CBSE Class 12-science Answered

(a) Strategies adopted by flowering plants to prevent self-pollination:

1. Herkogamy: Flowers possess some mechanical barrier on their stigmatic surface to avoid self-pollination.

2. Dichogamy: Pollen and stigma of the flower mature at different times to avoid self-pollination.

3. Self-incompatibility: In same plants, the mature pollen fall on the receptive stigma of the same flower but fail to bring about self-pollination.

4. Male sterility: The pollen grains of some plants are not functional. Such plants set seeds only after cross-pollination.

5. Dioecism: Cross-pollination always occurs when the plants are unisexual and dioecious.

6. Heterostyly: The flowers of some plants have different lengths of stamens and styles so that self-pollination is not possible.

(b) Geitonogamy is also referred to as genetical autogamy because it refers to the fusion of male and female gamete from genetically similar plant.