1)pollen grain is a minute body, of varying shape and structure, formed in the male structures of seed-bearing plants and transported by various means (wind, water, insects, etc.) to the female structures, where fertilization occurs.

2)One of the granular microspores that occur in pollen and give rise to the male gametophyte of a seed plant

Pollen Grain in Sexual Reproduction in Flowering Plants

Pollen Grain Structure:
- Pollen grains are the male gametophytes of flowering plants.
- They are produced in the anthers of the flower and contain the male gametes.
- Each pollen grain is a single cell enclosed within a tough outer wall called the exine.

Pollen Transfer:
- Pollen grains are transferred from the anthers to the stigma of the same or another flower through various agents like wind, water, insects, or birds.
- This process is called pollination.

Germination of Pollen Grain:
- Once a pollen grain lands on the stigma, it absorbs water and germinates.
- The pollen tube grows out of the pollen grain and enters the style of the pistil.

Fertilization:
- The pollen tube carries the male gametes to the ovule in the ovary of the flower.
- Fertilization occurs when the male gametes fuse with the female gametes in the ovule to form a zygote.

Formation of Seeds and Fruits:
- The zygote develops into an embryo, and the ovule matures into a seed.
- The ovary of the flower develops into a fruit that protects the seeds and aids in their dispersal.

Overall, pollen grains play a crucial role in sexual reproduction in flowering plants by transferring male gametes to the female reproductive organs, leading to the formation of seeds and fruits. This process ensures genetic diversity and the continuation of plant species.