How does fertilization occur in plants?

Fertilization in plants occurs when a pollen grain, which contains male gametes, lands on the stigma of a flower. The stigma is a part of the female reproductive structure, known as the pistil. Once the pollen grain successfully adheres to the stigma, it begins to germinate and grows a pollen tube down through the style towards the ovule located in the ovary. This process is essential for the transfer of the male gametes to the ovule, where fertilization takes place.

In contrast to the other choices, the correct answer accurately describes the process where a pollen grain not only lands on the stigma but also grows a tube that allows the sperm cells to reach the ovule for fertilization. The other options do not accurately depict the fertilization process in plants. For instance, pollen growing on the root doesn't occur in the typical reproductive process of flowering plants, and female gametes do not move through the soil; they remain within the ovule. While a flower opening to release pollen is part of the reproductive cycle, it does not specifically describe the process of fertilization itself, which requires the actions following pollen landing on the stigma.