Q20 of 51 Page 1

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.

A. The DNA is a hydrophilic molecule. It cannot pass through cell membranes. In order to pass DNA into the bacterial cell, the bacterial cells must made ‘competent’ to take up DNA. This is done by treating the cell with a specific concentration of a divalent cation, such as calcium ions (Ca++) which increases the efficiency with which DNA can enters the bacterium through pores in its cell wall.


B. The biolistic or gene gun is a method to introduce alien DNA into the plant cells. In this method plants, cells are bombarded with high velocity micro-particles of gold or tungsten coated with DNA. Thus, the recombinant DNA is transferred into the plant cell.


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Predation is usually referred to as a detrimental association. State any three positive roles that a predator plays in an ecosystem.

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A. How do organic farmers control pests? Give two examples.

B. State the difference in their approach from that of conventional pest control methods.

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Give a genetic explanation for the following cross. When a tall pea plant with round seeds was crossed with a dwarf pea plant with wrinkled seeds then all the individual of F1-populations was tall with round seeds. However selfing among F1-population led to a 9: 3 3 : 1 phenotypic ratio.

 25

A. Describe the series of experiments of F.Griffith. Comment on the significance of the results obtained.

B. State the contribution of Macleod, McCarty and Avery.