Vitelline membrane is the plasma membrane or the primary egg membrane. The secondary and tertiary egg membranes include the zona pellucida and the corona radiata.

Immediate membrane covering the mammalian egg

The correct answer is option 'C', the vitelline membrane.

Explanation:

When a mammalian egg is released from the ovary, it is surrounded by various layers of protective membranes. The immediate membrane covering the mammalian egg is known as the vitelline membrane.

The vitelline membrane is a layer of extracellular matrix that surrounds the egg cell. It is composed of glycoproteins and proteins and is secreted by the egg itself. The vitelline membrane plays a crucial role in protecting the egg and regulating fertilization.

Functions of the vitelline membrane:

1. Protection: The vitelline membrane acts as a physical barrier, protecting the egg from mechanical damage and preventing the entry of foreign substances.

2. Regulation of fertilization: The vitelline membrane is involved in the process of fertilization. It contains receptors that recognize and bind to specific molecules on the surface of sperm cells. This interaction triggers a series of biochemical events that allow the sperm to penetrate the vitelline membrane and fuse with the egg.

3. Prevention of polyspermy: Polyspermy is the fertilization of an egg by more than one sperm. This can be detrimental to the development of the embryo. The vitelline membrane helps prevent polyspermy by undergoing changes after the entry of the first sperm, making it impermeable to other sperm.

4. Support for embryonic development: The vitelline membrane provides structural support for the developing embryo. It allows nutrients and other essential molecules to pass through to the developing embryo while maintaining a protective environment.

In addition to the vitelline membrane, there are other layers surrounding the mammalian egg. These include the zona pellucida, a glycoprotein-rich layer that lies outside the vitelline membrane, and the corona radiata, which consists of a layer of follicular cells that surround the zona pellucida.

Overall, the vitelline membrane is the immediate membrane covering the mammalian egg and plays a vital role in protecting the egg and facilitating fertilization and embryonic development.