51.

Explain the following terms:

(2) Homologous chromosomes

Explain the following terms:

(3) Alleles

Give the dihybrid ratio. Name and state the law which explains the same.

Mention three main reasons for the sharp rise in ‘human population’ in the world.

Draw a diagram of the nucleus of a cell, having chromosome number 6, as it would appear in the metaphase stage of mitosis and label the following parts in the diagram:
1. Aster
2. Achromatic spindle
3. Chromatid
4. Centromere

Mention the difference between mitosis and meiosis with reference to

1. Number of daughter cells formed at the end of the division.

2. The chromosome number of the daughter cells formed.

Account for the following briefly:

The pituitary gland is known as the ‘master gland’.

Account for the following briefly:

Animals owe their existence to chlorophyll.

Account for the following briefly:

Twins may or may not be identical.

Account for the following briefly:

(iv) Herbaceous plants growing in well-watered soils are found to wilt on a hot day.