Which of the following statements are correct?
(A) Continued cross-pollination results in inbreeding depression.
(B) In castor and maize, the production of unisexual flowers prevents autogamy but not geitonogamy.
(C) In papaya, male and female flowers are present on the same plant, and this prevents both autogamy and geitonogamy.
(D) The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible).
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → B and D only
Most flowering plants have bisexual flowers, so self-pollination is likely. Plants have several outbreeding devices to discourage it. One is to bear unisexual flowers: on the same plant (monoecious) or on different plants (dioecious). Autogamy is pollination within the same flower; geitonogamy is pollination between flowers of the same plant.
(A) Continued cross-pollination results in inbreeding depression. — False. Inbreeding depression comes from continued self-pollination. Cross-pollination is what plants encourage to avoid it.
(B) In castor and maize, the production of unisexual flowers prevents autogamy but not geitonogamy. — True. Castor and maize are monoecious. A unisexual flower cannot pollinate itself, but pollen can still reach another flower of the same plant.
(C) In papaya, male and female flowers are present on the same plant, and this prevents both autogamy and geitonogamy. — False. Papaya is dioecious: male and female flowers are on different plants. Only this condition prevents both autogamy and geitonogamy.
(D) The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible). — True. This is the start of pollen-pistil interaction. The pistil accepts compatible pollen and rejects incompatible pollen.
NCERT Extract:
Pollination – “… Outbreeding Devices : Majority of flowering plants produce hermaphrodite flowers and pollen grains are likely to come in contact with the stigma of the same flower. Continued self-pollination result in inbreeding depression. … Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy. In several species such as papaya, male and female flowers are present on different plants, that is each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.”
Pollination – “… The pistil has the ability to recognise the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible).”