Human Reproduction — BIOLOGY STD 12 Science — Question

Discuss the role of healthy ecosystem services as a pre-requisite for a wide range of economic, environmental and aesthetic goods and services.

If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Study the following flow chart. Name the hormones involved at each stage. Explain their functions.
Hypothalamus → Pituitary → Testes → Sperms.

1. Explain the development of female gametophyte from a megaspore mother cell in an angiosperm.
2. Draw a leballed diagram of a fully-developed embryo sac.

OR

1. Describe the process of megasporogenesis in angiosperms, until 8-nucleate stage.
2. Draw the labelled structure of mature embryo sac.

A pregnant woman who have had amniocentesistest was advised to undergo MTP. It was diagnosed by her doctor that the embryo she is carrying has an extra barr body.

1. Name the syndrome which is likely to be associated with the embryo.
2. Why was she advised to undergo MTP?
3. Do you justify the statutory ban on amniocentesis in our country Give reasons.

1. Draw the pyramids of biomass in a pond and in a forest. Explain giving reasons why the two pyramids are different.
2. Pyramid of energy is always upright. Explain.

Explain in detail the various reagents of pollination.###How many types of pollination are there? Write a brief note and explain any one abiotic factor of pollination with an example.

The number of trophic levels in an ecosystem are limited. Comment.

Naman entered into a quarrel with some farmers who were spraying DDT in their field. Many people gathered at the spot to see and enjoy the incident. The angry mob demanded that Naman should not interfere in the farmer's job. Naman tried to explain his point and finally succeeded in explaining the harmful effects of DDT.

1. What is biomagnification? Explain with an example.
2. Is biomagnification related with DDT only? Comment.
3. What is the effect of DDT on birds?
4. What values did Naman promote?

For the selection of recombinants, insertional inactivation of the antibiotic marker has been superseded by insertional inactivation of a marker gene coding for a chromogenic substrate. Give reasons.