Question

Layers of an ovum from outside to inside is
A. corona radiata, zona pellucida and vitelline membrane
B. zona pellucida, corona radiata and vitelline membrane
C. vitelline membrane, zena uelludda and corona radiata
D. zona pellucida, vitelline membrane and corona radiata.

Answer 1

Ovum is nothing but egg, where they generally produced in females before the birth itself but they are immature, at the age of puberty, they have attain the mature stage or ripened, by the release of the hormone, they released from the ovary, and only egg or ovum is released and the process is called as ovulation.

Complete step by step answer: The layer of ovum from outside to inside are corona radiata, and the Zona pellucida, and Vitelline membrane.
Corona radiata: It is the innermost layer of the cells of the granules oophorus and it is directly adjacent to Zona pellucida, which is an inner protective layer of the ovum.
The main purpose of this layer is to supply proteins to cells and it is formed by follicles adhering to the oocyte before it leaves the ovarian follicles and originates from the squamous granulosa cells.
The corona radiata formed from the granulosa cells enlarge and become cuboidal cells, this transition occurs during primordial to primary oocyte.
Zona Pellucida: It is specialized extracellular matrix surrounding the developing oocyte, within each follicle and the zona pellucida is surrounded by the corona radiata, and the zona pellucida is a glycoprotein layer that surrounding the plasma membrane of mammalian oocyte, Zona pellucida have Zp3 glycoprotein, which is responsible for sperm binding, after fertilization, zona pellucida degenerates and it is replaced by the trophoblast.
Vitelline membrane: Vitelline membrane is also called a vitelline envelope, and it is a structure that surrounds the outer surface of the plasma membrane of the ovum, and it is mostly composed by protein fibers, and with protein receptors which are needed for sperm binding.
So the correct option is A.

Note: In females before an ovum can be fertilized, it must undergo process of maturation or ripening which takes place previous or immediately after it escapes from follicle and it undergoes unequal subdivision of ovum, and at first, two cells are formed and then 4 cells are formed, and out of them 3 convert to polar bodies and one becomes mature ovum.