Selina ICSE Solutions for Class 9 Biology

Selina Concise Biology Class 9 ICSE Solutions Nutrition

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Selina Concise Biology Class 9 ICSE Solutions Nutrition

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 10 Nutrition. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina ICSE Solutions for Class 9 Biology Chapter 10 Nutrition

Exercise 1

Solution A.

  1. (c) Fructose and glucose
  2. (d) Potassium – Banana
  3. (b) and (c). (Note: Marasmus is mainly caused due to the deficiency of proteins, but as per the options provided, the right answer would be both carbohydrates and fats.)
  4. (a) A, D and E
  5. (c) Carrot
  6. (a) C

Solution B.1.

(a) T (True)
(b) F (False). Kwashiorkor is a severe protein deficiency disease.
(c) F (False). Iodine is required for the proper working of thyroid.
(d) F (False). Antibodies are proteins produced by the immune system of the body, when it detects harmful substances called antigens.
(e) T (True)

Solution B.2.

(i) Fluorine
(ii) Iodine
(iii) Iron

Solution C.1.

CARBOHYDRATES EXAMPLES USES
(i) Monosaccharides 1.Glucose Provides an instant source of energy
2.Fructose Needed for maintaining a healthy body
(ii) Disaccharides 1.Sucrose Needed for good health
2.Maltose Further broken down to produce glucose molecule which provides energy to the body
(iii) Polysaccharides 1.Cellulose Acts as roughage which prevents constipation
2. Glycogen Reserve carbohydrate in humans and stored in liver and muscles

Solution C.2.

Balanced diet is defined as the one which contains all the principal constituents of food in proper quantity.
Balanced diet is the one that provides at least 50% of energy from carbohydrate, 35% from fat, and 15% from protein. The precise optimal quantities of each nutrient will vary with age, sex and activity.

Solution C.3.

Bones are generally made of calcium and iron. Milk and milk products are rich in calcium and Vitamin A. That is why, a doctor advises a bone patient to include more of milk and milk products in his everyday food to make his bones and teeth strong. Milk also prevents oxidation of Vitamin A. Calcium present in milk even helps in clotting of blood. Milk, is therefore a wholesome food.

Solution D.1.

Need for food by the body:

  1. Growth: Food is necessary for building new protoplasm or cells. This helps in the growth of an organism.
  2. Repair: Food provides materials for the repair of worn out or damaged cells and tissues.
  3. Energy: We obtain energy from food. This energy is required for carrying out various life functions.
  4. Maintenance: Nutrients obtained through food help to maintain the chemical composition of cells.
  5. Provision of raw materials: Raw materials required for the synthesis of products such as enzymes, hormones, sweat, milk, etc. are obtained through food.
  6. Protection: Food provides protection from diseases and infection.

Solution D.2.

Proteins are the body building foods. They provide the chemical material for the growth and repair of body cells and tissues. At the time of emergency, proteins can also be oxidized in the body to release energy.
Protein deficiency disease of young children: Kwashiorkor

Solution D.3.

Whole grain atta, fruits and green leafy vegetables are the chief sources of roughage.

  1. Roughage does not provide any nutrients to our body. It still has nutritive value and is essential for the proper functioning of the gut.
  2. It absorbs a lot of water and retains it. In this way, it keeps faecal matter soft preventing constipation.
  3. It combines with intestinal waste and makes it bulky.
  4. It helps in the formation of stools and helps our body to expel the undigested waste food.
  5. Roughage expands the intestinal lumen and helps in slow and smooth movement of food through the gastrointestinal tract. This movement is required for proper and complete digestion of food and for the elimination of intestinal waste.
  6. Roughage stimulates secretion from the digestive tract and also helps in removal of cholesterol, fatty secretory substances and toxins from the body.

Solution E.1.

VITAMIN RICH SOURCE DEFICIENCY DISEASE
(i) Thiamine Whole grain Beri-beri
Niacin Milk (ii) Pellagra
(iii) Ascorbic acid (iv) Citrus fruit Scurvy
Calciferol (v) Fish liver oil (vi) Rickets
(vii) Retinol Carrot, yellow fruit (viii) Night blindness

Solution E.2.

Mineral Function Rich Source
Iodine Promotes the secretion of thyroxine by the thyroid gland Iodised salt, sea foods
Iron Formation of haemoglobin Whole cereals, fish
Calcium Allows muscle contraction and clotting of blood Dairy foods, beans
Potassium Controls nerve and muscle activity, fluid balance, secretion of neurotransmitter Banana, potato

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Selina Concise Biology Class 9 ICSE Solutions Cell: The Unit Of Life

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Selina Concise Biology Class 9 ICSE Solutions Cell: The Unit Of Life

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 2 Cell: The Unit Of Life. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina ICSE Solutions for Class 9 Biology Chapter 2 Cell: The Unit Of Life

Exercise 1

Solution A.

(a) Ribosomes → Synthesis of proteins
(b) a single cell
(d) cell membrane
(a) absence of centrosome
(c) Cellulose
(a) Mitochondria

Solution B.1.

(a) Mitochondria
(b) Ribosomes
(c) Chromosomes
(d) Centrosome
(e) Lysosomes
(f) Cell membrane

Solution B.2.

(a) F (False). Animal cells do not contain a cell wall.
(b) F (False). A cell wall is made up of cellulose.
(c) T (True)
(d) T (True)
(e) F (False). In eukaryotes, cytoplasm is the part of the cell which surrounds the nucleus.
(f) T (True)
(g) T (True)

Solution B.3.

23 pairs of chromosomes are found in human cells.

Solution B.4.

DNA (Deoxyribonucleic acid)

Solution B.5.

Column A  Column B
    (a) Vacuoles (iii) Covered by tonoplast
    (b) Nucleolus (v) Forms RNA
    (c) Lysosomes (i) Intracellular digestion
    (d) Anthocyanin (iv) Dissolved in the cytoplasm
    (e) Cristae (ii) Respiratory enzymes

Solution B.6.

(a) Lysosome
(b) Centriole
(c) Plasma membrane
(d) Insects
(e) Genes
(f) Leucoplast

Solution C.1.

Protoplasm is the living matter of the cell. Protoplasm cannot be analysed chemically because the chemical composition of protoplasm is very complex. It varies slightly from one cell to another, although the common elements included in the composition of protoplasm such as carbon, hydrogen, oxygen, nitrogen, sulphur, iron and phosphorus are still the same in all the cells.

Solution C.2.

Organs of an organism are the parts of the body which have a definite shape and structure and perform specific functions. Cell organelles are also parts of the cell which have a definite shape and structure and perform specific functions. Organelles have the same status in a cell as the organs have in the entire body of an animal or a plant performing specific functions.

Solution C.3.

The cells of an elephant would be of the same size as the cells of a rat. The size of cells does not vary within the organisms, however, the number of cells varies from one organism to another. A larger animal like an elephant will have more number of cells as compared to a smaller animal like a rat. However, the size of the cell will be the same.

Solution C.4.

(a) Protoplasm and cytoplasm

Protoplasm Cytoplasm
(i) It is the living matter, the total substance of a living cell, i.e. the cytoplasm and the nucleus. (ii) It is a mixture of water and soluble organic and inorganic compounds, in which various cell organelles are embedded.

(b) Nucleolus and nucleus

Nucleolus Nucleus
(i) It is a round-shaped nucleoli present inside the nucleus. (ii) It is a dense spherical structure present in the cell that contains a network of thread-like structures called chromatin fibres.

(c) Centrosome and chromosome

Centrosome  Chromosome
(i) It is a clear area of cytoplasm close to the nucleus, from which spindle fibres develop during cell division.

(ii) Centrosome is found only in an animal cell.

(i) Chromosomes carry hereditary information or genes which transmit genetic characters from parents to offspring.

(ii) Chromosomes are found in the nucleus of both, animal and plant cells.

(d) Cell wall and cell membrane

Cell wall Cell membrane
(i) It is a non-living rigid layer. (i) It is a living, thin, flexible membrane.
(ii) It is made of cellulose. (ii) It is made of lipoproteins.
(iii) It is freely permeable. (iii) It is semi-permeable.

(e) Plant cell and animal cell

Plant cell Animal cell
(i) Cell wall is present. (i) Cell wall is absent.
(ii) Centrosome is absent. (ii) Centrosome is present.
(iii) Vacuoles are large and prominent. (iii) Vacuoles are small and temporary.
(iv) Plastids are present. (iv) Plastids are absent.

(f) Prokaryotes and eukaryotes

Prokaryotes Eukaryotes
(i) Organisms with cells containing a primitive, undefined nucleus are called prokaryotes. (i) Organisms with cells containing a well-defined nucleus with a nuclear membrane are called eukaryotes.
(ii) They contain small ribosomes. (ii) They contain larger ribosomes.
(iii) They lack other cell organelles. (iii) They contain other cell organelles.
(iv) Examples: Bacteria, blue-green algae (iv) Examples: Euglena, Human beings

Solution C.5.

Features found only in plant cells:

  1. Presence of cell wall
  2. Presence of large vacuoles. The liquid contained in vacuoles is called cell sap
  3. Presence of plastids

Features found only in animal cells:

  1. Presence of centrosome

Solution C.6.

Cells generally remain small in size because:

  1. To enable different regions of the cell to communicate with each other rapidly for the cell to function effectively
  2. To have a large surface area is to volume ratio for greater diffusion of substances, in and out of the cell

Solution D.1.

Postulates of cell theory:

  1. Cell is the smallest unit of structure of all living things.
  2. Cell is the unit of function of all living things.
  3. All cells arise from pre-existing cells.

Cell theory was propounded by Theodor Schwann and Matthias Schleiden in the year 1839 and was modified by Rudolf Virchow in 1858.

Solution D.2.

Living cell Brick in a wall
1. Non-rigid living structure 1. Rigid non-living structure
2. Mainly composed of cellulose 2. Mainly composed of soil
3. Freely permeable 3. Impermeable

Solution D.3.

Cells Plastid Pigment
(a) petals of sunflower Chromoplasts Xanthophyll
(b) ripe tomato Chromoplasts Carotene
(c) skin of green mango Chloroplasts Chlorophyll
(d) cells of potato Leucoplasts No pigment

Solution D.4.

(a) Plasma membrane:

  1. Separates contents of the cell from its surroundings
  2. Regulates the entry of certain solutes and ions
  3. Maintains the shape of animal cell

(b) Ribosome:

  1. Protein synthesis

(c) Lysosomes:

  1. Intracellular digestion
  2. Destroy foreign substances
  3. When the cell is old or injured, lysosomes rapidly destroy cell organelles and hence, are called suicide bags.

(d) Mitochondria:

  1. Synthesis of respiratory enzymes
  2. Release of energy from pyruvic acid produced in cytoplasm in the form of ATP

(e) Golgi apparatus:

  1. Synthesis and secretion of enzymes, hormones, etc.
  2. Formation of acrosome of sperm

(f) Cytoplasm:

  1. Different organelles contained in it perform different functions.
  2. All metabolic activities occur in it.

(g) Asters of centrosome:

  1. Initiates and regulates cell division
  2. Forms spindle fibres

(h) Chromosomes:

  1. Carry genetic characters from parents to offspring

(i) Glycogen granule:

  1. Serves as food for the cell

(j) Vacuoles:

  1. Gives turgidity to the cells
  2. Storage of water and other substances, food, pigments and waste products

Solution D.5.

Common features found in both plant and animal cells:

  1. Presence of cell membrane
  2. Presence of liquid matrix called cytoplasm in the cell
  3. Presence of mitochondria which produces energy
  4. Presence of ribosomes that synthesize proteins
  5. Presence of Golgi body
  6. Presence of a prominent nucleus

Solution E.1.

(a) Fig. B is a plant cell. It has a cell wall and a large vacuole which pushes the nucleus towards the periphery.
(b) Cell membrane, ribosomes, nucleus, endoplasmic reticulum, lysosomes, Golgi body and mitochondria are common to both the types.
(c) Plastids and cell wall are found only in plant cell. Centrosome is found only in animal cell.

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Selina Concise Biology Class 9 ICSE Solutions Introducing Biology

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Selina Concise Biology Class 9 ICSE Solutions Introducing Biology

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 1 Introducing Biology. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina ICSE Solutions for Class 9 Biology Chapter 1 Introducing Biology

Exercise 1

Solution A.

(a) (iv) fossils
(b) (iv) biotechnology

Solution B.1.

(a) Biotechnology
(b) Horticulture
(c) Palaeontology
(d) Immunology
(e) Ichthyology

Solution B.2.

(a) limbs, joints
(b) Genome
(c) silkworms
(d) origin, descent
(e) parasites
(f) Jeevaj (viviparous)
(g) Hippocrates

Solution B.3.

Column A Column B 
Ichthyology Fishes
Ornithology Birds
Ecology Environment
Virology Viruses
Herpetology Snakes
Palaeontology Fossils
Cytology Cells
Pathology Diseases

Solution B.4.

  1. Biotechnology
  2. Bioengineering

Solution B.5.

  1. Insects – Entomology
  2. Birds – Ornithology
  3. Fungi – Mycology
  4. Heredity – Genetics

Solution B.6.

  1. Biotechnologist
  2. Teacher
  3. Bacteriologist
  4. Druggist
  5. Dentist
  6. Entomologist

Solution C.1.

Biology is the study of living beings, all plants and animals including humans. Biology had flourished greatly in ancient India during 2500 B.C. to 650 B.C. The roots of biology can be traced back to pre-historic periods, when primitive man lived in jungles and caves. Biology has slowly grown through the ages, but developed very fast in the 20th century and is showing signs of even faster growth in the 21st century.

Solution C.2.

The knowledge of biology has greatly helped us in the field of human health. It helps us to understand the cause of many diseases. We are able to identify various micro-organisms that cause diseases in man. We can study their mode of living and the different ways in which they spread diseases. The understanding of disease-causing microorganisms has led to the development of new drugs, both natural and synthetic drugs that can kill these organisms.

Solution C.3.

A farmer, although has never studied biology, knows by his experience how to increase his produce. He knows how to plough and plant crops and select good quality seeds for sowing. He is also familiar with various methods of irrigation. He knows the technique of cross-breeding and removing weak and unwanted plants and cultivating improved varieties at the right time.

A housewife, by using her experience knows which fruit or vegetable to grow and for how much time. She also knows the nutritional values of various foodstuffs. A housewife adopts various principles of maintaining hygiene at home. She knows to tame some useful animals like cow, goat and dog for her maximum benefit.

Solution C.4.

(a) Zoology is the study of animals, whereas Entomology is the study of insects.

(b) Genetics is the science of transmission of body characteristics from parents to offspring, whereas Embryology is the study of formation and development of embryos of plants and animals.

(c) Botany is the study of plants, whereas Mycology is the study of fungi.

(d) Space Biology is the study of survival problems of living things in outer space, whereas Exobiology is the study of life elsewhere in the universe.

(e) Biotechnology is the use of living cells or micro-organisms in industry and technology, whereas Bioinformatics is the management and analysis of biological information stored in databases.

Solution D.1.

Yes, Biology can help in further increasing the yield of food. New varieties of plants and new breeds of cattle, poultry, etc. are being developed with the knowledge of biology. The science has also increased our knowledge of diseases of plants and animals, and how to cure them. All these efforts are helping us to produce more food in fields, dairies and poultry farms.

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Selina Concise Biology Class 9 ICSE Solutions Economic Importance Of Bacteria And Fungi

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Selina Concise Biology Class 9 ICSE Solutions Economic Importance Of Bacteria And Fungi

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 9 Economic Importance Of Bacteria And Fungi. You can download the Selina Concise Biology ICSE Solutions for Class 9 with Free PDF download option. Selina Publishers Concise Biology for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines.

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Selina ICSE Solutions for Class 9 Biology Chapter 9 Economic Importance Of Bacteria And Fungi

Exercise 1

Solution A.

  1. (d) they have no chlorophyll
  2. (b) Streptomyces
  3. (c) Bacillus
  4. (c) Rhizobium

Solution B.1.

The three common types of bacteria are:

  1. Cocci (spherical bacteria)
  2. Bacilli (rod-shaped bacteria)
  3. Spirilla (spiral bacteria)

Solution B.2.

Column A Column B
(i) Penicillium (b) Antibiotic
(ii) Diplococci (c) Bacteria occurring in pairs
(iii) Streptococci (a) Bacteria occuring in chains

Solution C.1.

No, bacteria and yeast are not considered as plants because they do not have chlorophyll and their mode of nutrition is not autotrophic, which are characteristic features of plants.

Solution C.2.

Bacteria may be present in the form of spores in the air.

Solution C.3.

Spore formation in bacteria is not considered as a form of reproduction because bacteria reproduce only asexually by means of fission or cell division. Spore formation is just a method of escaping unfavourable conditions.

Solution C.4.

Bacteria are unicellular organisms that lack membrane bound cell organelles like chloroplast, mitochondria, etc. and even a well-defined nucleus is absent which states that they have a simpler cellular organization.

Solution C.5.

(a) Decay and Putrefaction

Decay Putrefaction
1. It is the complete breakdown of organic matter by bacteria. 1. It is the incomplete breakdown of organic matter by bacteria.
2. Does not emit a foul smell 2. Emits a foul smell

(b) Pasteurization and Sterilization

Pasteurization Sterilization
1. Temperature- 60°C 1. Temperature- 110°C
2. Does not kill spores 2. Kills even spores
3. Partial sterilization 3. Complete sterilization
E.g. Pasteurization of milk E.g. Sterilization of canned food

Solution C.6.

Direct sunlight contains ultraviolet radiations of the sun, which help in killing of mould spores present in air.

Solution D.1.

Bacteria reproduce asexually by means of fission (binary fission), while yeast reproduces asexually by budding producing chains.

Solution D.2.

Role of micro-organisms in industrial production:

  1. Bacteria are used in the production of vinegar and in the processing of coffee, tobacco, etc.
  2. Different flavours of tea, coffee, etc. are produced by certain bacteria.
  3. Tanning of leather is basically brought about by sunlight, but there are a few micro-organisms which are involved in this process.
  4. Fibres used for making rope, linen, etc. are obtained by loosening the fibres of hemp and flax by retting, which involves the use of bacteria.
  5. Bacteria are used for the large-scale production of antibiotics, enzymes, hormones, serum, vaccines and toxoids.

Solution D.3.

Modes of nutrition in bacteria:

  1. Autotrophic bacteria: Able to synthesize their own food
    a. Photoautotrophs: Contain chlorophyll and use light energy for the synthesis of food
    b. Chemoautotrophs: Obtain energy by oxidizing inorganic compounds
  2. Heterotrophic bacteria: Require organic compounds as their main source
    a. Saprophytes: Grow on dead and decaying organic matter
    b. Parasites: Obtain their food from living host on which they grow

Solution D.4.

Uses of bacteria in industry:

  1. Tea curing: Certain bacteria are used to produce different flavours of tea.
  2. Tanning of leather: Tanning of leather is basically brought about by sunlight, but there are a few bacteria which are involved in this process.

Solution D.5.

Antibiotics are chemical substances produced by a living organism that kill or stop the growth of disease-causing micro-organisms such as fungi and bacteria.

Examples of antibiotics:

  1. Penicillin
  2. Streptomycin

Solution D.6.

No, tinned and sealed food are not always safe to eat as they may contain harmful bacteria like Clostridium botulinum, which may cause serious food poisoning resulting in Botulism. In extreme cases, this condition may even prove to be fatal for life.

Solution E.1.

(a) Soil bacteria such as Rhizobium are present in the root nodules of leguminous plants. These bacteria convert free nitrogen of the soil atmosphere to soluble nitrates.

(b) (i) Nitrosomonas converts ammonium compounds to nitrites.
(ii) Nitrobacter converts nitrites to nitrates.

(c) Denitrifying bacteria in the soil break down nitrates present in the soil to release nitrogen gas which enters the atmosphere.

(d) Nitrifying bacteria present in the soil convert nitrogenous wastes of animals and dead remains of plants and animals to ammonia. Ammonia is then converted to ammonium compounds. In this way, plants and animals help in the formation of ammonium compounds.

Exercise 2

Solution A.1.

  1. (b) Yeast
  2. (c) Spore formation
  3. (d) They do not have a true nucleus.
  4. (a) Ethyl alcohol

Solution B.1.

Solution C.1.

Rhizopus is the common bread mould. It grows not only on bread, but also on a variety of organic matter such as paper, wood, cloth, animal dung, leather goods and food materials such as fruit, bread, pickles, chapati, etc. particularly in warm and humid climate.

Solution C.2.

Direct sunlight contains ultraviolet radiations of the sun which help in killing of mould spores present in air.

Solution C.3.

Role of certain fungi in industrial production:

  1. Preparation of fermented foods and bakery products
  2. Preparation of alcoholic beverages
  3. Preparation of organic acids
  4. Production of enzymes
  5. Production of antibiotics
  6. Production of alcohol
  7. Production of wine
  8. Bread-making
  9. Cheese making
  10. Mushroom cultivation

Solution C.4.

Useful effects of wine:

  • In mild quantities, wine acts as a stimulant.
  • It can be used to stimulate hunger, reduce anxiety and improve digestion.

Harmful effects of wine:

  • In large quantities, wine can trigger asthma attack and increase blood pressure.
  • It can cause body ailments, particularly liver cirrhosis.

Solution C.5.

(a) Saprophyte and parasite

Saprophyte Parasite
Obtains nourishment from dead and decaying organic matter Obtains nourishment from the body of the living host

(b) Aerobic and anaerobic respiration with regard to products

Aerobic respiration Anaerobic respiration
Products – Carbon dioxide (CO2), water (H2O) and energy (ATP) Products – Ethanol (2C2H5OH), carbon dioxide (CO2) and energy (ATP)

(c) Decay and putrefaction

Decay Putrefaction
Complete breakdown of organic matter by bacteria without the emission of foul smell Incomplete breakdown of organic matter by bacteria along with the emission of foul smell

Solution D.1.

Antibiotics are chemical substances produced by a living organism that kill or stop the growth of disease-causing micro-organisms such as fungi and bacteria.

Examples of antibiotics:

  1. Penicillin
  2. Streptomycin

Solution D.2.

No, tinned and sealed food are not always safe to eat as they may contain harmful bacteria like Clostridium botulinum, which may cause serious food poisoning resulting in Botulism. In extreme cases, this condition may even prove to be fatal for life.

Solution D.3.

  • Bacteria can be present in an aquarium.
  • Bacteria are present everywhere; in air, soil, water and foodstuffs. They are found in boiling water and also below 0°C. They are present on the bodies of all living and non-living organisms. They live on readymade food. In short, they are omnipresent.
  • Bacteria are heterotrophic and may be decomposers or micro-aerobic in nature. Their mode of reproduction is very fast.

Solution E.1.

(a) Moulds are commonly present in air, water, etc. Hence, they were already present when moist bread was kept covered with the bell-jar.

(b) If bread was not covered with the bell-jar, moulds would have still appeared, but after some time. The warm and humid conditions inside the bell-jar promote rapid production of mould.

(c) Moulds do not grow below freezing point inside a refrigerator.

(d) Mycelia appear first on the bread.

(e) Bread mould obtains its nourishment through extracellular digestion from the substratum on which it grows. This mode of nourishment is called saprophytic nutrition.

Solution E.2.

Major steps in the cultivation of common edible mushrooms:

  1. Composting: Composting involves mixing of various components such as wheat or paddy straw, chicken manure and organic and inorganic fertilizers in a fixed proportion. The temperature of compost is maintained at around 50°C. The compost is kept undisturbed for about one week.
  2. Spawning: ‘Mushroom seed’ in the form of mycelium of mushroom to be grown is introduced into the heap of compost and left for spreading for around two days.
  3. Casing: Casing is the most important step of mushroom cultivation. It involves spreading of a thin layer of soil over the compost. This provides humidity and support to the mushroom. It also serves to prevent the desiccation of the compost heap and helps in temperature regulation at around 20°C-25°C to forbid the growth of pests and diseases. The provision for circulating air around the compost bed should also be made.
  4. Cropping and harvesting:Three major growth stages are observed, before mushrooms attain a fully grown form. Firstly, the mycelium, i.e. a network of fibrous mass, spreads out in 2 to 6 weeks, followed by the tiny pin head stage and finally the button stage, which is marked by an increase in the mushroom size, until it acquires marketable size.
  5. Preservation: Mushrooms have a very short shelf-life. Processes such as vacuum cooling, bombardment by gamma radiation, followed by storage at 15°C, freeze drying in a solution of citric acid, ascorbic acid and brine, etc. are used for the preservation of mushrooms.

Solution E.3.

a. Denitrifying bacteria are a boon to farmers because they curb the excess supply of nitrates to plants. Excessive nitrates can even harm the ecosystem as a whole because some wild plants like cultivated crops can thrive on nitrogen. Growth of these plants is favoured in nitrogen-saturated environments which can upset the ecosystem. Denitrifying bacteria are a curse to farmers because they breakdown soil nitrates to release free nitrogen gas into the atmosphere, thereby reducing the levels of nitrogenous compounds in the soil.
Yeast respires anaerobically in the absence of oxygen. It breaks down carbohydrates into simpler products such as ethanol by fermentation. The quality of alcohol produced varies with the kind of yeast employed.

b. During the baking process, yeast added to the dough ferments sugar and produces carbon dioxide. This causes the dough to rise, and when baked, the gas bubbles expand, giving the bread a light and spongy texture. Therefore, yeast is used in bakeries and breweries.

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