Genetically modified plants have been useful in many ways as follows

(i) These plants are more tolerant to abiotic stresses (cold, drought, salt, heat).

(ii) They have reduced the reliance on chemical pesticides (pest-resistant crops).

(iii) They helped to reduce post harvest losses.

(iv) They increases the efficiency of mineral usage by plants (this prevents early exhaustion of fertility of soil).

(v) Enhanced nutritional value of food, e.g., vitamin-A enriched rice.

In addition to these uses, GM plants have been used to create tailor-made plants to supply alternative resources to industries, in the form of starches, fuels and pharmaceuticals.

(a) Genetically modified plants can reduce the usage of chemical pesticides by introducing pest resistant plants.

e.g., There are several nematodes that parasitie, a wide variety of plants and animals including human beings. A nematode Meloidogyne incognita infects the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infestation which was based on the process of RNA interference (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 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.

(b) Genetically modified plants can enhance nutritional value of food crops.

e.g., 'Golden rice' developed at Swiss Federal Institute of technology is an example of nutritionally modified crop. It is rich in vitamin-A ( $\beta$-carotene). The rice grains are golden-yellow in colour. It contains 'beta-carotene' gene from daffodil plant and also from some bacteria. Golden rice can prevent child blindness which is caused due to the deficiency of vitamin-A.

The disadvantages of insulin obtained from the pancreas of slaughtered cows and pigs are

(i) Insulin being a hormone is produced in very little amounts in the body. Hence, a large number of animals need to be sacrificed for obtaining small quantities of insulin. This makes the cost of insulin very high (Demand being many fold higher than supply).

(ii) Slaughtering of animals is not ethical.

(iii) There is a potential of immune response in humans against the administered insulin which is derived from animals.

(iv) There is possibility of slaughtered animals being infested with some infectious microorganism which may contaminate insulin.

The advantages of recombinant insulin are

(i) There is no need of animals to be sacrificed for the production of recombinant insulin.

(ii) Recombinant insulin was not found allergic to patients, while the insulin from an animal source caused some patients to develop allergy or other types of reactions to the foreign protein.

(iii) The cost of recombinant insulin is not very high. (Supply being many fold higher than demand).

Biopesticide is a pesticide which is

(i) Not chemical in nature.

(ii) More specific in action against the pest.

(iii) Safer for environment than chemical pesticides.

A popularly known bio-pesticide is Bt toxin, which is produced by a bacterium called Bacillus thuringiensis. Bt toxin gene has been cloned from this bacterium and expressed in plants. Bt toxin protein when ingested by the insect, gets converted to its active form due to the alkaline pH of the gut.

The activated toxin binds to the surface of midgut epithelial cells and create pores that causes swelling and lysis of the cell and eventually kills the insect.