Wind-pollinated and water-pollinated flowers produce an enormous amount of pollen when compared to the number of ovules available for pollination. What is the reason for this?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Pollen grains reaching the stigma is a chance factor, and the large amount of pollen makes up for the pollen grains lost
In wind and water pollination nothing guides the pollen to the stigma. Whether a pollen grain lands on a stigma is a matter of chance, and most of the pollen is lost on the way. To make up for this uncertainty and loss, these flowers produce an enormous amount of pollen compared with the number of ovules.
Option (1) Each ovule needs several pollen grains for double fertilisation to take place — Incorrect. In double fertilisation one pollen tube brings two male gametes: one fuses with the egg and the other with the polar nuclei. A single pollen grain is enough for an ovule.
Option (2) Pollen grains reaching the stigma is a chance factor, and the large amount of pollen makes up for the pollen grains lost — Correct. Pollen reaching the stigma is a chance factor in wind and water pollination, and the large amount of pollen compensates for the pollen grains lost.
Option (3) Most pollen grains lose their viability before they are released from the anther — Incorrect. Pollen grains lose viability only after release, and the period varies from about 30 minutes in rice and wheat to months in some species. They are not mostly dead before release.
Option (4) Pollen grains also serve as a floral reward for the animals that visit these flowers — Incorrect. Floral rewards such as nectar and pollen are offered by animal-pollinated flowers. Wind- and water-pollinated flowers are not very colourful and do not produce nectar, as they do not need to attract animals.
NCERT Extract:
Pollination – “… Majority of plants use biotic agents for pollination. Only a small proportion of plants use abiotic agents. Pollen grains coming in contact with the stigma is a chance factor in both wind and water pollination. To compensate for this uncertainties and associated loss of pollen grains, the flowers produce enormous amount of pollen when compared to the number of ovules available for pollination.”