Final answer:
The secondary oocyte is surrounded by the zona pellucida, a crucial glycoprotein layer involved in sperm penetration and fertilization processes.
Step-by-step explanation:
A secondary oocyte is surrounded by a ring of proteins and glycoproteins called the zona pellucida.
The zona pellucida is a thick, gel-like glycoprotein membrane that coats the oocyte and is essential for the process of fertilization. This membrane must be penetrated by the sperm for fertilization to occur, leading to the formation of a zygote. During ovulation, the oocyte, also known as a secondary oocyte at this stage, is released from the ovary and is accompanied by the corona radiata, which consists of granulosa cells. The underlying zona pellucida is a key structure that plays a crucial role when capacitated sperm reach the oocyte, release digestive enzymes from the acrosome to penetrate the zona pellucida, and allow one sperm to eventually fuse with the oocyte's plasma membrane. The merger of the haploid nuclei of the sperm and the oocyte results in the creation of a diploid zygote. As the zygote travels toward the uterus, it undergoes cell divisions and, upon implantation, begins the process of embryonic development.