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) 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 ?
Differentiate between primary and secondary succession. Provide one example of each.
| Primary Succession | Secondary Succession |
| Succession takes place on barren area. |
Occurs in an area which has been denuded recently. |
| Seral stages are many | Seral stages are few |
| Rate of succession is very slow | Rate of Succession is fast |
| Soil is absent at the time of beginning of primary succession. | Soil is present in the area where secondary succession begins. |
| Primary succession takes a long time for completion, 1000 years or more. | Secondary succession takes less time for completion. 50-200 years. |
| For eg - Forest that grew on barren land. | For eg - Trees growing on a burnt area. |
(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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