is passed on from one axon to the dendrites of another neuron. How the message goes ? It is like this:
Organ → Message goes to dnedrites → Cell body → Axon → Muscles or glands

Question 2.
Briefly describe the structure of the cerebrum in human brain and mention its functions.
Answer:
Brain consists of main three parts and lies in the cranial cavity of skull.

  1. The cerebrum
  2. The cerebellum
  3. The medulla oblongata

Cerebrum: It is very large and form two third of the whole brain. The two hemispheres are separated from each other by a deep longitudinal groove, the median fissure. The outer surface is folded with ridges and grooves. The hemispheres are hollow from inside and their walls have outer and inner portions. The outer portion has cell bodies of the neurons and it is called grey matter.
The wavery edges of the folded layer has large number of neurons to the extent of nine billion. The inner portion of the cerebrum has axons and it is called white matter.

Functions:

  1. It controls all the voluntary activities.
  2. It is the seat of intelligence, consciousness and will power.

Question 3.
Mention the three functions of spinal cord.
Answer:
Spinal cord has the following functions.

  1. It is the centre of reflex actions below the neck.
  2. It carries messages from the skin and muscles to the brain.
  3. All the stimuli and responses are passed from and to the brain through the spinal cord.

Question 4.
With the help of suitable example, describe reflex action.
Answer:
Reflex action: Reflex actions are automatic responses to stimuli. These actions are not under the control of the animal. They are of definite and mechanical type. Peripheral nervous system and spinal cord both control certain action and the brain is not in action.
Some examples of reflex actions are:

  1. Pupil becomes narrow when strong light falls on it.
  2. The aroma of the food makes the mouth watering.
  3. The hand is withdrawn as we touch the hot plate.
  4. Flow of bile from the gall bladder into the duodenum.
  5. A loud thud may lead to opening of the mouth.

In a reflex action brain is not involved, removing the hand on touching a hot plate is a reflex action. The impulse of heat goes from the hand to the spinal cord and the order is sent back to the muscles of the hand to remove the hand from the hot plate.

Question 5.
Describe three kinds of nerves, giving the example of each.
Answer:
A nerve is formed by a group of nerve fibres (axons) encased by tubular medullary sheath. The medullary sheath acts as insulation and do not allow mixing up of impulses of the neighbouring axons (nerve fibres) We have three kinds of nerves:

Selina Concise Biology Class 8 ICSE Solutions – Nervous System 3

  1. Sensory nerve: It brings impulses from sense organs as these have sensory fibres. These nerve carry the impulses from the sense organs to the brain or to the spinal cord as optic nerve of the eye.
  2. Motor nerves: These carry impulses to muscles or glands from the brain or spinal cord. These nerves have only motor fibres as nerves to the muscles of the eye ball.
  3. Mixed nerve: It has both sensory and motors fibres as nerve going to the tongue.

Question 6.
Differentiate between natural reflex and conditioned reflex. Give examples to illustrate your answer.
Answer:
Natural reflex: It is one in which no previous experience or learning is required. These reflexes are inborn i.e. inherited from the parents.
Examples are

  1. Blinking, coughing, sneezing as these are protective reflexes
  2. Salivation, swallowing, peristalsis as it provides functional efficiency.
  3. Dilation of the eyes pupil to look in the dark and vice versa. It is muscular movement.
  4. Pushing along of swallowed food through the food canal. It is muscular movement.

Conditioned Reflex: It is one which develops during lifetime due to experience or learning.
Examples are:

  1. Watering of mouth (Salvination) at the sight of a tasty food.
  2. Surfing the channels while watching the television.
  3. Typing of a keyboard of a computer.
  4. Playing a musical instrument.