Q24 of 49 Page 1

A. When a seed of an orange is squeezed, many embryos, instead of one are observed. Explain how it is possible.

B. Are these embryos genetically similar or different? Comment.

A. When a seed of an orange is squeezed, instead one, many embryos are observed in it. This happens due to the phenomenon called polyembryony. Polyembryony may arise due to the development of embryos from synergies or from antipodal. Some embryos can also be developing from sporophyte cells of ovule such as nucellus or integument.


B. The embryos develop as a result of polyembryony are genetically similar. The embryos developing from gametophytic tissues such as synergies and antipodal are similar to each other, but not to their parents. Similarly, the embryos that are formed from sporophyte tissues are usually similar to each other as well as their parents.


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22

Describe the inter-relationship between productivity, gross primary productivity and net productivity.

 23

It is commonly observed that parents feel embarrassed to discuss freely with their adolescent children about sexuality and reproduction. The result of this parental inhibition is that the children go astray sometimes.

A. Explain the reasons that you feel are behind such embarrassment amongst some parents to freely discuss such issues with their growing children.


B. By taking one example of a local plant and animal, how would you help these parents to overcome such inhibitions about reproduction and sexuality?

 24

A. Explain the following phases in the menstrual cycle of a human female:

(i) Menstrual phase


(ii) Follicular phase


(iii) Luteal phase


B. A proper understanding of menstrual cycle can help immensely in family planning. Do you agree with the statement? Provide reasons for your answer.

 25

A. Compare, giving reasons, the J-shaped and S-shaped models of population growth of a species.

B. Explain ‘‘fitness of a species’’ as mentioned by Darwin.