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NCERT Solutions · Class 12 Biology Biotechnology and its Applications

13 exercises · 13 still being checked

Exercises 10.1–10.13

  1. Exercise 10.1

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

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    The meristem — the apical and axillary meristem — is best suited.
    Even when the plant is infected with a virus, the meristem is free of the virus.
    So the meristem is removed and grown in vitro in a sterile nutrient medium, and the whole plant regenerated from it is virus-free.
    Scientists have obtained virus-free banana, sugarcane and potato by culturing meristems this way.

  2. Exercise 10.2

    What is the major advantage of producing plants by micropropagation?

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    The major advantage is that thousands of plants can be produced in a very short duration, which conventional propagation cannot achieve.
    Every plant so raised is a somaclone — genetically identical to the parent plant — so a desirable variety is multiplied without any change in its characters.
    Any part of the plant can be used as the explant, because plant cells are totipotent.
    It is already used on a commercial scale for important food plants such as tomato, banana and apple.

  3. Exercise 10.3

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

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    The nutrient medium in which the explant is grown must provide:
    A carbon source, such as sucrose.
    Inorganic salts.
    Vitamins.
    Amino acids.
    Growth regulators — auxins, cytokinins, etc.
    The explant is grown in this medium in a test tube under sterile conditions; from it a whole plant regenerates, because of totipotency.

  4. Exercise 10.4

    Crystals of Bt toxin produced by some bacteria do not kill the bacteria themselves because -
    (a)
    bacteria are resistant to the toxin
    (b)
    toxin is immature;
    (c)
    toxin is inactive;
    (d)
    bacteria encloses toxin in a special sac.

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    (c) toxin is inactive.
    Inside Bacillus thuringiensis the Bt toxin exists as an inactive protoxin, packed into protein crystals formed during a particular phase of the bacterium's growth, so it cannot harm the bacterium itself.
    It is converted to the active form only after an insect ingests it: the alkaline pH of the insect gut solubilises the crystals and activates the toxin.
    The activated toxin binds the surface of the midgut epithelial cells and creates pores, so the cells swell and lyse and the insect dies.

  5. Exercise 10.5

    What are transgenic bacteria? Illustrate using any one example.

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    Transgenic bacteria are bacteria whose DNA has been manipulated so that they possess and express an extra (foreign) gene — i.e., genetically modified organisms.
    Example: E. coli made to produce human insulin.
    In $\displaystyle 1983$ the American company Eli Lilly prepared two DNA sequences corresponding to chains A and B of human insulin and introduced them into plasmids of E. coli.
    The two chains were produced separately, extracted, and then combined by creating disulphide bonds to form human insulin.
    The benefit: this insulin is identical to the human hormone, so it avoids the allergy and other reactions that insulin extracted from the pancreas of slaughtered cattle and pigs caused in some patients.

  6. Exercise 10.6

    Compare and contrast the advantages and disadvantages of production of genetically modified crops.

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    Advantages
    Crops are made more tolerant to abiotic stresses — cold, drought, salt and heat.
    Reliance on chemical pesticides is reduced by pest-resistant crops such as Bt cotton, which carry their own bio-pesticide.
    Post-harvest losses are reduced.
    The efficiency of mineral usage by plants is increased, which prevents early exhaustion of soil fertility.
    The nutritional value of food is enhanced, e.g., golden rice, i.e., Vitamin 'A' enriched rice.
    Tailor-made plants supply industries with alternative resources in the form of starches, fuels and pharmaceuticals.
    Disadvantages
    Genetic modification can have unpredictable results when such organisms are introduced into an ecosystem, so the release of GM organisms cannot go on without regulation — in India it needs clearance from the GEAC (Genetic Engineering Approval Committee).
    The manipulation of living organisms raises serious ethical questions about the morality of such activity.
    It has created patent problems and biopiracy: companies obtain patents on products and technologies that use genetic material long identified and developed by farmers and indigenous people, as with the $\displaystyle 1997$ US patent on Basmati rice.

  7. Exercise 10.7

    What are Cry proteins? Name an organism that produce it. How has man exploited this protein to his benefit?

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    Cry proteins are the toxic insecticidal proteins coded by the genes named cry — they are the Bt toxin.
    Organism: *Bacillus thuringiensis* (Bt), which forms protein crystals containing this toxin during a particular phase of its growth.
    They exist as inactive protoxins and are activated by the alkaline pH of an insect's gut, after which they bind the midgut epithelial cells, create pores and lyse them, killing the insect.
    How man has exploited it: specific cry genes were isolated from B. thuringiensis and incorporated into crop plants, so the plant itself makes the toxin and resists insects without any insecticide — in effect a bio-pesticide. Examples are Bt cotton, Bt corn, rice, tomato, potato and soyabean.
    The gene chosen must match the pest, as most Bt toxins are insect-group specific: cryIAc and cryIIAb control the cotton bollworms, and cryIAb controls the corn borer.

  8. Exercise 10.8

    What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.

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    Gene therapy is a collection of methods that allows correction of a gene defect diagnosed in a child or embryo: genes are inserted into a person's cells and tissues so that a normal gene delivered into the individual takes over the function of, and compensates for, the non-functional gene.
    The first clinical gene therapy was given in $\displaystyle 1990$ to a $\displaystyle 4$-year-old girl with adenosine deaminase (ADA) deficiency.
    The ADA example
    ADA deficiency is caused by deletion of the gene for adenosine deaminase, an enzyme crucial for the immune system to function.
    Existing treatments are not complete cures — bone marrow transplantation cures some children, and in others functional ADA is supplied by injection (enzyme replacement therapy).
    Step $\displaystyle 1$: lymphocytes from the patient's blood are grown in a culture outside the body.
    Step $\displaystyle 2$: a functional ADA cDNA is introduced into these lymphocytes using a retroviral vector.
    Step $\displaystyle 3$: the engineered lymphocytes are returned to the patient.
    Because these cells are not immortal, the patient needs periodic infusion of such genetically engineered lymphocytes.
    A permanent cure would be possible if the gene isolated from marrow cells producing ADA were introduced into cells at early embryonic stages.

  9. Exercise 10.9

    Digrammatically represent the experimental steps in cloning and expressing an human gene (say the gene for growth hormone) into a bacterium like E. coli ?

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    Draw it as a Y-shaped flow chart: two short parallel columns at the top — the gene on the left, the vector on the right — that converge on the ligation box, and one vertical column of boxes running down from there to the finished product. Every bullet below is one labelled box, joined to the next by a downward arrow.
    Left arm — the gene
    1. A human cell with its nucleus, and an arrow from it to a short straight DNA segment labelled human growth hormone gene — the gene of interest.
    2. Directly below it, a pair of scissors labelled restriction endonuclease cutting that segment; draw the cut ends staggered, as sticky ends.
    Right arm — the vector
    3. A circular plasmid drawn as a ring, carrying three labels on the ring: ori (origin of replication), selectable marker, and restriction site.
    4. Directly below it, the same scissors opening the ring into a linear molecule with matching sticky ends. Write same enzyme cuts both between the two pairs of scissors, so the two arms are visibly linked.
    Stem — from ligation downwards
    5. One arrow from the foot of each arm; both converge on a single box labelled DNA ligase. Below that box draw its product: a ring with the gene drawn in as an inserted segment, labelled recombinant DNA.
    6. Arrow down to a rod-shaped bacterium labelled *E. coli*; label the arrow transformation.
    7. Arrow down to an agar plate bearing several colonies with a few of them shaded, labelled transformed cells picked out using the selectable marker.
    8. Arrow down to a bioreactor — a stirred tank with an impeller, an air inlet and an outlet — labelled foreign gene expressed; growth hormone made.
    9. Arrow down to a box labelled downstream processing (separation and purification), and from it to a final vial labelled human growth hormone, with formulation with preservatives, quality control testing, clinical trials written alongside.
    Point every arrowhead downwards, so the chart reads at a glance: gene and vector cut in parallel → ligate → transform → select → culture → purify → product.

  10. Exercise 10.10

    Can you suggest a method to remove oil (hydrocarbon) from seeds based on your understanding of rDNA technology and chemistry of oil?

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    Suggested method: silence the gene for the oil-forming enzyme in the seed, using RNA interference (RNAi) — so the seed never makes the oil, rather than trying to wash it out afterwards.
    The chapter's nematode experiment gives the recipe: using Agrobacterium vectors, introduce into the plant a construct designed so that the host cells produce both sense and anti-sense RNA.
    The two RNAs, being complementary, pair to form double-stranded RNA (dsRNA), which initiates RNAi and silences the target mRNA by preventing its translation.
    Choose as the target the mRNA of the enzyme that synthesises oil in the developing seed; with that enzyme silenced, the seed develops without laying down oil.
    The chemistry is why removal is the harder route: oil is non-polar and does not dissolve in water, so it can only be pressed out or taken up in a non-polar solvent — blocking its synthesis genetically is the cleaner solution.

  11. Exercise 10.11

    Find out from internet what is golden rice.

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    NCERT publishes no answers for this textbook, so there is nothing in the book to check this working against. It has also not yet been read through by hand.

    Golden rice is Vitamin 'A' enriched rice — the chapter's own example of a genetically modified crop created to enhance the nutritional value of food.
    It appears in the chapter's list of what genetic modification has achieved in plants, alongside tolerance to abiotic stresses, pest resistance, reduced post-harvest losses and better mineral-use efficiency.
    What the internet search is meant to add (beyond this chapter): the rice is engineered to accumulate β-carotene — the orange provitamin-A pigment that gives the grain its golden colour — in the edible endosperm, so that eating the rice supplies vitamin A in regions where deficiency is common.

  12. Exercise 10.12

    Does our blood have proteases and nucleases?

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    Yes — blood does carry proteases, and nuclease activity is present in small amounts.
    Proteases: blood clotting and the dissolution of clots are themselves cascades of protein-splitting enzymes acting on plasma proteins, so proteases circulate in plasma, mostly as inactive precursors that are switched on when required.
    Nucleases: traces of DNase and RNase activity occur in serum, which is why free DNA and RNA do not persist in circulation.
    Why the chapter makes you ask this: every protein therapeutic in the chapter is delivered by injection — insulin taken at regular intervals, functional ADA given by injection — and the chapter asks you to think about whether insulin can be given orally. Protein-digesting enzymes are the reason a protein drug cannot simply be swallowed, and the reason an injected protein does not survive indefinitely in the body either.

  13. Exercise 10.13

    Consult internet and find out how to make orally active protein pharmaceutical. What is the major problem to be encountered? Diversity is not only a characteristic of living organisms but

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    The major problem is digestion: a protein taken by mouth is broken down by the proteases of the stomach and small intestine into peptides and amino acids before it can act, and even an undigested protein molecule is too large to be absorbed intact across the gut wall.
    What the chapter establishes: every protein therapeutic in it is given by injection — insulin is taken at regular time intervals, and functional ADA is given to the patient by injection — and the chapter explicitly asks you to think about whether insulin can be administered orally, and why not.
    Lines of attack a search will turn up (none of these are in the chapter): an enteric or polymer coating, or encapsulation, so the protein passes the stomach unharmed; co-delivery with protease inhibitors; absorption enhancers that help the protein cross the intestinal lining; or redesigning the molecule itself so that it resists digestion.