10. Explain the mechanisms underlying the blocks to polyspermy?

The mechanisms underlying the blocks to polyspermy are as follows:<br /><br />1. **Fast Block to Polyspermy**: This is the initial and immediate response to prevent multiple sperm from fertilizing a single egg. It involves the rapid depolarization of the egg membrane, which changes the electrical charge of the egg surface, making it less attractive to sperm and physically repelling them. This depolarization is triggered by the influx of sodium ions through voltage-gated channels.<br /><br />2. **Slow Block to Polyspermy**: This is a slower, more permanent mechanism that ensures no additional sperm can fertilize the egg after the first sperm has already done so. This block is achieved through the formation of a fertilization envelope. When the first sperm penetrates the egg, cortical granules located just beneath the egg's plasma membrane release their contents into the space between the plasma membrane and the zona pellucida. This release causes the zona pellucida to harden and the fertilization envelope to form, which acts as a physical barrier to prevent other sperm from reaching the egg.<br /><br />Together, these mechanisms ensure that only one sperm fertilizes the egg, preventing polyspermy and ensuring proper development.