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 ?
(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) DNA replication takes place in the S phase or Synthetic phase of the Cell cycle.
(b) The process of Replication;
1. The double-helix structure of the DNA unzips. This is carried out by an enzyme called helicase which breaks the hydrogen bonds holding the complementary basesof DNA together
2. The DNA do not separate completely but at some point. The separation of the two single strands of DNA creates a ‘Y’ shape called a replication ‘fork’. The two separated strands act as templates for making the new strands of DNA.
3. One of the strands is oriented in the 3’ to 5’ direction and is called the leading strand. The other strand is oriented in the 5’ to 3’ direction and is the lagging strand. As a result of their different orientations, the two strands are replicated differently:
4. Leading Strand:
A short piece of RNA called a primer (produced by an enzyme called primase) comes along and binds to the end of the leading strand. The primer acts as the starting point for DNA synthesis.
DNA polymerase binds to the leading strand and then ‘walks’ along it, adding new complementary nucleotide bases (A, C, G and T) to the strand of DNA in the 5’ to 3’ direction. This sort of replication is called continuous.
Lagging strand:
Numerous RNA primers are made by the primase enzyme and bind at various points along the lagging strand. Chunks of DNA, called Okazaki fragments, are then added to the lagging strand also in the 5’ to 3’ direction. This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later.
5. Once all of the bases are matched up (A with T, C with G), an enzyme called exonuclease strips away the primer(s).
6. Finally, an enzyme called DNA ligase seals up the sequence of DNA into two continuous double strands. The result of DNA replication is two DNA molecules.
(c) The newly formed two DNA strands consist of one new and one old chain of nucleotides. This is why DNA replication is described as semi-conservative, half of the chain is part of the original DNA molecule, half is new
(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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