Which is the correct sequence of layers in the mammalian egg from outside to inside?

Options

A. Zona pellucida, corona radiata, plasma membrane
B. Corona radiata, zona pellucida, plasma membrane
C. Plasma membrane, zona pellucida, corona radiata
D. None of the above

Answer

To determine the correct sequence of layers in the mammalian egg from outside to inside, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Outermost Layer**:
- The outermost layer of the mammalian egg is the **corona radiata**. This layer is composed of follicular cells and provides essential proteins for the development of the ovum.

2. **Identify the Middle Layer**:
- The next layer, located just beneath the corona radiata, is the **zona pellucida**. This layer is a glycoprotein structure that plays a crucial role in the binding of spermatozoa and is involved in the acrosomal reaction.

3. **Identify the Innermost Layer**:
- The innermost layer is the **plasma membrane** of the egg cell itself. This membrane surrounds the cytoplasm of the egg and is essential for maintaining the integrity of the cell.

4. **Sequence the Layers**:
- Based on the identification of the layers, the correct sequence from outside to inside is: **corona radiata**, **zona pellucida**, and **plasma membrane**.

5. **Select the Correct Option**:
- Among the provided options, the correct answer is the second option: **corona radiata, zona pellucida, plasma membrane**.

### Final Answer:
The correct sequence of layers in the mammalian egg from outside to inside is: **corona radiata, zona pellucida, plasma membrane**.

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