Fertility of soil is Increased by-

Options

A. Nitrogen - fixing bacteria
B. Denitrifying bacteria
C. Plasmalemma
D. Cellmembrane

Answer

To answer the question "Fertility of soil is increased by?", we can follow these steps:

### 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 plant growth and agricultural productivity.

2. **Identifying Key Factors**: Among the options provided, we need to identify which factors contribute to increasing soil fertility. The options are:
- Nitrogen fixing bacteria
- Denitrifying bacteria
- Plasma lemma
- Cell membrane

3. **Evaluating Nitrogen Fixing Bacteria**:
- Nitrogen fixing bacteria are microorganisms that convert atmospheric nitrogen (N2) into ammonia (NH3) through a process known as nitrogen fixation.
- This process is essential because plants cannot utilize atmospheric nitrogen directly. Instead, they require nitrogen in a form they can absorb, such as nitrates.

4. **Understanding the Nitrogen Cycle**:
- After nitrogen fixation, ammonia is further processed through nitrification, where it is converted into nitrites (NO2-) and then into nitrates (NO3-).
- Nitrates are readily absorbed by plants, thus enhancing soil fertility.

5. **Evaluating Other Options**:
- **Denitrifying Bacteria**: These bacteria convert nitrates back into nitrogen gas, which decreases soil fertility as it removes usable nitrogen from the soil.
- **Plasma Lemma and Cell Membrane**: These terms refer to cellular structures and do not have any direct role in enhancing soil fertility.

6. **Conclusion**: Based on the evaluation, the correct answer is that soil fertility is increased by **Nitrogen fixing bacteria**.

### Final Answer:
Soil fertility is increased by **Nitrogen fixing bacteria**.

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