Reproduction in Lower and Higher Animals — BIOLOGY STD 12 Science — Question

With the help of a suitable diagram describe the structure of a nucleosome. 

Give reasons: Proliferative phase is also called follicular phase.

Study the graph given below and answer the questions that follow:

1. What is the relationship between dissolved oxygen and biochemical oxygen demand (BOD)?
2. Mention their effect on aquatic life in the river.

State any three methods by which animals cope with the temporary unfavourable conditions in their habitat when they cannot migrate.

Two types of aquatic organisms in a lake show specific growth patterns as shown below, in a brief period of time. The lake is adjacent to an agricultural land extensively supplied with fertilizers.
Answer the questions based on the facts given above:

1. Name the organisms depicting the patterns A and B.
2. State the reason for the growth pattern seen in A.
3. Write the effects of the growth patterns seen above.

The cytological observations made in a number of insects led to the development of the concept of genetic/ chromosomal basis of sex-determination mechanism. Honey bee is an interesting example to study the mechanism of sex-determination. Study the schematic cross between the male and the female honey bees given below and answer the questions that follow:

1. Identify the cell divisions ‘A’ and ‘B’ that lead to gamete formation in female and male honey bees respectively.
2. Name the process ‘C’ that leads to the development of male honey bee (drone).

Comment on the essential features required for an ideal contraceptive.

A woman has certain queries as listed below, before starting with contraceptives pills. Answer them.

1. What do contraceptive pills contain and how do they act as contraceptives?
2. What schedule should be followed for taking these pills?

What is a connecting link? Give suitable examples of connecting links.

1. Identify the polarity at A and B respectively in the figure given below.
2. Explain the mechanism the figure represents.