Pollen grains don't contain sperm. Pollen grains contain pollen tubes, which deliver sperm to the egg cell in the ovary of a flower.

Here's how it works:

* Pollen lands on the stigma: When a pollen grain lands on the stigma (the sticky top part of the pistil), it germinates.

* Pollen tube grows: The pollen grain forms a pollen tube that grows down through the style (the stalk connecting the stigma to the ovary).

* Sperm travel: The pollen tube carries two sperm cells to the ovary, where the ovules (egg cells) are located.

* Fertilization: One sperm cell fertilizes the egg cell, leading to the formation of a zygote, which will develop into the embryo of a new plant.

So, the function of the sperm within the pollen tube is to fertilize the egg cell and initiate the formation of a new plant.