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NCERT Exemplar · Class 9 Science Improvement in Food Resources

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Long Answer Questions 36–45 (part 5 of 6)

  1. Exercise 36

    Discuss the role of hybridisation in crop improvement.

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    NCERT’s answer
    Hybridisation refers to crossing between genetically dissimilar plants. It may be inter varietel, inter specific and inter generic. Two crops of good characters (desired character) are selected and crossed to obtain a new crop having desired characters of parental crops. This method of hybridisation improves crops with respect to yield, disease resistance, pest resistance etc.
    Hybridisation crosses genetically different plants to combine their good traits in one offspring. \[\text{Parent A (disease-resistant)} \times \text{Parent B (high-yielding)} \rightarrow \text{Hybrid (both traits)} \] Crosses may be intervarietal (between two varieties of the same species), interspecific (between two species of the same genus), or intergeneric (between two different genera). The hybrid combines the parents' good qualities — higher yield, better grain quality, disease/pest resistance and wider climatic adaptability — and, after further selection, becomes an improved variety.Answer: Crossing two genetically different, desirable parents (intervarietal, interspecific or intergeneric) produces a hybrid combining both parents' good traits, e.g. yield with disease resistance.

  2. Exercise 37

    Define
    (i)
    Vermicompost
    (ii)
    Green manure
    (iii)
    Bio fertilizer

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    NCERT’s answer
    (a)
    Vermicompost — Compost is a kind of manure which is rich in organic matter and nutrients. The compost prepared by using earthworms to hasten the process of decomposition of plants and animals refuse is called as Vermicompost. (b) Green manure — The manure which is prepared by decomposing green plants in field itself is called green manure. For example — sun hemp is grown in fields, mulched by ploughing and allowed to decompose in field for the preparation of green manure. (c) Bio fertilizer— Living organisms which are used as fertilizer to supply the nutrients to plants, are called as biofertilizers. For example, blue green algae, which fix nitrogen in soil, rice fields, are called as biofertilizer.
    (i)
    Vermicompost — organic manure made by culturing earthworms on biodegradable kitchen and farm waste; the worms convert it into a nutrient-rich, crumbly compost.
    (ii)
    Green manure — manure made by growing a quick green crop, such as sunhemp or guar, in the field and ploughing it under before it flowers, adding organic matter and nitrogen straight into the soil.
    (iii)
    Bio-fertilizer — living organisms, such as the bacteria Rhizobium and Azotobacter or blue-green algae, that fix atmospheric nitrogen and enrich the soil when added to seed or soil.
    Answer: Vermicompost — earthworm-processed waste; green manure — a green crop ploughed into the soil; bio-fertilizer — nitrogen-fixing organisms added to seed/soil.

  3. Exercise 38

    Discuss various methods for weed control.

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    NCERT’s answer
    Various modes of weed control are (a) mechanical removal (b) proper seed bed preparation to avoid the weed growth (c) timely sowing of crop to avoid the growth of weed. (d) intercropping and crop rotation also help in weed control.
    Mechanical/cultural: deep ploughing before sowing exposes weed roots to the sun; proper seed-bed preparation, hand-pulling, hoeing, timely sowing, proper spacing, intercropping and crop rotation deny weeds a foothold.Chemical: weedicides such as $\displaystyle 2,4$-D are sprayed on the field, timed before the weeds flower and set seed, so they do not reseed the field before dying; the person spraying must wear protective clothing and a mask, since weedicides are poisonous to humans too.Answer: Weeds are removed mechanically (ploughing, hand-weeding), culturally (timely sowing, intercropping, rotation) or chemically (weedicide such as $\displaystyle 2,4$-D, sprayed before the weeds seed, with protective clothing for the sprayer).

  4. Exercise 39

    Differentiate between the following
    (i)
    Capture fishery and Culture fishery
    (ii)
    Mixed cropping and Inter cropping
    (iii)
    Bee keeping and Poultry farming

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    NCERT’s answer
    (a)
    Capture fishery is the method of obtaining fish from natural resources while culture fishery is the method of obtaining fish by fish farming. (b) Mixed cropping is growing two or more crops simultaneously on the same piece of land; while intercropping is growing two or more crops simultaneously on the same field in a definite pattern. i.e., in different rows. (c) Bee keeping is the practice to rear the honey bee for obtaining honey; while poultry farming is the practice to raise the domestic fowl for egg and meat production.
    (i)
    Capture fishery: fish caught from natural waters — sea, rivers, lakes — with uncontrolled breeding. Culture fishery: fish reared in a managed pond with controlled breeding and feeding, for a higher, assured yield.
    (ii)
    Mixed cropping sows two crops together, seeds mixed, no fixed row pattern — insurance against total crop failure. Inter-cropping plants them in a fixed pattern of alternating rows, raising yield per unit area.
    (iii)
    Bee keeping (apiculture): honeybee colonies kept in boxes near flowering crops, for honey and wax. Poultry farming: birds like fowl reared in housing on controlled feed, for eggs and meat.
    Answer: wild-caught vs pond-reared fish; no-pattern risk-cover vs fixed-row higher yield; honey/wax vs eggs/meat.

  5. Exercise 40

    Give the merits and demerits of fish culture?

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    NCERT’s answer
    Hint— Demerits (i) threat to bio-diversity (ii) only economically important and valued fishes will be cultured. Merits (i) large amount of desired fishes can be obtained in small area (ii) improvement can be done.
    Merits: yield is higher and steadier than capture from open water; breeding and disease control are managed; composite culture stocks five-six compatible species (surface, middle-water, bottom and weed feeders) in one pond, using its full capacity; selected broodstock and hybrids grow faster and stay healthier.Demerits: good seed is often scarce; it threatens biodiversity, since stocking exotic or selected species can displace indigenous ones; and usually only economically valued species are cultured, so others are neglected.Answer: Merits — higher, managed yield; full pond use via composite culture; improved broodstock/hybrids. Demerits — scarce good seed; threat to biodiversity; only economically valued species cultured.

  6. Exercise 41

    What do you understand by composite fish culture?

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    NCERT’s answer
    Composite fish culture is the method to culture five or six species, both indegenous and exotic, together in a single fish pond. These species are selected so that they do not compete for food among themselves having different types of food habits. As a result food available in all the parts of the pond is used. For example— Catlas are surface feeders, Rohu is middle zone feeder and Mrigals and common carps are bottom feeders.
    Composite fish culture stocks five or six compatible indigenous and exotic fish species together in one pond so the food at every level is used and total yield rises. Catla feeds at the surface, Rohu in the middle zone, Mrigal and Common carp scavenge the bottom, and Grass carp grazes the weeds — no two species compete for the same food or space, so all can be stocked together at high density. Answer: Composite fish culture stocks five or six compatible species (Catla, Rohu, Mrigal, Common carp, Grass carp) that feed in different zones of one pond, so all the food is used and yield is maximised.

  7. Exercise 42

    Why bee keeping should be done in good pasturage?

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    NCERT’s answer
    Because good pasturage provides more quantity and quality of nectar for honey to honey bees.
    \[\text{good pasturage} \Rightarrow \text{abundant, continuous nectar and pollen} \Rightarrow \text{more honey, of better quality} \] Nectar is the raw material bees convert into honey, while pollen is their protein food for the colony and brood; a site with plentiful bloom nearby keeps the colony well fed and productive through the season.Answer: Good pasturage gives bees abundant nectar, the raw material for honey, and pollen to feed the colony and brood, so bee keeping sited there raises both the honey yield and its quality.

  8. Exercise 43

    Write the modes by which insects affect the crop yield.

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    NCERT’s answer
    Hint—Cutting plant parts, sucking cell sap, borers.
    Insects damage crops in three modes:
    cutting — they cut the root, stem and leaf
    boring — they bore into the stem and fruit, destroying tissue from within
    sap-sucking — they pierce soft tissue and withdraw cell sap, lowering the plant's vigour and stunting growth
    Answer: Insects lower yield by (i) cutting roots, stems and leaves, (ii) boring into stems and fruits, and (iii) sucking cell sap, which weakens plant vigour and growth.

  9. Exercise 44

    Discuss why pesticides are used in very accurate concentration and in very appropriate manner?

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    NCERT’s answer
    Pesticides are used in very accurate concentration and in a very appropriate manner, because if used in excess it (a) harms the soil and causes loss of fertility (b) checks the replenishment of organic matter (c) kills the micro organism of soil (d) causes air, water and soil pollution.
    \[\text{concentration too low} \Rightarrow \text{pest survives, resistance builds} \] \[\text{concentration too high} \Rightarrow \text{toxic residue in crop, soil and water} \] \[\text{residue in soil}\uparrow \Rightarrow \text{soil micro-organisms killed} \Rightarrow \text{organic-matter replenishment blocked} \Rightarrow \text{soil fertility}\downarrow \] The excess residue also enters the food chain and biomagnifies up trophic levels, harming non-target organisms — including humans who eat the crop or drink the water — and kills useful insects such as pollinators.Answer: An accurate, judiciously applied concentration controls the target pest while avoiding resistance, toxic residues, biomagnification, loss of soil fertility and harm to non-target organisms.

  10. Exercise 45

    Name two types of animal feed and write their functions.

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    NCERT’s answer
    Hint— (i) Roughage is largely fibre. (ii) Concentrates are rich in proteins and nutrients.
    Animal feed is of two types:
    roughage — bulky, fibre-rich, low in other nutrients, e.g. green fodder, hay, straw, silage; keeps the rumen working and the digestive tract healthy
    concentrate — low in fibre, nutrient-dense, e.g. grains, oil cakes, bran; supplies the protein, minerals and energy that roughage alone cannot
    Answer: Roughage supplies bulk and fibre for digestion; concentrate supplies the protein, minerals and energy needed for growth and milk production.