Question

In humans, during fertilization, a sperm firstly comes in contact with which layer of the ovum?
A. Zona pellucida
B. Vitelline membrane
C. Jelly coat
D. Corona Radiata

Answer 1

Hint: Fertilization is a process in which the male gamete, also known as sperm fertilizes the female gamete that is egg or ovum to form a zygote inside the female body. This is also known as sexual reproduction.

Complete answer: The reproduction is a biological process by which an organism produces new offsprings. There are two methods of reproduction; asexual reproduction and sexual reproduction. Asexual reproduction, on the other hand, is a reproduction in which offsprings arise from a single parent. Sexual reproduction is a mode of reproduction, in which, offsprings arises from two parents from the opposite sex. In humans, the male gamete sperm is a motile gamete that reaches the female gamete ovum for fertilization. The human egg or ovum is the mature female gamete that develops from the primitive germ cells embedded in the cortex of the ovaries. Each of the primitive germ cells gives rise to a number of small cells called oogonia through repeated divisions. Oogonia develop into primary oocytes and then into the mature ovum. The ovum is spherical in shape and is enclosed in the follicles of the ovary. The ooplasm in the cytoplasm of the ovum, the nucleus is known as the germinal vesicle and the nucleolus is known as the germinal spot. Ovum is covered with many layers, the innermost layer is known as Zona pellucida whereas the outer layer is known as Corona Radiata. Whenever a sperm comes in contact with the ovum during fertilization, the first layer that sperm interacts with is Corona Radiata.
Hence, the correct answer is option D.

Note: The cells of Corona Radiata are arranged radially around the zona pellucida when the ovum is released from the follicle. Sperms when penetrated through Corona Radiata, it undergoes a spontaneous acrosomal reaction, which releases digestive enzymes that digest the extracellular matrix of the Corona Radiata.