Biodiversity, Conservation and Environmental Issues — BIOLOGY STD 12 Science — Question

Explain with the help of suitable examples the three different ways by which organisms overcome their stressful conditions lasting for short duration.

1. Do all pollen grains remain viable for the same length of time? Support your answer with two suitable examples.
2. How are pollen grains stored in pollen banks? State the purpose of storing pollen grains in these banks.

Explain the following terms: (a) Gene mutation (b) Genetic recombination (c) Gene flow

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.

A normal visioned woman, whose father is colour blind, marries a normal visioned man. What would be probability of her sons and daughters to be colour blind? Explain with the help of a pedigree chart.

Explain why Bt cotton flowers undergo pollination by butterflies and bees inspite of being insect pest resistant?

1. Name two groups of plants each, which have a:

1. Haploid body and
2. Diploid body.

2. What is meant by gamete transfer?

Identify 'a', 'b', 'c', 'd', 'e' and 'f' in the table given below:

No.	Syndrome	Cause	Characteristics of affected individual	Sex Male/Female/Both
1	Down’s	Trisomy of 21	‘a’ (i) (ii)	'b'
2	‘c’	XXY	Overall masculine development	‘d’
3	Turner’s	45 with OX	‘e’ (i) (ii)	‘f’

Draw a diagram of the microscopic structure of human sperm. Label the following parts in it and write their functions.

1. Acrosome.
2. Nucleus.
3. Middle piece.

OR
Draw a diagram of a human sperm. Label only those parts along with their functions, that assist the sperm to reach and gain entry into the female gamete.

Why are adolescents especially advised not to smoke? How does smoking affect the functioning of the body?