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

Step 1 : Understanding the Question:
The question asks for the correct spatial sequence of the protective envelopes and spaces surrounding a mature human egg (ovum), specifically ordering them starting from the outermost layer and moving inward to the cell membrane.
Step 2 : Key Formulas and Approach:
The approach involves identifying the origin and position of each barrier:
1. Outer Cellular Coat: Granulosa cells.
2. Protective Glycoprotein Shell: Acellular coating.
3. Fluid-filled Gap: Space just outside the membrane.
4. Cell Boundary: The oolemma.
Step 3 : Detailed Explanation:

Outermost Layer (Corona Radiata - C): When the ovum is released from the follicle during ovulation, it is accompanied by a radiating crown of follicular cells (granulosa cells). These cells form the outermost cellular barrier that a sperm must navigate through.

Primary Envelope (Zona Pellucida - A): Beneath the corona radiata is a thick, transparent, and acellular layer of glycoproteins. This layer is secreted by the egg itself and is crucial for species-specific sperm recognition and the prevention of polyspermy.

Intermediate Space (Perivitelline Space - B): This is a thin, fluid-filled gap located between the zona pellucida and the plasma membrane of the ovum. It is important because the first and second polar bodies are extruded into this space during meiotic maturation.

Innermost Boundary (Plasma Membrane - D): This is the actual biological cell membrane (also called the oolemma) that encloses the egg's cytoplasm (ooplasm). This is the final layer that the sperm must fuse with for fertilization to succeed.

Step 4 : Final Answer:
Arranging these anatomical features from outer to inner yields the sequence: Corona radiata $\rightarrow$ Zona pellucida $\rightarrow$ Perivitelline space $\rightarrow$ Plasma membrane. This corresponds to the sequence C, A, B, D. Therefore, the correct answer is option (B).