Category: Class 12 Biology

NCERT  Solutions For Class 12 Biology Biotechnology: Principles And Processes

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 11 Biotechnology: Principles And Processes:

Section Name	Topic Name
11	Biotechnology:Principles And Processes
11.1	Principles of Biotechnology
11.2	Tools of Recombinant DNA Technology
11.3	Processes of Recombinant DNA Technology
11.4	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Can you list 10 recombinant proteins which are used in medical practice? Find out where they are used as therapeutics (use the internet).
Ans: (i) Human insulin – Diabetes
(ii) Human growth hormone – Dwarfism cure
(iii) Blood clotting factor Y1H/IX-Haemophilia
(iv) TPA (tissue plasminogen activator) – Heart attack/strokes
(v) PDGF (platelet derived growth factor) – Stimulates wound healing.
(vi) Interferon – Treatment of viral infection.
(vii) Interlinking – Enhances immune reaction,
(viii) Hepatitis B vaccine – Prevention of infectious disease.
(ix) Herpes Vaccine – Prevention of infectious disease.
(x) DNase I – Treatment of cystic fibrosis.

2. Make a chart (with diagrammatic representation) showing a restriction enzyme, the substrate DNA on which it acts, the site at which it cuts DNA and the product it produces.
Ans: Name of the Restriction enzyme – Bam HI.
The substrate DNA on which it acts –

3. From what you have learnt, can you tell whether enzymes are bigger or DNA is bigger in molecular size? How did you know?
Ans: Both DNA (deoxyribonucleic acid) and enzymes are macromolecules. DNA is a polymer of deoxyribonucleotides and enzymes are proteins hence these are polymers of amino acids. But DNA is bigger in molecular size as compared to proteins because synthesis of proteins is regulated by a small segment of DNA, called genes and also a large number of proteins can be synthesised by a DNA molecule.

4. What would be the molar concentration of human DNA in a human cell? Consult your teacher.
Ans: The molar concentration of DNA in human cell is 2 mg/ml of cell extract.

5. Do eukaryotic cells have restriction endonucleases? Justify your answer.
Ans: No, eukaryotic cells do not have restriction endonuclease because DNA molecules of eukaryotes are heavily methylated. All the restriction endonucleases have been isolated from various strain of bacteria.

6. Besides better aeration and mixing properties, what other advantages do stirred tank bioreactors have over shake flasks?
Ans: Shake flasks are used for growing and mixing the desired materials on a small scale in the laboratory. A large scale production of desired biotechnological product is done by using ‘bioreactors’. Besides better aeration and mixing properties, the bioreactors have following advantages
(i) Small volumes of cultures are periodically withdrawn from die reactor for sampling.
(ii) It has a foam control system, pH control system and temperature control system.
(iii) Facilitates even mixing and oxygen availability throughout the bioreactor.

7. Collect 5 examples of palindromic DNA sequences by consulting your teacher. Better try to create a palindromic sequence by following base-pair rules.
Ans: Palindrome nucleotide sequences in the DNA molecule are groups of bases that form the same sequence when read both forward and backward. Five examples of palindromic DNA sequences are as follows:
(i) 5′-—————GGATCC——————3’
3′—————CCTAGG—————–5′
(ii) 5’—————AAGCTT——————3′
3′——————TTCGAA —————-5′
(iii) 5′—————–ACGCGT—————–3′
3′——————TGCGGA————– 5′
(iv) 5′———- ACTAGT————3′
3′——————TGATCA————5′
(v) 5′—————AGGCCT—————3′
3′——————TCCGGA————–5′

8. Can you recall meiosis and indicate at what stage a recombinant DNA is made?
Ans: Recombinant DNA is formed due to crossing over between non-sister chromatids of homologous chromosome. It occurs during pachytene stage of prophase of meiosis I

9. Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign DNA in addition to a selectable marker?
Ans: A reporter enzyme can be used to differentiate transformed cells by tracking down the activity of its co-responding genes (receptor gene). For e.g., (3-galactosidase (Lac Z) activity is not found in transformed cells so that they appear white in colour. The others, which appear blue in colour, indicate that cells do not carry foreign DNA.

10. Describe briefly the followings:
(a) Origin of replication
(b) Bioreactors
(c) Downstream processing
Ans: (a) Origin of Replication: This is a sequence from where replication starts and any piece of DNA when linked to this sequence can be made to replicate within the host cells. This sequence is also responsible for controlling the copy number of the linked DNA. So, if one wants to recover many copies of the target DNA it should be cloned in a vector whose origin support high copy number.

(b) Bioreactor: Bioreactors can be thought of as vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cell and/or their enzymes. The bioreactor provides optimum growth conditions and facilitates achieving the desired products. The most commonly used bioreactor is of stirring type. A stirred tank bioreactor is usually a cylindrical vessel or vessel with a curved base to facilitate mixing of the contents. In the sparged stirred tank bioreactor, sterile air bubbles are sparged. The stirrer facilitates the mixing and oxygen availability throughout the bioreactor. A bioreactor has an agitator system, an oxygen delivery system, a foam control system, a temperature control system, pH control system and sampling ports.

(c) Downstream Processing : The product obtained is subjected to a series, of processes collectively called downstream processing before it is made into a finished product ready for marketing. The two main processes are separation and purification. The product is then formulated with suitable preservatives. Such formulations have to undergo clinical trials, in case of drugs.

11. Explain briefly
(a) PCR
(b) Restriction enzymes and DNA
(c) Chitinase
Ans: (a) PCR = Polymerase chain reaction (in vitro method) is a molecular biological technique for enzymatically replicating DNA without using a living organism, such as E. coli or yeast.
3 steps in PCR are –
(i) Denaturation of desired double strand DNA-to ssDNA.
(ii) Annealing of primer to ssDNA (single standard).
(iii) Extension of primer by Taq DNA polymerase isolated form Thermits aquaticus.
Uses – Amplification of desired gene/gene cloning.
Advantage- More output, greater efficiency, less error prone, less human interference and cyclic and automated.
(b) Restriction enzymes and DNA – Restriction enzymes is a group of enzymes used to cleave or cut DNA strands each having a characteristics base sequence at which it cleaves.
(i) It restricts foreign DNA from entering normal cell by digesting it at various recognition site. Recognition site is palindromic.
(ii) They are endonuclease and exonuclease both types.
(iii) They produces sticky ends. Cleavage site and recognition site are different from each other. Restriction enzymes therefore are believed to be a mechanism evolved by bacteria to resist viral attack and to help in the removal of viral sequences.
(c) Chitinase – Chitinase is a enzyme to digest or breakdown glycosidic bonds in chitin cell wall of fungal cell to facilitate its transformation.

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NCERT Solutions For Class 12 Biology Reproduction in Organisms

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 1 Reproduction in Organisms:

Section Name	Topic Name
1	Reproduction in Organisms
1.1	Asexual Reproduction
1.2	Sexual Reproduction
1.3	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Why is reproduction essential for organisms?
Ans: Reproduction is the ability of living organisms to produce a young one similar to itself. It ensures continuity of a species generation after generation. Reproduction introduces variation in the organisms. Useful variations are essential for adaptation and evolution. Therefore, it is essential for organisms.

2. Which is a better mode of reproduction sexual or asexual? Why?
Ans: Sexual reproduction is a better mode of reproduction because of the following reasons:

1. Variation : Since fusion of gametes from different parents occur during sexual reproduction, hence genetic recombination takes place causing variations.
2. Evolution : Variation being a major factor of natural selection, therefore, it plays an important role in evolution.
3. Adaptation : The offspring produced due to sexual reproduction adapt better to the changing environmental conditions.
4. Vigour and Vitality : Genetic recombination, interaction, etc. during sexual reproduction provide vigour and vitality to the offspring.

3. Why is the offspring formed by asexual reproduction referred to as clone?
Ans: Asexual reproduction is a type of reproduction in which a single individual is capable of producing offspring. These offspring are not only genetically and morphologically similar to one another but also similar to their parent. Clone is the term given to individuals that are genetically and morphologically similar. Thus the offspring produced by asexual reproduction are called clones.

4. Offsprings formed due to sexual reproduction have better chances of survival. Why? Is this statement always true?
Ans: The offsprings obtained from sexual reproduction have better chances of survival because the genetic material of such organisms are formed from both the parents. Daughter organisms/offsprings show variation that leads to the evolution of species.

This statement is always true. The offspring produced due to sexual reproduction adapt better to the changing environmental conditions. Genetic recombination, interaction, etc. during sexual reproduction provide vigour and vitality to the offspring.

5. How does the progeny formed from asexual reproduction differ from those formed by sexual reproduction?
Ans: Production of offspring by a single parent without the formation and fiision of gametes is called asexual reproduction. It involves only mitotic cell division that gives rise the daughter cells which are genetically identical to the parent cell. Sexual reproduction is the production of offspring by two parents, male and female. It involves meiotic cell divisions producing haploid nuclei which on fusion produce offspring that are genetically different from their parents.

6. Distinguish between asexual and sexual reproduction. Why is vegetative reproduction also considered as a type of asexual reproduction?
Ans: The difference between asexual and sexual reproduction are as follows :

In plants asexual reproduction is called vegetative reproduction because vegetative plant parts like rhizome, runner, sucker, tuber, bulb all are capable of producing off springs These parts give rise to daughter individuals without the involvement of two parents.

7. What is vegetative propagation? Give two suitable examples.
Ans: Vegetative propagation is the formation of new plants from vegetative units. In plants, the units of vegetative propagation are runner, rhizome, sucker, tuber, offset, bulb, etc. These are capable of producing new offsprings. These structures are called v vegetative propagules.

Modified tuberous roots of sweet potato, tapioca, yam, Dahlia and Tinospora can be propagated vegetatively when planted in soil. Small plants emerging from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger are other examples.

8. Define:
(a)Juvenile phase
(b)Reproductive phase
(c)Senescent phase.
Ans: (a)Juvenile phase : All organisms have to reach a certain stage of growth and maturity in their life before they can reproduce sexually. That period of growth is called juvenile phase. However, this phase is known as vegetative phase in plants. This phase is of different durations in different organisms.
(b)Reproductive phase: The end of juvenile/ vegetative phase marks the beginning of reproductive phase. During this phase, the organisms produce offspring. In higher plants, this phase can be easily seen when they come to flower but in animals, the juvenile phase is followed by morphological and physiological changes prior to active reproductive behaviour. The reproductive phase is also of variable period in different organisms like some plants, flower throughout the year while others show seasonal flowering. In animals like birds lay eggs seasonally “but when in captivity (as in poultry farms) can be made to lay eggs throughout the year. Placental female mammals, undergo cyclical changes in reproductive organs during this phase.
(c) Senescent phase: It begins from the end of the reproductive phase. During this phase of life span, there is progressive deterioration in the body (like slowing of metabolism, etc.). Old age ultimately leads to death.

9. Higher organisms have resorted to sexual reproduction in spite of its complexity. Why?
Ans: Higher organisms have resorted to sexual reproduction in spite of its complexity because sexual reproduction results in multiplication and perpetuation of species and also contributes to evolution of species by introducing variation much more faster than asexual reproduction in a particular population. Sexual reproduction enables higher organisms to survive during unfavourable conditions.

10. Explain why meiosis and gametogenesis are always interlinked?
Ans: Gametogenesis is the process of formation of two types of haploid gametes (male and female). In gametogenesis, gametes are haploid in number and formed by meiosis so the chromosome number is haploid. Thus gametogenesis is always linked with meiosis.

11. Identify each part in a flowering plant and write whether it is haploid (n) or diploid (2n).
(a)Ovary ————————
(b)Anther ————————
(c)Egg ————————
(d)Pollen ————————
(e)Male gamete ————————
(f)Zygote ————————
Ans: (a)2n (b)2n (c)n (d)n (e)n (f)2n

12. Define external fertilization. Mention its disadvantages.
Ans: When fusion of the gametes takes place outside the body of the organisms, it is called external fertilization or external syngamy. The external medium like water is required for this form of fertilization. This form, is found in many aquatic animals like fishes, amphibians, majority of algae.
In this, parents release eggs and sperms in the surrounding water, then fertilization and development of offspring occur externally. Disadvantages of external fertilization:
(i)if occurs only in aquatic medium.
(ii)A chance factor is involved requiring synchronous release of gametes nearby and absence of turbulence of water.
(iii)There is no protection to young ones. They are vulnerable to a number of predators.

13. Differentiate between a zoospore and a zygote.
Ans: The zoospore is flagellated, motile, haploid or diploid spore formed inside a zoosporangium. It is the result of asexual reproduction.

The zygote is always diploid and formed by the fusion of gametes. It is usually non- flagellated and non-motile or motile. It is the net result of sexual reproduction.

14. Differentiate between gametogenesis from embryogenesis.
Ans: Differences between gametogenesis and embryogenesis are as follows :

15. Describe the post-fertilization changes in a flower.
Ans: In sexual reproduction, events that occur after the formation of zygote are called post-fertilization events. In flowering plants, the zygote is formed inside the ovule. After fertilization the sepals, petals and stamens of the flower wither and fall off. But the pistil remains attached to the plant. The zygote develops into the embryo and the ovules develop into the seed. The ovary develops into die fruit that develops.a thick wall called pericarp which is protective in – function. After dispersal, seeds germinate under favourable conditions to produce new plants.

16. What is % bisexual flower? Collect five bisexual flowers from your neighbourhood and with the help of your teacher find out their common and scientific names.
Ans: Flowers in which male and female sex organs (stamens and carpels) are borne on the same flowers are called bisexual flowers. You can observe following bisexual flowers in your kitchen and colony gardens :
(i)Brassica (sarson) – Brassica campestris
(ii)Onion – Allium cepa
(iii)Garden Pea (Edible pea) – Pisum sativum
(iv)Petunia – Petunia hybrida
(v)China rose (shoe flower) – Hibiscus rosa- sinensis.

17. Examine a few flowers of any cucurbit plant and try to identify the staminate and pistillate flowers. Do you know any other plant that bears unisexual flowers?
Ans: The male or staminate flowers of cucurbits bear bright coloured petals and a prominent group of stamens. Male plants or staminate flowers do not bear fruits. The female or pistillate flowers bear fruits. In a fertilised young pistillate flower very small fruit is visible below petals and sepals. Some unisexual plants are : Papaya, Mulberry and Date-palm.

18. Why are offspring of oviparous animals at a greater risk as compared to offspring of viviparous animals?
Ans: On the basis of the development of the zygote, animals are grouped into oviparous and viviparous. The oviparous animals such as reptiles and birds lay eggs. Their fertilised eggs are covered by hard calcareous shell and are laid in a safe place in the environment. After incubation period, young ones hatch out. In viviparous animals such as majority of mammals including human beings, the zygote develops into a young one inside the body of the female individual. After a certain growth period, the young ones are delivered by the female individual. Due to proper care and protection, the chances of survival of young ones are more in viviparous individuals. Oviparous offsprings are at a greater risk than viviparous ones.

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NCERT Solutions For Class 12 Biology Biodiversity and Conservation

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 15 Biodiversity and Conservation:

Section Name	Topic Name
15	Biodiversity and Conservation
15.1	Biodiversity
15.2	Biodiversity Conservation
15.3	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Name the three important components of  biodiversity.
Ans: Three components of biodiversity are:
(a) Genetic diversity
(b) Species diversity
(c) Ecological diversity

2. How do ecologists estimate the total number of species present in the world?
Ans: Ecologists estimate the total number of species present in the world by comparing species richness of some exhaustively studied groups between any two regions (tropics, temperate or polar regions). Species richness, as a measure of diversity, has been used by many ecologists. Species density or the number of species per m² is most commonly used to measure species richness. Species abundance and species proportional abundance based indices are some other alternative approaches to the measurement of diversity.

3. Give three hypothesis for explaining why tropics ’”show greatest levels of species richness.
Ans: (1) The tropical area have a more stable climate than temperate zones. Local species continues to live in absence of natural disturbances.
(2) Warm temperature and high humidity in most tropical areas provide favourable conditions for growth and survival of diverse species.
(3) Tropical areas receive more solar energy over year and thus tropical communities are more productive and can support a wide range of species.

4. What is the significance of the slope of regression in a species-area relationship?
Ans: Slope of regression or regression coefficient makes it easier to measure species richness along an area. For a limited area like, a country, it gives a constant value of 0.1 to 0.2 irrespective of the taxonomic group or region. It remains amazingly similar for all those small regions. On the contrary, for measuring species-area relationship over large areas like the entire continents, the slope of regression values in the range of 0.6 to 1.2.

5. What are the major causes of species losses in a geographical region?
Ans: Species are lost in a geographical region due to natural disturbances like forest fires; famine, drought and also due to human disturbance with over replantation, habitat destruction, habitat displacement, over specialization, intensive agriculture and pollution.

6. How is biodiversity important for ecosystem functioning?
Ans: Biodiversity is important for ecosystem functioning because,
(1) It contributes to productivity.
(2) It cause more efficient recycling of energy and matter.
(3) It has many alternative pathways for survival under diverse conditions.
(4) Rich biodiversity provides alternatives available at each trophic level. All organisms are linked in food chains and interact with their abiotic environment in such a way so as to keep the natural cycles going and make the ecosystems self – sustaining units. Disappearance of any link in a food chain will not affect the ecosystem as other alternatives are there.

7. What are sacred groves? What is their role in conservation?
Ans: Sacred forests or sacred groves are forest patches around places of worship which are held in high esteem by tribal communities. They are the most undisturbed forest patches which are often surrounded by highly degraded landscapes. They are found in several parts of India, e.g., Karnataka, Maharashtra, Rajasthan (Aravalli), Madhya Pradesh (Sarguja, Bastar), Kerala, Meghalaya. Temples built by tribals are found surrounded by deodar forests in Kumaon region, Jaintias and Khasjas in Meghalaya. Not a single branch is allowed to be cut from these forests. As a result many endemic species which are rare or have become extinct elsewhere can be seen to flourish here. Bishnois of Rajasthan protect Prosopis cineraria and Black Buck religiously. Some water bodies are also held sacred in certain places, e.g., Khecheopalri in Sikkim. Their aquatic flora and fauna are naturally preserved.

8. Among the ecosystem services are control of floods and soil erosion. How is this achieved by the biotic components of the ecosystem?
Ans: Ecosystem services are products or benefits given by ecosystem processes to the environment for its purification, beauty, biodiversity, protection of natural resources, habitat to wild life and tribals, protection of soils, CO₂ – O₂ balance, retention of water against floods, drought and pollution. Plants play a vital role in the control of floods and soil erosion. Their roots bind the soil 10. particles firmly and in this way they do not allow the top soil to be drifted away by winds or moving water. Roots of plants also make the soil porous and allow water to go into the soil.

9. The species diversity of plants (22 per cent) is much less than that of animals (72 per cent). What could be the explanations to how animals achieved greater diversification?
Ans: Species diversity refers to the variety of species within a region which is less in plants as compared to animals. It is due to greater dispersal/more number of surviving individuals. Most animals possess simple or complex nervous system to control and coordinate various activities. They possess receptors to receive against them. Most of their responses are adaptive and ensure their survival in changing environmental conditions. They, therefore, have evolved to reveal much higher species diversity than plants who do not possess nervous system and respond differently against environment stimuli.

10. Can you think of a situation where we deliberately want to make a species extinct? How would you justify it?
Ans: Humans can cause extinction of species through various means. We are trying to eradicate disease causing organisms (e.g., poliovirus) from this world to make this world disease free. Since such micro-organisms are harmful to the human society, such attempt is justified. Further, such micro-organisms are not essential components (producers or decomposers) of any ecosystem, and losing one or few such organisms would not affect the functioning of ecosystem.

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NCERT Solutions For Class 12 Biology Organisms and Populations

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 13 Organisms and Populations:

Section Name	Topic Name
13	ORGANISMS AND POPULATIONS
13.1	Organism and Its Environment
13.2	Populations
13.3	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. How is diapause different from hibernation?
Ans: Diapause is a period of suspended growth or development occuring in many insects and other invertebrates during which metabolic activities are greatly reduced. On the other hand, hibernation is a sleep like state in which a few animals, such as fishes and amphibians, pass the winter season as a way of surviving food scarcity and cold weather.

2. If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?
Ans: When a marine fish is placed in a fresh water aquarium, the fish will not be able to survive because marine fish is adapted to live in saline seawater. In fresh water, it will not be able to cope with the outside hypotonic environment because of osmoregulation problem. In fresh water, the concentration of water, the difference between the concentration of the water and inside of the fish are increased and therefore, the osmotic pressure is also increased.The fish has to take more water into the body to be able to survive and to get rid of the excess salt present in its body.

3. Define phenotypic adaptation. Give one example.
Ans: Phenotypic adaptations are non-genetic changes
occurring in living organisms due to various extreme environmental conditions, such as stress, extreme temperature, change of habitat. These includes acclimatization, behavioural changes, etc.

4. Most living organisms cannot survive at temperature above 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C?
Ans: Micro-organisms of hot.springs and vents (mouth of sea bed volcanoes) are able to survive at the high temperature due to
(i) occurrence of branched chain lipids in their cell membrane that reduce fluidity of cell membranes.
(ii) having minimum amount of free water in their bodies. Removal of water provides resistance to high temperature.

5. Last the attributes that populations but not individuals possess.
Ans: Some significant attributes that populations but not individual possess are –
(i) Natality
(ii) Mortality
(iii) Growth forms
(iv) Population density
(v) Population dispersion
(vi) Population age distribution
(vii) Sex ratio

6. If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?
Ans: If the population growing exponentially double in size in 3 years, the intrinsic rate of increase of this population will be towards maximum.

7. Name important defence mechanisms in plants against herbivory.
Ans: There are various defence measures for animals against predators. But plants, as they cannot move away, have certain defence mechanisms against herbivory. Their main defences are chemical toxins, such as strychnine, a poison produced by tropical vine, morphine by opium poppy, nicotine produced by tobacco plant. Apart from these chemicals, the common defence measure is presence of spines (modified leaves) on the leaves, stems of the plant, modifications of leaves into thorns, development of sharp silicated edges in leaves which prevent them against damage caused by herbivores.

8. An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Ans: An orchid plant is growing on the branch of a mango tree is called epiphyte, i.e., plants growing on other plants or trees. This type of interaction is known as commensalism, where in orchid / derives benefit of interaction whereas mango tree is not affected. The orchid growing on the branch of mango tree get more light to grow and also, the mango is not harmed in any way.
Commensalism can be defined as an interaction between two animal or plant species that habitually live together in which one species benefits from the association while the other is not significantly affected.

9. What is the ecological principle behind the biological control method of managing with pest insects?
Ans: The ecological principle behind the biological control method of managing with pest insects is predator – prey relationship. It is based on the ability of the predator to regulate prey population.

10. Distinguish between the following:
(a) Hibernation and Aestivation
(b) Ectotherms and Endotherms
Ans:

11. Write a short note on
(a) Adaptations of desert plants and animals
(b) Adaptations of plants to water scarcity
(c) Behavioural adaptations in animals
(d) Importance of light to plants
(e) Effect of temperature or water scarcity and the adaptations of animals.
Ans: (a) Desert plants have very small leaves or no leaves at all, and carrying out photosynthesis through the stems. Their stem could become succulent, and can store and retain water. Animals living in hot climatic region tend to be smaller than those living in cold climates. This can be explained by the fact that the amount of heat gained from the environment is approximately proportional to the body surface area. The majority of animals living in desert are small, like kangaroo rat. It feed on dry seeds and other dry plant material and does not drink,

(b) The evergreen trees such as Rhododendron, show water scarcity by an inward curling of the leaves. A more significant response is the closure of stomata, which reduces transpiration, but raises the internal temperature of die leaf affecting the rate of synthesis of proteins and photosynthesis. Deciduous trees of the temperature region drop their leaves in autumn, avoiding winter drought. Some water stressed plant’s accumulate excessive amounts of inorganic ions.

(c) Migrating temporarily to a less stressful habitat forms a more stressful habitat is a kind of behavioural adaptation in animals which enables them to survive in better environmental conditions. Desert lizards regulate their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature decreases below the optimum, but move into shady or underground places when the temperature of the surrounding area starts increasing.

(d) Light affects plants through its quality, intensity and duration. Duration of light affects phenology, photosynthesis, growth, reproduction, flowering. Quality of light influences flowering, seed germination and movements. Light is required for the production of chlorophyll in chloroplasts. Plants germinated under insufficient illumination causes the destruction of chlorophyll.

(e) Animals mainly are of two types as they are adapted to controlling their body temperature. Poikilothermous are the animals whose temperature fluctuates with that of the environment, e.g., invertebrates and vertebrates, other than birds and animals. In contrast, homeotherms are the animals which can maintain their body temperature at a constant level, e.g., birds and mammals.

12. List the various abiotic environmental factors.
Ans: Abiotic factors are non living factors and conditions of the environment which influence survival, function and behaviour of organisms. Various abiotic factors are :

(i) Temperature – Temperature is one of the most important environmental factors. The average temperature varies seasonally. It ranges from subzero level in polar areas and high altitudes to more than 50°C in tropical deserts in summer and exceeds 100°C in thermal springs and deep-sea hydrothermal vents.

(ii) Water – Next to temperature, water is the most important factor which influences the life of organisms. The productivity and distribution of land plants are dependent upon availability of water. Animals are adapted according to the water availability. E.g., aquatic animals are ammonotelic while xerophytic animals excrete dry feces and concentrated urine.

(iii) Light – Plants produce food through photosynthesis for which sunlight is essential source of energy. Light intensity, light duration and light quality influences the number of life processes in organisms, such as – photosynthesis, growth, trans-piration, germination, pigmentation, movement and photoperiodism.

(iv) Humidity – Humidity refers to the moisture (water vapour) content of the air. It determines the formation of clouds, dew and fog. It affects the land organisms by regulating the loss of water as vapour from their bodies through evaporation, perspiration and transpiration.

(v) Precipitation – Precipitation means rainfall, snow, sleet or dew. Total annual rainfall, seasonal distribution humidity of the air and amount of water retained in the soil are the main criteria that limit the distribution of plants and animals on land.

(vi) Soil – The soil is one of the most important ecological factor called the edaphic factor. It comprises of different layers called horizons. The upper weathered humus containing part of soil sustains terrestrial plant life.

13. Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of the benthic zone
Ans: (a) Man, (Homo sapiens)
(b) Black bear
(c) Corals

14. Define population and community.
Ans: Population can be defined as the total number of individuals of a species or any other class of an organism in a defined area or habitat or a group of individuals of the same species within a commnity.
Community can be defined as a naturally octurring assemblage of species living within a defined area or habitat.

15. Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage (d)Mutualism
(e) Interspecific competition
Ans: (a) Commensalism is the association between organisms of different species in which one species benefits but does not apparent harm to the other. For example, in the large intestine of human being, bacteria Escherichia coli are present which helps in digestion.
(b) Parasitism is an association in which one organism lives on or in the body of another, from which it obtains its food. For example, the parasites of humans include fleas and lice, various bacteria, protozoans and fungi.
(c) Camouflage is a high degree of similarity between an animal and its visual environment, which enables it be disguished or concealed. For example, birds with necks and heads of contrasting colours are not easily recognised by their enemies under certain conditions.
(d) Mutualism is an association between two organisms of different species in which each partner benefits. For example, the cross fertilization or pollination of plant flowers by insects (sometimes by birds) is a mutual relation of wide occurrence and great importance, because many plants are self- sterile.
(e) Inter-specific competition can be defined as an interaction occurs between different species that share some environmental resource when this is in short supply. Inter-specific competition often results in the dominance of one species over another. For example, when two species of Paramoecium,Paramoecium caudatum and P.aurelia are confined in a closed containers with fixed amount of food, out of them one species always died out.

16. With the help of suitable diagram describe the . ; logistic population growth curve.
Ans: The S-shaped growth curve is also called a logistic growth curve. It describes a situation in which (in a new environmental condition) the population density of an organism increases slowly establishing itself then increasing rapidly, approaching an exponential growth rate. Many population of micro-organisms broadly follow this basic sigmoidal pattern. For example, when a fresh culture medium is inoculated with bacteria, sigmoidal or S-shaped growth curve is observed. The S-shaped curve is generated when a population approaches the environmental’s carrying capacity. Carrying capacity is the maximum number of individuals of a population that can be supported in a given time.

The S-shaped growth form is represented by the following equation- ” dNldt = rN[K-NIK]
Where, r = intrinsic rate of natural increase N = population density at time t K = carrying capacity

17. Select the statement which explains best parasitism.
(a) One organism is benefited.
(b) Both the organisms are benefited.
(c) One organism is benefited, other is not affected.
(d) One organism is benefited, other is affected.
Ans:(d) One organism is benefited, other is affected.

18.List any three important characteristics of a population and explain.
Ans: The three important characteristics of a population are:
(a) Density: The number of individuals per unit area or volume. For example, the number of frogs per m³ of forest region.
(b) Natality or Birth rate: The birth rate is determined by the number of individuals bom to a given population during a given period of time.
(c) Mortality or Death rate: The death rate or mortality represents a decrease in a given population during a given period of time. Generally, the death of individuals in a population are expressed by specific mortality which is described as the mortality population are expressed by specific mortality which is described as the mortality for given age group.

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NCERT Solutions For Class 12 Biology Microbes in Human Welfare

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 10 Microbes in Human Welfare:

Section Name	Topic Name
10	Microbes in Human Welfare
10.1	Microbes in Household Products
10.2	Microbes in Industrial Products
10.3	Microbes in Sewage Treatment
10.4	Microbes in Production of Biogas
10.5	Microbes as Biocontrol Agents
10.6	Microbes as Biofertilisers
10.7	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Bacteria cannot be seen with the naked eyes, but these can be seen with the help of a microscope. If you have to carry a sample from your home to your biology laboratory to demonstrate the presence of microbes under a microscope, which sample would you carry and why?
Ans: Soil sample/water sample as they are the natural habitat of micro-organisms and can be directly observed.

2. Give examples to prove that microbes release, gases during metabolism.
Ans: There are lots of examples which prove, that microbes release gases during their metabolism. Some examples are as follows :

• Dough, which is used for making dosa and idli is fermented by bacteria. The puffy appearance of dough is due to production of CO₂ by fermentation process.
• Swiss cheese is characterized by having the characteristic flavour and large holes. The large holes are formed due to the amount of CO₂ released by a bacterium Propionibacterium sharmanii.

3. In which food would you find lactic acid bacteria? Mention some of their useful applications.
Ans: Milk, Curd and Cheese are coagulated product. Lactic acid bacteria (LAB) convert lactose sugar into lactic acid. They also improve the nutritional quality of curd by increasing vitamin B₁₂. Lactic acid bacteria are also found in the stomach where they check disease causing microbes.

4. Name some traditional Indian foods made of wheat, rice and Bengal gram (or their products) which involve use of microbes.
Ans: A number of dishes can be prepared through fermentation process by using microbes. Some important traditional dishes made up of wheat, rice and Bengal gram or black gram (vernacular urad) are as follows :

• Bread – It is a fermented preparation of wheat by Saccharomyces cerevisiae.
• Dosa, upma and idli – They are fermented preparation of rice and black gram (urad). The two are allowed to ferment for 3-12 hrs with Leuconostoc and Streptococcus species of bacteria.

5. In which way have microbes played a major role in controlling diseases caused by harmful bacteria?
Ans: By production of antibiotics like penicillin, tetracyclin, by production of vaccines for herpes, TB, DPT, etc.

6. Name any two species of fungus, which are used in the production of the antibiotics.
Ans: Penicillium chrysogenum, P. notatum, produce penicillin and Cephalosporium produces cephalosporins.

7. What is sewage? In which way can sewage be harmful to us?
Ans: Sewage is waste water release from household and industrial applications. It is harmful as
(i) it decreases flora mid fauna of H₂O.
(ii) contamination of H₂O/food/soil.
(iii) dissemination of pathogenic bacteria.

8. What is the key difference between primary and secondary sewage treatment?
Ans: There are three stages of sewage treatment : primary, secondary and tertiary. Primary treatment is a physical process while secondary is a biological process and tertiary is a chemical process.

9. Do you think microbes can also be used as source of energy? If yes, how?
Ans: Yes, the microbes present in activated sludge are digested anaerobically to generate a biogas i.e. by release of inflammable biogas in biogas plant, which is a source of energy.
Use of microbial culture for SCP (single cell protein).

10. Microbes can be used to decrease the use of chemical fertilizers and pesticides. Explain how this can be accomplished.
Ans: Microbes can be used to decrease the use of chemical fertilizers and pesticides. This can be accomplished by the use of biofertilizers. The main source of biofertilizers are bacteria, fungi and cyanobacteria. They can provide plant nutrients at cheaper cost when compared with the chemical fertilizers. e.g.
(i) Use of leguminous plant with Rhizobium.
(ii) Use of sulphur fixing bacteria.
(iii) Use of hydrogen fixing bacterium.

11. Three water samples namely river water, untreated sewage water and secondary effluent discharged from a sewage treatment plant were subjected to BOD test. The samples were labelled A, B and C; but the laboratory attendant did not note which was which. The BOD values of the three samples A, B and C were recorded as 20 mg/L, 8 mg/Land 400 mg/L, respectively. Which sample of the water is most polluted? Can you assign the correct label to each assuming the river water is relatively clean?
Ans: The sample with BOD value of 400 mg/h is most polluted and should be levelled as B —> untreated sewage river H₂O will be —> less BOD —> 8 mg/L – sample A.
Untreated water —> 2° effluent BOD —>River water 400 —> 20 —> 8 and so should be labelled as sample C.

12. Find out the name of the microbes from which cyclosporin A (an immuno suppressive drug) and statins (blood cholesterol lowering agents) are obtained.
Ans: Cyclosporin A (an immuno suppressive drug) is obtained from fungus Trichoderma polysporum while statins (blood cholesterol lowering agent) is obtained from yeast Monascus purpureus.

13. Find out the role of microbes in the following and discuss it with your teacher.
(a) Single cell protein (SCP)
(b) Soil
Ans: SCP – single cell protein is microbial yield/cell crop of bacterial, yeast, algae rich in protein. The protein content of microbial cell is very high. Dried cell of Pseudomonas grown on petroleum product has 69% protein and these proteins have all essential amino acids.

Soil : Microbes take part in formation and maintenance of soil. They add organic matter to freshly formed soil. The process is called humification. Some microbes act as biofertilizers and biopesticides.

14. Arrange the following in the decreasing order (most important first) of their importance, for the welfare of human society. Give reasons for your answer.Biogas, Citric acid, Penicillin and Curd.
Ans: Curd: Less important for society – as it depends on individual use and has only nutritions value.
Citric acid : Industrial use, not for dissipation in community.
Penicillin: Medicinal use of microbes, good for health of society, commercially more usable.
Biogas: Most important for community welfare as
(i) it reduces excreta, waste from community.
(ii) it produces inflammable gases, can be used as energy source.
(iii) it is a renewable source.
(iv) it has multidimensional utility.
(v) it is easily maintained and dissipated for community purpose.
So,Penicillin > Biogas > Curd > Citric acid.

15. How do biofertilizers enrich the fertility of the soil?
Ans: Biofertilizers enrich the fertility of the soil by:
(i) replenishment of lost nutrients like N2, phosphorus, iron, sulphur.
(ii) addition of required micronutrients and macronutrients.
(iii) making humus acid compost.
(iv) acting as scavanger.

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NCERT Solutions For Class 12 Biology Strategies for Enhancement in Food Production

Topics and Subtopics in NCERT Solutions for Class 12 Biology Chapter 9 Strategies for Enhancement in Food Production:

Section Name	Topic Name
9	Strategies for Enhancement in Food Production
9.1	Animal Husbandry
9.2	Plant Breeding
9.3	Single Cell Proteins
9.4	Tissue Culture
9.5	Summary

QUESTIONS FROM TEXTBOOK SOLVED

1. Explain in brief the role of animal husbandry in human welfare.
Ans: Animal husbandry deals with the caring, feeding and management of domesticated animals. It includes poultry, farming and fisheries.
These animals are very useful for human beings because
(i) they provide products which are used as food like meat, milk, eggs, honey, etc.
(ii) there are some other substances obtained from animals which are beneficial to human beings like wool, silk, leather, bees wax etc.

2. If your family owned a dairy farm, what measures would you undertake to improve the quality and quantity of milk production?
Ans: To improve the quality & quantity of milk production, one should take care of the following points:
(i) Proper feeding of the cattle with good quality of food.
(ii) Clean and hygienic environment for cattles.
(iii) Proper medication.
(iv) Veterinary supervision.
(v) Selection of good breeds having high yielding capacity combined with resistance to disease.
(vi) Quality of breed.

3. What is meant by the term ‘breed’ ? What are the objectives of animal breeding?
Ans: A group of animals related by descent and similar in most characters like general appearance, features, size, configuration etc. is called a breed.
The main objectives of animal breeding are:

• To produce high yielding varieties of animals like high milk producing cattle, more egg producing varieties of chicken, more wool bearing sheep varieties etc.
• To produce drought varieties for doing work like cattle, etc.
• To produce disease resistant varieties of the livestocks.

4. Name the methods employed in animal breeding. According to you which of the methods is best? Why?
Ans: Methods employed in animal breeding are
(i) Inbreeding
(ii) Out-breeding
(iii) Cross-breeding
(iv) Interspecific hybridization
(v) Artificial insemination
(vi) Multiple Ovulation Embryo Transfer Cross breeding is the best method as it results in the development of superior traits of both the breeds and the progeny produced are fertile and there is no inbreeding depression.

5. What is apiculture? How is it important in our lives?
Ans: Apiculture is the rearing and breeding of honeybees for the production of honey .
It is important in our live as honeybees provide honey, which is a highly nutritive substance and beeswax is used in many industries. Honeybees also pollinate flowers of some very important plants like sunflower, apple, pear.

6. Discuss the role of fishery in enhancement of food production.
Ans: Fishery is an industry which is concerned with the catching, processing or selling of fish. The role of fishery in enhancement of food production is as follows :

1. The fish flesh is an excellent source of protein. It has very little fat, carries a good amount of minerals and vitamins A and D and is rich in iodine.
2. Fish oil extracted from the liver of the sharks, sawfishes, etc., has medicinal value.
3. Shagreen, the skin of sharks and rays are used in polishing the wood and other materials.
4. The silvery bony scales of cyprimids are used in the manufacture of artificial pearls.
5. Fish glue is a sticky product obtained from the skin of cod and is used as gum.
6. Fish waste after the extraction of oil is used as fertilizer.
7. The fishing industry has brought a lot of income to the farmers in particular and the country in general because of “Blue Revolution” (fish production) in the same lines as ‘Green Revolution’ (for producing enough food for all).

7. Briefly describe various steps involved in plant breeding.
Ans: Plant breeding is a purposeful manipulation of plant species in order to create desired plant types that are better suited for cultivation, give better yields and are disease resistant. The given flow chart shows various steps involved in plant breeding.

8. Explain what is meant by biofortification.
Ans: Enhancement of nutritional quality of a crop by improving the content and quality of protein, fats, vitamins, minerals and micronutrient is called biofortification. It helps to improve public health.

9. Which part of the plant is best suited for making virus-free plants and why?
Ans: The apical and axillary meristems of plants are the best parts of the plant to make virus-free plants. This is because rate of division of meristematic cell is higher than rate of multiplication of virus and viruses are unable to invade newly formed meristematic cells. Hence, meristematic cells are free of virus although the whole plant is infected with virus. With the use of meristem, a healthy plant can be recovered from the diseased plant through micropropagation method.

10. What is the major advantage of producing plants by micro propagation?
Ans: It is faster method of producing a large number of plants. Plants formed by micro propagation are identical.

11. Find out the various components of the medium 12.used for propagation of an explant in vitro are ?
Ans: The various components of the medium used for propagation of an explant in vitro are
-Sucrose (source of energy & carbon)
-Inorganic salts
-Vitamins
-Growth regulators (auxins and cytokinins)

12. Name any five hybrid varieties of crop plants which have been developed in India.
Ans: Sonalika (wheat)
Himgiri (wheat)
Pusa Swamim (mustard)
PusaSem2 (bean)
Pusa Sawani (lady’s finger)

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