Give reasons: An ovum allows the entry of only one sperm at a time.

Explanation

### Step-by-Step Solution:

1. **Understanding Fertilization**: Fertilization is the process where a sperm cell fuses with an ovum (egg cell) to form a zygote. This is a crucial step in sexual reproduction.

2. **Entry of Sperm**: When a sperm successfully penetrates the ovum, it triggers a series of changes in the egg cell.

3. **Depolarization of the Ovum**: Upon the entry of the first sperm, the ovum undergoes a process called depolarization. This means that the electrical charge across the membrane of the ovum changes.

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