Infertility could develop when the sperm cells display ......

Options

A. a count of `120` million per ml semen
B. increased acrosomal activity
C. normal morphology
D. a count of less than `20` million per ml semen

Answer

To answer the question "Infertility could develop when the sperm cells display ......", we need to analyze the options provided and understand the factors that contribute to male infertility.

### Step-by-Step Solution:

1. **Understanding Infertility**:
- Infertility is defined as the inability to produce a viable offspring. This can occur in both males and females. In the context of males, it often relates to sperm quality and quantity.

2. **Sperm Count Analysis**:
- Sperm count is a crucial factor in male fertility. A normal sperm count is typically considered to be around 15 million to over 200 million sperm per milliliter of semen.

3. **Evaluating the Options**:
- **Option 1**: A count of 120 million per ml of semen.
- This is within the normal range and would not indicate infertility.
- **Option 2**: Increased acrosomal activity.
- Increased acrosomal activity means the sperm are more capable of penetrating the egg's membrane, which is a positive sign for fertility.
- **Option 3**: Normal morphology.
- Normal morphology means the sperm have the correct shape and structure, which is also conducive to fertilization.
- **Option 4**: A count of less than 20 million per ml of semen.
- This is below the normal threshold and is considered a condition that can lead to infertility.

4. **Conclusion**:
- Based on the analysis, infertility could develop when the sperm cells display a count of less than 20 million per ml of semen. Therefore, the correct answer is **Option 4**.