For the completion of fertilization which sequence of layers (outer to inner) are crossed by sperm ?

Options

A. Theca externa – Theca media – Corona radiata – Zona pellucida – Plasma membrane of oocyte
B. Corona radiata – Zona pellucida – Perivitelline space – Plasma membrane of oocyte
C. Zona pellucida – Corona radiata – Theca externa
D. Theca interna – Zona pellucida – Corona radiata – Plasma membrane of oocyte

Answer

To determine the sequence of layers crossed by the sperm during fertilization, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Layers of the Ovum**:
- The ovum has several layers surrounding it. The main layers are:
- **Corona Radiata**: The outermost layer.
- **Zona Pellucida**: The layer beneath the corona radiata.
- **Pre-Vitaline Space**: The space between the zona pellucida and the plasma membrane.
- **Plasma Membrane**: The innermost layer that surrounds the cytoplasm of the ovum.

2. **Sequence of Layers Crossed by Sperm**:
- When a sperm approaches the ovum, it first encounters the **Corona Radiata**.
- After penetrating the corona radiata, the sperm moves to the **Zona Pellucida**.
- Next, the sperm crosses the **Pre-Vitaline Space**.
- Finally, the sperm reaches the **Plasma Membrane** of the ovum.

3. **Final Sequence**:
- Therefore, the correct sequence of layers crossed by the sperm from outer to inner is:
- **Corona Radiata → Zona Pellucida → Pre-Vitaline Space → Plasma Membrane**.

4. **Choose the Correct Option**:
- Based on the identified sequence, we can compare it with the provided options to find the correct one. The correct answer matches the sequence identified above.