Which one of the following statements is not true with respect to viability of mammalian sperm?

Options

A. Survival of sperm depends on the pH of the medium and is more active in alkaline medium
B. Vibility of sperm is determined by its motility
C. sperms must be concentrated in a thick suspension
D. Sperrm is viable for only up to 24 hours

Answer

To determine which statement is not true with respect to the viability of mammalian sperm, we can analyze each statement provided in the question:

1. **Survival of the sperm depends upon the pH of the medium and it is more active in the alkaline medium.**
- This statement is true. Sperm survival is indeed influenced by the pH of the medium, and they are more active in alkaline conditions, which is why semen has an alkaline pH.

2. **The viability of the sperm is determined by its motility.**
- This statement is also true. Viability is often assessed by the motility of the sperm, as motility is a key indicator of the sperm's health and ability to fertilize an egg.

3. **Sperm must be considered in a thick suspension.**
- This statement is true as well. Sperm are typically found in a thick suspension within semen, which aids in their mobility and survival.

4. **The sperm is viable only for 24 hours.**
- This statement is false. The viability of mammalian sperm is generally around 72 hours, not just 24 hours.

Based on this analysis, the statement that is not true regarding the viability of mammalian sperm is the fourth one: "The sperm is viable only for 24 hours."

### Final Answer:
The statement that is not true with respect to the viability of mammalian sperm is: "The sperm is viable only for 24 hours."

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