NCERT Solutions Class 12 Biology Chapter 9

Q.1 Explain in brief the role of animal husbandry in human welfare.

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Animal husbandry involves breeding and taking care of domestic animals by using scientific principles. Animal husbandry deals with the care and breeding of livestock that is useful to humans like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats, etc. It also includes poultry farming and fisheries.

Animal husbandry plays a useful role in human welfare by providing us with improved quality of milk, meat, eggs, wool, silk, honey and many other useful products having economic value. Also, rearing of animals generates employment for many.

Q.2 If your family owned a dairy farm, what measures would you undertake to improve the quality and quantity of milk production?

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Milk production, in terms of both quality and quantity, depends on various aspects ranging from the breed of the animal to their keeping and handling.

Following measures can be undertaken to improve the quality and quantity of milk production:

1. Good breed of the animal: A good breed will have greater milk yielding potential and resistance to diseases.
2. Providing suitable environmental condition: Adequate ventilation, suitable temperature, sufficient light, water, air and well-drained hygienic housing accommodation should be provided.
3. Food or fodder should be balanced, nutritious and adequate in terms of quantity.
4. Stringent cleanliness and hygiene of both the animal and the caretaker are essential while milking and storage of milk.
5. If any processes are mechanised, they should undergo regular inspection and quality control.
6. Vaccination and regular health checks by a veterinary doctor are mandatory.

Q.3 What is meant by the term ‘breed’? What are the objectives of animal breeding?

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A group of animals related by descent and similar in most characters like general appearance, features, size, configuration, etc. are said to belong to a breed. The objectives of breeding are as follows:

1. Selecting animals with a higher and superior yield of produce (like egg, meat, milk, or wool).
2. To increase the resistance of the livestock to diseases, epidemics and making them suitable to local environmental conditions (e.g. availability of less water).

Some examples of breeds of cows are:

• Ongole breed is indigenous to India, produces 3-12 litres of milk every day during lactation period. The fat content in the milk is over 5%.
• Holstein breed of cow produces 24-28 litres of milk per day.

Q.4 Name the methods employed in animal breeding. According to you, which of the methods is best? Why?

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Animal breeding is a technique whereby two closely related animals are mated to yield progeny having desirable characters of both the parents. Methods of animal breeding are:

Natural breeding: It includes the following:

1. Inbreeding – Mating of more closely related individuals within the same breed for 4-6 generations.
2. Outbreeding – It is breeding between unrelated animals. This is of the following types:

Cross-breeding: In this method, superior males of one breed are mated with superior females of another breed. Cross-breeding allows the desirable qualities of two different breeds to be combined.

Interspecific breeding: In this method, male and female animals of two different species are mated. In some cases, the progeny may combine desirable features of both the parents and may be of considerable economic value, e.g., the mule which is a cross between a donkey and a horse.

Out-crossing: This is the practice of mating of animals within the same breed, but having no common ancestors on either side of their pedigree up to 4-6 generations.

Artificial/ controlled breeding employs the following techniques:

1. Multiple Ovulation Embryo Transfer Technology (MOET): In this method, a cow is administered hormones, with FSH-like activity, to induce follicular maturation and superovulation so that instead of one egg, which they normally yield per cycle they produce 6-8 eggs.
2. Artificial insemination –The superovulated cows are artificially inseminated with the sperms of a male having desired traits. The embryos at an 8-32 day stage are removed from the genetic mother and transferred into surrogate mothers (that may be of lower quality). In this way, more progeny of the desired cross can be produced. Also, the genetic mother can be put through another cycle of superovulation.
3. Sex determination – The sex of the embryos can be determined in utero at about 50 days of gestation. The normal gestation for Holstein-Friesian cattle is about 280 days, so this early determination of sex saves many days and allows the breeding program to be adjusted.

The controlled breeding methodology is much more accurate in terms of the desired crosses and the number of progeny of the desired parents that can be produced in one gestation period.

Q.5 What is apiculture? How is it important in our lives?

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Apiculture or bee-keeping is the maintenance of hives of honeybees for the production of honey. The first records of bee keeping go back upto 15,000 years. Today, this cottage industry has been adapted for high yield, easy harvest of honey and methods that do not involve the killing of huge number of bees as is done traditionally. Honey has many uses ranging from being used as a nutritive food, in the food industry to being used as a medicine. Bee-keeping is also a source of natural substances other than honey such as bees wax (used in cosmetics), propolis (traditional medicine) and royal jelly (traditional medicine, cosmetics, and dietary supplements). Apiculture also serves as a source for earning livelihood and can be carried out at low setup and low labour costs too.

Q.6 Discuss the role of fishery in enhancement of food production.

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Fishery is an industry devoted to the catching, processing or selling of fish, shellfish or other aquatic animals. A large number of our population is dependent on fish, fish products and other aquatic animals such as prawn, crab, lobster, edible oyster, etc., for food. Fish and other aquatic animals make for nutritious and high protein content food.

Blue revolution is being implemented in India which has helped to increase fish production by 10 fold in India since independence in 1947. This has happened because of different techniques like pisciculture (the breeding, rearing, and transplantation of fish by artificial means) and aquaculture (farming of aquatic organisms such as fish, crustaceans, molluscs and aquatic plants) which have helped to increase the production of aquatic animals and plants, both fresh-water and marine.

Q.7 Briefly describe various steps involved in plant breeding.

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Plant breeding is a process that involves crossing or hybridization of pure lines followed by artificial selection to produce plants with desirable traits of higher yield, nutritive value and resistance to diseases. Green revolution in India came about so that, low yielding crop varieties could be replaced with varieties having desired traits such as high yield, disease resistance, drought resistance which lead to increased per hectare yields.

Classical plant breeding involves:

Collection of variability: The first step to a plant breeding program involves the collection of the genetic varieties available for that plant, which could be the wild type, existing hybrid varieties, and relatives of that plant. The entire collection (of plants/seeds) having all the diverse alleles for all the genes in a given crop is called germplasm collection.

Evaluation and selection of parents: The parents with the desired characters are selected for breeding. The parents are self crossed to get purebred lines, if possible, and are evaluated for the desired character before hybridization.

Cross hybridisation among the selected parents: The selected parents are cross-hybridised by the pollinating stigma of one parent with the pollen of the other, which is a tedious process.

Selection and testing of superior recombinants: Out of the numerous progeny from the cross, the plant that has both the desired characters of the parents is selected. This requires careful assessment and evaluation of the traits.

Inbreeding: The selected recombinants are put through a series of back crosses to yield purebred homozygous line. This confirms that the traits are inherited together, are stable and do not segregate.

Testing, release and commercialisation of new cultivars: The selected hybrids are tested for yields and other agronomic traits such as disease resistance. They are first evaluated by growing in research fields, then in certain designated farmer fields, in different regions of the country, along with the best cultivar of that region for reference. After a careful evaluation, the cultivar is released for commercialisation.

While the above method for plant breeding is an age-old method which has been practiced by our ancestors, today genetic engineering and molecular biology techniques are being used for creating different varieties of plants in a more targeted way. Genetically modified plants (GM plants) of different species are under cultivation today although some countries including India have been very conservative about GM plants. BT-brinjal is the only GM plant which has been approved for cultivation in India and has seen a slew of controversy in the past years.

Q.8 Explain what is meant by biofortification.

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Biofortification is enhancement of nutritional value of a crop by selective breeding or genetic engineering. It involves breeding crops with higher levels of vitamins, mineral, protein or fat content. Biofortification is seen as a technique to provide nutritious food to the poor in the developing countries who do not have access or the means to eat a variety of healthy or fortified food.

Example: Golden rice is a variety of Oryza sativa rice produced through genetic engineering to biosynthesise beta-carotene, a precursor of vitamin A, in the edible parts of rice. The research was conducted with the goal of producing a fortified food to be grown and consumed in areas with a shortage of dietary vitamin A, the deficiency of which is estimated to kill hundreds of thousand children under the age of 5 every year. But being a genetically modified crop plant, the golden rice has faced a lot of opposition from the environmental groups and has not yet been commercialised on a planned scale.

Q.9 Which part of the plant is best suited for making virus-free plants and why?

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The plant meristems are generally virus-free or carry a very low concentration of the virus. The reasons attributed to the absence of virus from the meristems are as follows:

1. Absence of vascular system (through which the viruses travel) from the meristem.
2. High auxin content in the shoot tip may prevent the growth of the virus.
3. High metabolic activity of the rapidly dividing apical cells prevents the propagation of the virus.

Hence, one can remove the meristem and grow it in vitro to obtain virus-free plants. Scientists have succeeded in culturing meristems of banana, sugarcane, potato, etc.

The cells of the shoot and root apical meristems (SAM and RAM) divide rapidly and are considered to be indeterminate, in that they do not possess any defined end fate. The meristematic cells are frequently compared to the stem cells in animals, which have analogous behaviour and function. Under appropriate conditions, each shoot meristem can develop into a completely new plant or clone.

Q.10 What is the major advantage of producing plants by micropropagation?

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Micropropagation is the practice of rapidly multiplying stock plant material to produce a large number of progeny plants, using modern plant tissue culture methods. Each of these plants will be genetically identical to the original plant from which they were grown, i.e., they are somaclones. Many important food plants like tomato, banana, apple, etc., have been produced on a commercial scale using this method.

Advantages of micropropagation:

1. Allows propagation of a large number of plants that are clones of each other. This is especially useful when we want to retain a trait which may otherwise get segregated during meiosis in a plant.
2. Micropropagation can produce disease-free plants as they are grown in controlled environments. This method can help recover healthy plants from diseased plants. This can be done by excising disease-free areas like the meristem from the infected plant which can be micropropagated in vitro.
3. Allows propagation of plants that do not produce seeds or have only very few seeds, or cannot reproduce vegetatively, or have seeds that cannot be stored.

Q.11 Find out what the various components of the medium used for propagation of an explant in vitro are?

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The plant tissue culture medium is an artificial nutrient supplement of organic and inorganic nutrients used for cultivation of an explant. The culture media used for the in vitro cultivation of the plant cells are composed of the following basic components:

1. Essential elements supplied as a complex mixture of salts
2. Organic supplements providing vitamins and amino acids
3. A source of carbon which is usually supplied as sucrose
4. Hormones such as auxins and gibberellins
5. A gelling agent such as agar

Q.12 Name any five hybrid varieties of crop plants which have been developed in India.

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