## Core Concept
Capacitation of sperm in the female reproductive tract is a physiological change that spermatozoa must undergo in order to have the ability, or capacity, to penetrate and fertilize an egg. It involves a series of cellular and molecular changes.

## Why the Correct Answer is Right
The correct answer, , is related to the acrosome reaction. Capacitation enables the sperm to undergo the acrosome reaction, which is the release of enzymes from the acrosome of the sperm. These enzymes, particularly acrosin, help in dissolving the zona pellucida of the egg, allowing the sperm to penetrate and fertilize it.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option is incorrect because capacitation does not directly relate to increasing sperm motility. While motility is crucial for sperm to reach the egg, capacitation specifically refers to changes that allow the sperm to interact with and penetrate the egg.
* **Option B:** - This option is incorrect because capacitation does not involve changes in the sperm membrane that would decrease its ability to fuse with the egg; rather, it prepares the sperm for fusion with the egg.
* **Option C:** - This option might seem plausible but is not directly related to the primary role of capacitation.

## Clinical Pearl / High-Yield Fact
A key point to remember is that capacitation occurs in the female reproductive tract and is essential for fertilization to occur. This process takes about 7-10 hours and is a critical step for in vivo fertilization.

## Correct Answer Line
**Correct Answer: D. .**