Short Answer Type(a) How do organic farmers control pests ? Give two examples.
(b) State the difference in their approach from that of conventional pest control methods.
(a) The organic farmers control pests by using the plants genetically modified for pest resistance. Usually, the gene that makes the plant resistant to the pest is introduced into the plant.
For Example -
i. Bt Cotton : The cotton plants were incorporated with the Bt toxin gene of the bacterium Bacillus thringiensis. The gene known as the cry gene provided the cotton crops resistance against the bollworms.
ii. The nematode Meloidogyne incognita infects the roots of tobacco plant and causes reduction in yield. RNA interference (RNA i) involve silencing of a specific RNA. Using agrobacterium vectors, Nematode specific gene is introduced into host plant. The introduction of DNA was such that it produced both sense and antisense RNA into the host cells. These two RNAs being complementary to each other formed a double-stranded RNA that initiated RNA interference reaction and provided protection against the pest.
(b) In conventional pest control, various pesticides were sprayed on the crops or agricultural fields to provide protection against the pests. This usually killed the good insects or organisms too and was responsible for pollution too. The pesticides used were toxic to animals and humans too.
However, the organic farming does not involve the use of pesticides and hence caused less pollution and toxic in nature.
(a) Name the selectable markers in the cloning vector pBR322 ? Mention the role they play.
(b) Why is the coding sequence of an enzyme 
-galactosidase a preferred selectable marker in comparison to the ones named above ?
(a) Why must a cell be made 'competent' in biotechnology experiments ? How does
calcium ion help in doing so ?
(b) State the role of 'biolistic gun' in biotechnology experiments.
Long Answer TypeA large number of married couples the world over are childless. It is shocking to know that in India the female partner is often blamed for the couple being childless.
(a) Why in your opinion the female partner is often blamed for such situations in India ? Mention any two values that you as a biology student can promote to check this social evil.
(b) State any two reasons responsible for the cause of infertility.
(c) Suggest a technique that can help the couple to have a child where the problem is with the male partner.
(a) What is polygenic inheritance ? Explain with the help of a suitable example.
(b) How are pleiotropy and Mendelian pattern of inheritance different from polygenic pattern of inheritance ?
(a) Name the stage in the cell cycle where DNA replication occurs.
(b) Explain the mechanism of DNA replication. Highlight the role of enzymes in the process.
(c) Why is DNA replication said to be semiconservative ?
(a) Name the two growth models that represent populations growth and draw the respective growth curves they represent.
(b) State the basis for the difference in the shape of these curves.
(c) Which one of the curves represent the human population growth at present ? Do you think such a curve is sustainable ? Give reason in support of your answer.
(a) Taking an example of a small pond explain how the four components of an ecosystem function as a unit.
(b) Name the type of food chain that exists in a pond.
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