Final answer:
The union of gametes is called fertilization, a key process in sexual reproduction that results in genetic diversity. It occurs when a sperm cell from pollen fuses with an egg cell in the ovule, forming a diploid zygote. The correct option is b) fertilization
Step-by-step explanation:
The union of gametes is called fertilization. This process is critical for sexual reproduction in both angiosperms and gymnosperms. In the context of plants, fertilization occurs when the male gamete (sperm) from a pollen grain enters the ovule sac and fertilizes the female gamete (egg), leading to the formation of a diploid zygote. This event is a vital part of the pollination and fertilization process that enables genetic diversity through sexual reproduction.
Pollination, which is the transfer of pollen from an anther to a stigma, can occur through self-pollination or cross-pollination with the help of agents such as wind, water, or animals. After pollination, the formation of a pollen tube allows the transfer of sperm to the egg. In angiosperms, this process leads to double fertilization, where one sperm fertilizes the egg to form a zygote, and the other combines with the polar nuclei forming the endosperm.