CBSE Class 12 Biology Biotechnology and Its Applications Worksheet Set C

Very Short Answer Questions

Question: Name two genetically modified hormones.
Answer. Insulin and human growth hormones.

Question: Name a molecular diagnostic technique to detect the presence of a pathogen in its early stage of infection. 
Answer. ELISA (Enzyme Linked Immunosorbent Assay)

Question: State the role of transposons in silencing of mRNA in eukaryotic cells. 
Answer. Transposons or mobile genetic elements in viruses are the sources of the complementary dsRNA,which in turn bind to specific mRNA and cause RNA interference of the parasite.

Question: A boy has been diagnosed with ADA deficiency. Suggest any one possible treatment.
Answer. Bone marrow transplant/enzyme replacement therapy/gene therapy.

Question: For which variety of Indian rice, patent was filed by a USA Company?
Answer. Indian Basmati was crossed with semi-dwarf variety and was claimed as a new variety for which the patent was filed by a USA company.

Question: 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.
Answer. (c) toxin is inactive.

Question: PCR requires very high temperature conditions where most of the enzymes get denatured.
How was this problem resolved in a PCR? 
Answer. This problem was resolved by the use of a thermostable DNA polymerase, Taq polymerase derived from Thermus aquaticus which remains active during the high temperature and induces denaturation of double stranded DNA.

Question: Write the two uses of PCR technique in diagnosis.
Answer. Two uses of PCR technique:
(i) It is used to detect HIV in suspected AIDS patients.
(ii) It is used to detect mutations in gene, in suspected cancer patients.

Short Answer Questions

Question: What is gene therapy? Illustrate using the example of adenosine deaminase (ADA) deficiency.
Answer. Gene therapy is a method which corrects or replaces the defective genes. In 1900, first clinical gene therapy was given to a 4-year old girl with adenosine deaminase (ADA) deficiency. This enzyme plays an important role in functioning of immune system. This disorder is caused due to the deletion of the gene for adenosine deaminase. In gene therapy, lymphocytes from the blood of the patient are grown in a culture outside the body. A functional ADA cDNA (using a retroviral vector) is then introduced into these lymphocytes, which are returned to the patients. 
However, as these cells are not immortal, hence the patient requires periodic infusion of such genetically engineered lymphocytes.

Question: Gene therapy is an attempt to correct a genetic defect by providing a normal gene into the individual. By this the normal function can be restored. Alternate method would be to provide the gene product (protein/enzyme) known as enzyme replacement therapy, which would also restore the function. Which in your opinion is a better option? Give reason for your answer.
Answer. Gene therapy would be a better option because it has the potential to completely cure the patient.
It is because the correct gene once introduced in the patient, can continue to produce the correct protein enzyme. Enzyme therapy does not offer permanent cure as it needs to be given to the patient on regular basis. It is also more expensive.

Question: Why are yeasts used extensively for functional expression of eukaryotic genes? 
Answer. Yeasts are simplest unicellular eukaryotic organisms and like bacteria they are genetically well characterised, easy to grow and manipulate. They can be readily cultured in small culture vessels as well as in large-scale bioreactors.

Question: PCR is a useful tool for early diagnosis of an infectious disease. Comment. 
Answer. PCR is a very sensitive technique which enables the specific amplification of desired DNA from a limited amount of DNA template. Hence, it can detect the presence of an infectious organism in the infected patient at an early stage of infection (even before the infectious organism has multiplied to large number).

Question: (a) Tobacco plants are damaged severely when infested with Meloidogyne incognita. Name and explain the strategy that is adopted to stop this infestation.
(b) Name the vector used for introducing the nematode specific gene in tobacco plant.
Answer. (a) Gene expression can be controlled by using RNA molecule and this technology is called RNA interference or RNAi or gene silencing. During this process nematode specific gene
is introduced into host plant (using Agrobacterium) which produces dsRNA. This silences specific mRNA of the nematode and parasite dies.
(b) Agrobacterium tumifaciens.

Question: ELISA technique is based on the principles of antigen and antibody interaction. Can this technique be used in the molecular diagnosis of a genetic disorder, such as phenylketonuria?
Answer. Yes. One can use antibody against the enzyme (that is responsible for the metabolism of phenylalanine) to develop ELISA-based diagnostic technique. The patient in which the enzyme protein is absent would give negative result in ELISA when compared to normal individual.

Question: (a) Mention the cause and the body system affected by ADA deficiency in humans.
(b) Name the vector used for transferring ADA-DNA into the recipient cells in humans. Name the recipient cells.
Answer. (a) The cause is the defective gene not producing ADA. The immune system is affected.
(b) A retroviral vector is used, recipient cells are lymphocytes.

Question: How has recombinant technology helped in large scale production of vaccines? Explain giving one example. 
Answer. Production of insulin by rDNA techniques was achieved by an American company, Eli Lilly, in 1983. It prepared two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of E. coli for production. The A and B chains produced were separated, extracted and combined by creating disulfide bonds to form human insulin.

Question: What is Biopiracy? State the initiative taken by the Indian Parliament towards it.
Answer. Biopiracy is the use of bioresources by organisations without proper authorisation from the countries and people concerned without compensatory payment.
The government has cleared patent terms, emergency provisions and research and development initiative.

Question: Compare and contrast the advantages and disadvantages of production of genetically modified crops.
Answer. Advantages of genetically modified crops:
- Reduces the use of chemical fertilisers and pesticides which cause pollution (air, water and soil).
- Production of new resistant varieties against pathogen, droughts, salinity, etc.
- Provides raw materials to industries like pharmaceuticals.
- Genetically modified crops have enhanced nutritional quality and yield.
- These crops grow fast and produce high yield through modifications.
Disadvantages of genetically modified crops:
- Proteins produced by GM organisms might cause allergy and other reactions.
- Resistance characters might develop in intestinal bacteria against antibiotics.
- Resistant genes transferred by pollen to the weeds may also become resistant to pests.

Long Answer Questions

Question: Explain the synthesis of genetically engineered human insulin.
Answer. Genetically engineered insulin
- Insulin contains two short polypeptide chains—chain A and chain B linked by disulphide bridges.
- In mammals, insulin is synthesised as a pro-hormone (that needs to be processed to become mature and functional hormone). It contains an extra stretch called C peptide.
- C peptide is absent in mature insulin and is removed during maturation into insulin.

Question: Why do lepidopterans die when they feed on Bt cotton plant? Explain how does it happen.
Answer. Bt cotton contains inactive toxin protein or protoxin. These are insecticidal proteins in the form of crystal protein. Once the insect ingests its, the inactive protoxin is converted into active form due to alkaline pH in the gut, which solubilise the crystals. The activated toxins bind to the surface of midgut epithelial cells, thus creating pores which causes cell swelling and lysis, eventually leading to the death of the insect pest.

Question: Name the process involved in the production of nematode-resistant tobacco plants, using genetic engineering. Explain the strategy adopted to develop such plants. 
Answer. The process involved in the production of nematode-resistant plants is RNA interference or RNAi.
Using Agrobacterium vectors, nematode-specific genes were introduced into the host plant. The introduction of DNA was such that it produced both sense and antisense RNA in the host cells.

These two RNA’s being complementary to each other formed a double stranded RNA (dsRNA) that initiated RNAi and thus, silenced the specific mRNA of the nematode. The consequence was that the parasite could not survive in a transgenic host expressing specific interfering RNA. The transgenic plant, therefore, got itself protected from the parasite.

Question: (a) How do organic farmers control pests? Give two examples.
(b) State the difference in their approach from that of conventional pest control methods.
Answer. (a) By natural predation or biological control.
Examples: Lady bird used to kill aphids, dragon flies used to kill mosquitoes, Bacillus thuringiensis used to kill cotton bollworm.
(b) (table 450)

Question: (a) List any four beneficial effects of GM plants.
(b) Explain how has Bacillus thuringiensis contributed in developing resistance to cotton bollworms in cotton plants. 
Answer. (a) (i) Increases tolerance against abiotic stresses (cold, drought, salt, heat).
(ii) Reduces reliance on chemical pesticides (pest-resistant crops).
(iii) Reduces post-harvest losses.
(iv) Increases efficiency of minerals used by plants (this prevents early exhaustion of fertility of soil).
(v) Enhances nutritional value of food, e.g., vitamin ‘A’ enriched rice (golden rice). (Any four)
(b) Bt cotton
- Some strains of Bacillus thuringiensis produce proteins that kill some insects like lepidopterans (tobacco budworm,armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).
- B. thuringiensis forms protein crystals which contain a toxic insecticidal protein.
- Bt toxins are initially inactive protoxins but after ingestion by the insect their inactive toxin becomes active due to the alkaline pH of the gut, which solublises the crystals.

Question: Name the host plant and the part that Meloidogyne incognita infects. Explain the role of Agrobacterium in production of dsRNA in host plant. 
Answer. Meloidogyne incognita infects the roots of tobacco plant.
For role of Agrobacterium, Pest resistant plants
- A nematode Meloidogyne incognita infects the roots of tobacco plants which reduces the production of tobacco.
- It can be prevented by using RNA interference (RNAi) process which is checked by silencing of specific mRNA due to a complementary dsRNA.
- dsRNA binds and prevents translation of the mRNA (silencing).
- The source of this dsRNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) which replicate through an RNA intermediate.

Question: How did the process of RNA interference help to control the nematode from infecting roots of tobacco plants? Explain. 
Answer. Using Agrobacterium vectors, nematode specific genes are introduced into host plant. The introduction of DNA produced both sense and anti sense RNA in host cells. These two RNA’s being complementary formed a double stranded RNA (dsRNA) that initiated RNAi and silenced the specific mRNA of the nematode. As a result, the parasite could not survive in the transgenic host expressing specific interfering RNA.

Question: Gene expression can be controlled with the help of RNA molecule. Explain the method with an example. 
Answer. Gene expression can be controlled by using RNA molecule and this technology is called RNA interference or RNAi. It is used to block the expression of certain genes and also referred to as gene silencing. During this process, RNA complementary to mRNA being produced by the gene, is introduced into the cell. This RNA binds to the mRNA making it double stranded and therefore stops its translation. Resistance to nematode Meloidogyne incognita in tobacco has been achieved by this method.