Question

Arrange the following cell layers/structures around the female gamete from outer to inner side :
A. Zona pellucida
B. Perivitelline space
C. Corona radiata
D. Plasma membrane of ovum
Choose the correct answer from the options given below :

• A. C, A, D, B
• B. C, A, B, D
• C. D, B, A, C
• D. A, C, B, D

Hint:

Logic Tip: Visualize the egg as a fortress. The "Crown" (Corona) is on the very outside. The thick "Zone" (Zona) is the main wall. The "Space" (Perivitelline) is the moat. The "Membrane" (Plasma) is the final door.

Answer 1

The Correct Option is B

Concept:
A mature mammalian ovum (egg) is highly specialized and is surrounded by multiple protective envelopes. A sperm must penetrate these successive layers from the outside in to successfully fertilize the ovum.
Step 1:
The outermost boundary surrounding the ovulated egg is formed by multiple layers of follicular cells (granulosa cells) that are radially arranged. This distinct cellular coat is known as the Corona radiata. First (Outermost): C
Step 2:
Immediately inside the corona radiata is a thick, transparent, and acellular glycoprotein layer secreted primarily by the oocyte itself. This primary envelope is called the Zona pellucida. Second: A
Step 3:
Between the zona pellucida and the cell membrane of the ovum, there is a narrow, fluid-filled space. This space, which later houses the extruded polar bodies, is the Perivitelline space. Third: B
Step 4:
The innermost structure bounding the actual cytoplasm (ooplasm) of the female gamete is its own cell membrane, referred to as the Plasma membrane of the ovum (or oolemma). Fourth (Innermost): D
Step 5:
Arranging these structures strictly from outer to inner yields the sequence: Corona radiata $\rightarrow$ Zona pellucida $\rightarrow$ Perivitelline space $\rightarrow$ Plasma membrane. The correct order is C, A, B, D. Therefore, Option (2) is correct.