Question

Which of the following mechanism favours self-pollination ?

• A. Protandry
• B. Cleistogamy
• C. Protogyny
• D. Dioecy

Hint:

Mechanisms influencing pollination type:
Favouring Self-Pollination:
Cleistogamy: Flowers never open, ensuring self-pollination (e.g., some violets, peas).
Bisexual flowers where anthers and stigma mature simultaneously and are close.
Favouring Cross-Pollination:
Protandry (anthers mature first).
Protogyny (stigma matures first).
Dioecy (separate male and female plants).
Self-incompatibility.

Answer 1

The Correct Option is B

Self-pollination is the transfer of pollen from the anther to the stigma of the same flower or another flower on the same plant. Certain floral mechanisms promote self-pollination, while others promote cross-pollination.
(1) Protandry: A condition where the anthers (male parts) of a flower mature and release pollen before the stigma (female part) of the same flower becomes receptive. This promotes cross-pollination by preventing self-pollination.
(2) Cleistogamy: A condition where pollination and fertilization occur within unopened, self-contained flowers. Since the flowers do not open, cross-pollination is prevented, and self-pollination is ensured. This is an effective mechanism favouring self-pollination.
(3) Protogyny: A condition where the stigma of a flower becomes receptive before the anthers of the same flower release pollen. This also promotes cross-pollination.
(4) Dioecy: A condition where individual plants are either male (producing only staminate flowers) or female (producing only pistillate flowers). This enforces cross-pollination between different plants. Therefore, cleistogamy is the mechanism among the options that unequivocally favours self-pollination. Cleistogamy

Answer 2

Definition-matching approach: The word cleistogamy comes from the Greek kleistos (closed) and gamos (marriage/mating), literally, flowers that mate while closed. Because the flower never opens, external pollen carriers (wind, insects) cannot reach the stigma, so fertilization must happen using the flower's own pollen. This structurally guarantees self-pollination. In contrast, protandry and protogyny both stagger the maturity of anthers and stigma within the same flower specifically to avoid self-fertilization, and dioecy separates male and female flowers onto different plants altogether, making self-pollination impossible. Only cleistogamy structurally forces self-pollination, so it is the correct choice.