Concept:Pollination is the transfer of pollen grains from the male reproductive part to the female reproductive part of a flower.
Explanation:Pollination is defined as the transfer of pollen grains from the stamen, which is the male reproductive organ, to the stigma, which is the female reproductive part of a flower.
The stamen produces pollen grains in its anther, while the stigma is the receptive tip of the pistil.
This transfer is a vital step before fertilization, as it brings the male gamete near the female gamete.
Pollination can occur through various agents such as wind, water, insects, and other animals.
When pollen is transferred within the same flower or to another flower on the same plant, it is called self-pollination.
When pollen is transferred from one plant to a flower on a different plant, it is called cross-pollination, which increases genetic diversity.
Option A is incorrect because insects merely act as carriers; their visit is not pollination itself.
Option B is incorrect because the growth of the pollen tube in the ovule happens after pollination, during fertilization.
Option C is incorrect because germination of pollen grains occurs on the stigma after pollination has already taken place.
Thus, the only correct definition is given in option D.
Answer:Option D — Pollination is the transfer of pollen grains from stamen to stigma.