Feritlity of soil is increase by

Options

A. Nitrogen - fixing bacteria
B. Denitrifying bacteria
C. Plasmalemma
D. Cell membrane

Answer

### Step-by-Step Solution:

1. **Understanding Soil Fertility**: Soil fertility refers to the ability of soil to provide essential nutrients to plants. It is crucial for healthy plant growth and agricultural productivity.

2. **Identifying Factors that Increase Soil Fertility**: Various organisms and processes contribute to soil fertility. Among these, certain bacteria play a significant role in enhancing soil nutrient content.

3. **Examining the Options**:
- **Nitrogen Fixing Bacteria**: These bacteria convert atmospheric nitrogen (which is inert and not usable by plants) into ammonia, a form that plants can absorb and utilize. This process enriches the soil with nitrogen, a vital nutrient for plant growth.
- **Denitrifying Bacteria**: These bacteria convert nitrates in the soil back into nitrogen gas, which can decrease soil fertility by removing nitrogen that plants could use.
- **Plasma Lemma and Cell Membrane**: These terms refer to cellular structures and do not directly relate to soil fertility.

4. **Conclusion**: Based on the roles of the different types of bacteria, nitrogen-fixing bacteria are the ones that increase soil fertility by adding nitrogen to the soil, making it more fertile and suitable for plant growth.

5. **Correct Answer**: The correct option is **Nitrogen Fixing Bacteria**.