Selina ICSE Solutions for Class 9 Biology

Selina Concise Biology Class 9 ICSE Solutions Skin- “The Jack of All Trades”

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Selina Concise Biology Class 9 ICSE Solutions Skin- “The Jack of All Trades”

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 9 Chapter 13 Skin”The Jack Of All Trades”. 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 13 Skin- “The Jack of All Trades”

Exercise 1

Solution A.

  1. (d) the skin will turn dry and rough
  2. (b) Albinism, Leucoderma
  3. (c) Skin
  4. (b) Dermis
  5. (d) Palm

Solution B.1.

Hypothalamus, a portion of the forebrain is the principal body heat regulating centre in our brain.

Solution B.2.

Modified sweat gland: Mammary gland
Modified sebaceous gland: Ceruminous gland

Solution B.3.

Sebaceous glands

Solution C.1.

Functions of the mammalian skin other than those concerned with heat regulation:

  1. Storage of food: Skin acts as a storehouse of energy by storing reserve food in the form of fat in the hypodermis.
  2. Synthesis of Vitamin D: Skin has the ability to synthesize small quantity of Vitamin D in the presence of sunlight.

Solution C.2.

A peculiar roughness of the skin produced by cold or fear, in which the hair follicles become erect and form bumps on the skin is called goose flesh.

Goose flesh occurs when the muscles at the base of hair known as erectors or arrectors, contract. The erector muscles are obliquely placed between the hair follicle and the outer part of dermis. They are smooth muscles that are necessary to move the hair. The contraction of erector muscle pulls the hair vertical and depresses the epidermis, resulting in goose flesh.

Solution C.3.

Man is a warm-blooded mammal. Our body must maintain an average temperature of 98.6 degree Fahrenheit to function properly. When we feel too hot or too cold, our nervous system sends certain automatic and autonomic reflexes that help to keep us warm. In cold weather, the blood vessels get narrowed (vasoconstricted). Shivering occurs when our muscles expand and contract rapidly to produce extra body heat. The amount of heat produced is increased by increased metabolic rate and muscular activity, which occurs in the form of shivering. That is why, our body shivers and teeth chatter to protect from cold by generating more heat.

Solution C.4.

LeucodermaAlbinism
Loss of skin pigmentation from smaller or larger patches at different regions of the bodyComplete loss of pigmentation of the skin all over the body

Solution C.5.

Two glands found in the human skin are:

  1. Ceruminous gland: It is a modified sebaceous gland found in the auditory canal. It secretes wax-like substance called ear wax.
  2. Mammary gland: It is a modified sweat gland. It is related to reproductive hormones and pregnancy.

Solution C.6.

Fever and sickness or any kind of vigorous activity can lead to perspiration even in cold outside.

Solution D.1.

EpidermisDermis
1. Stratum corneum: It is the outermost layer having layers of flattened dead cells made up of horny protein called keratin.It consists of elastic fibres, blood vessels, nerves, etc.
2. Granular layer: It is very thin middle layer having two or three sublayers of flattened cells.
3. Malpighian layer: It is the innermost region of the epidermis. The cells can actively divide to produce new cells.

Solution D.2.

Vasodilation: Dilation of blood vessels in the skin leading to an increase in the blood supply.
Vasoconstriction: Narrowing of blood vessels leading to reduction in the blood supply to the skin.
Temperature regulation in cold weather:

  1. At low temperature, the blood vessels get narrowed or vasoconstricted. This reduces the blood supply to the skin.
  2. There is less loss of heat by convection, conduction and radiation. There is less loss of heat through vapourization as reduced blood supply lowers the secretion of sweat by sweat glands.

Selina Concise Biology Class 9 ICSE Solutions Skin- “The Jack of All Trades” 1

Temperature regulation in hot weather:

  1. At high temperature, the blood supply to the skin is increased by vasodilation or dilation of blood vessels in the skin.
  2. This results in greater loss of heat by convection, conduction and radiation.There is more loss of heat through vapourization as more sweat is secreted due to rich supply of blood to the skin.

Solution D.3.

(a) Entry of germs: Skin prevents the entry of harmful substances or infectious agents inside the body.
(b) Excessive loss of heat in severe cold: Skin prevents energy loss from the body. It conserves body heat in cold weather and facilitates loss of heat in hot weather.
(c) Entry of harmful ultra-violet rays: Skin protects the body against harmful ultraviolet light.

Solution E.1.

Selina Concise Biology Class 9 ICSE Solutions Skin- “The Jack of All Trades” 2

Solution E.2.

(a)

  1. Sweat pore
  2. Sebaceous gland
  3. Sweat gland
  4. Fat
  5. Dermis
  6. Stratum malpighian
  7. Stratum corneum
  8. Epidermis
  9. Hair

(b)

  • Function of part 2 (Sebaceous gland): It produces oil called sebum, which plays a role in keeping our skin moist.
  • Function of part 4 (Fat): The skin reserves food in the form of a layer of fat.
  • Function of part 3 (Sweat gland): It secretes a transparent liquid (sweat) containing water and salts from the body in order to regulate body temperature.
  • Function of part 9 (Hair): Hair provide a sensation of touch and are also helpful in forensic investigations.

Part which has at least three functions:
Sebaceous gland:

  1. Skin protection
  2. Secretes an oily substance known as sebum that lubricates hair and skin of mammals
  3. Presence of sebum enables to experience a wet skin even when we have not taken bath for days

(c) The one function which may be common to both men and women is that the fat serves as a food reserve and heat insulating layer as well as a shock absorber.

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Selina Concise Biology Class 9 ICSE Solutions Hygiene – A Key To Healthy Life

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Selina Concise Biology Class 9 ICSE Solutions Hygiene – A Key To Healthy Life

APlusTopper.com provides step by step solutions for Selina Concise ICSE Solutions for Class 9 Biology Chapter 9 Chapter 15 Hygiene A Key To Healthy 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 15 Hygiene – A Key To Healthy Life

Exercise 1

Solution A.

  1. (d) cholera
  2. (d) Sharing towels with others
  3. (d) Plasmodium
  4. (c) Fluorides
  5. (b) Bacteria

Solution B.1.

Column IColumn II (Answers)
(a) Mosquito(iv) Malaria
(b) Plasmodium(iii) Vector
(c) Entamoeba histolytica(v) Dysentery
(d) Aedes mosquito(ii) Dengue
(e) Insecticide(i) DDT

Solution B.2.

(a) Vectors (disease carriers)
(b) Pathogens
(c) Hygiene

Solution B.3.

The different ways by which the housefly contaminates our food:

  1. Hairy body and legs: Hairy or spiny body and legs easily pick up dirt containing germs from unhygienic places such as rotten materials, infected wound or faecal matter. When these flies sit on our food, they rub their legs continuously dropping the particles of dirt onto the food, thereby contaminating it.
  2. Pouring out saliva: When the housefly pours its saliva or regurgitates on food, foodstuffs get moistened and pathogens get deposited on them. This results in their contamination.
  3. Excreta: While feeding on food items, houseflies may deposit their excreta on food, contaminating it.
  4. Direct transmission of germs: In some cases, houseflies directly transmit the pathogens. In case of eye disease trachoma, pathogens are transferred from an infected person to a healthy person, when a fly settled on an infected eye of a person sits on the eyes of a healthy person.

Solution B.4.

Two methods of controlling flies:

  1. Spraying of insecticides
  2. Elimination of breeding grounds

Solution B.5.

Effective methods for controlling mosquitoes:

  1. Spraying insecticides
  2. Food should be protected by covering it
  3. Eliminating breeding places of mosquitoes

Solution B.6.

Kind of mosquitoDisease caused by it
AnophelesMalaria
CulexFilariasis

Solution B.7.

Contamination of potable water can occur due to

  • Improper disposal of sewage
  • Defecation and urination near lakes, rivers or ponds
  • Drainage of animal wastes and washings from dairies and poultries into water bodies

Solution C.1.

(i) One should breathe by nose and never by mouth because nose contains hair and mucous to trap dust and micro-organisms, so that the inhaled air becomes pure and the respiratory passage is free of dust and micro-organisms.

(ii) We handle a variety of things like books, coins, furniture, tools and machinery in workshops, seats and supporting rods in buses and even pets and other domestic animals in our day-to-day life. Many of these objects carry germs. These germs can be picked up by us, when we touch these objects and get transferred to other parts of our body or into our mouth, when we eat our food. Therefore, it is necessary to wash our hands before eating food to avoid the spread of diseases caused due to these germs.

(iii) Flies are carriers of many disease-causing germs and bacteria. Therefore, eating places must be kept free of flies to avoid possible contamination of food.

Solution C.2.

Cockroaches and rats are common household pests.

  1. Cockroaches are involved in spoiling food, paper and cloth. They may act as carriers of viruses, especially those which cause cancer.
  2. Rats eat grains and other foods. They also act as carriers of certain pathogens. A parasite named rat-fleas lives on rat’s skin. It possibly carries the germs of plague.

Solution C.3.

TYPE OF DYSENTERYCAUSATIVE GERMPRECAUTION
1. Bacillary dysenteryBacterium: ShigelladysenteriaeDrinking safe (boiled) water
2. Amoebic dysenteryProtozoan: EntamoebahistolyticaAvoiding contaminated water and food

Solution C.4.

Symptoms of Hepatitis:

  • Body ache
  • Yellow eyes
  • Deep yellow urine
  • Enlarged liver

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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 AColumn 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

DecayPutrefaction
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 smell2. Emits a foul smell

(b) Pasteurization and Sterilization

PasteurizationSterilization
1. Temperature- 60°C1. Temperature- 110°C
2. Does not kill spores2. Kills even spores
3. Partial sterilization3. Complete sterilization
E.g. Pasteurization of milkE.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

SaprophyteParasite
Obtains nourishment from dead and decaying organic matterObtains nourishment from the body of the living host

(b) Aerobic and anaerobic respiration with regard to products

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

(c) Decay and putrefaction

DecayPutrefaction
Complete breakdown of organic matter by bacteria without the emission of foul smellIncomplete 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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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 AColumn B 
IchthyologyFishes
OrnithologyBirds
EcologyEnvironment
VirologyViruses
HerpetologySnakes
PalaeontologyFossils
CytologyCells
PathologyDiseases

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 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

ProtoplasmCytoplasm
(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

NucleolusNucleus
(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 wallCell 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 cellAnimal 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

ProkaryotesEukaryotes
(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 cellBrick in a wall
1. Non-rigid living structure1. Rigid non-living structure
2. Mainly composed of cellulose2. Mainly composed of soil
3. Freely permeable3. Impermeable

Solution D.3.

CellsPlastidPigment
(a) petals of sunflowerChromoplastsXanthophyll
(b) ripe tomatoChromoplastsCarotene
(c) skin of green mangoChloroplastsChlorophyll
(d) cells of potatoLeucoplastsNo 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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