What is the primary role of the pollen tube in plant reproduction?

The primary role of the pollen tube in plant reproduction is to deliver sperm cells to the embryo sac. When a pollen grain lands on a compatible stigma, it germinates and forms this tube, which grows down through the style towards the ovule located in the ovary. This process is essential for fertilization to occur; the tube provides a conduit for the sperm cells to travel from the pollen grain directly to the egg cell within the embryo sac. Once the sperm cells reach the embryo sac, one sperm fuses with the egg cell to form the zygote, while the other might fuse with two polar nuclei to form the endosperm, crucial for seed development. The successful transport and delivery of the sperm cells via the pollen tube is a vital step in the sexual reproduction of flowering plants.

Other options do not directly relate to the role of the pollen tube. For instance, while absorbing nutrients from the soil is important for plant growth, it is unrelated to the functions of the pollen tube. Pollination refers to the process of transferring pollen from one flower to another, also distinct from the pollen tube's role, while the production of seeds is a result of successful fertilization and not the direct function of the pollen tube itself.