Some of the Cyanobacteria can fix atmospheric nitrogen in specialised cells called-

Options

A. Akinetes
B. Heterocyst
C. Homocyst
D. Nodule

Answer

To answer the question about which specialized cells in some cyanobacteria can fix atmospheric nitrogen, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Organism**: The question refers to cyanobacteria, which are a group of photosynthetic bacteria known for their ability to perform nitrogen fixation.

2. **Understand Nitrogen Fixation**: Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia (NH₃), a form that can be utilized by living organisms.

3. **Specialized Cells in Cyanobacteria**: Some cyanobacteria have specialized cells that are specifically adapted for nitrogen fixation.

4. **Know the Options**: The options provided are:
- A) Echinids
- B) Heterocyst
- C) Homocyst
- D) Nodules

5. **Eliminate Incorrect Options**:
- **Echinids**: This term refers to a group of marine animals (like sea urchins) and is not related to cyanobacteria.
- **Homocyst**: This term does not pertain to any known specialized cell in cyanobacteria.
- **Nodules**: These are structures found in some plants (like legumes) where nitrogen-fixing bacteria reside, but they are not specific to cyanobacteria.

6. **Correct Answer**: The specialized cells in cyanobacteria that fix nitrogen are called **Heterocysts**. They contain the enzyme nitrogenase, which is crucial for the nitrogen fixation process. Heterocysts are adapted to provide an anaerobic environment, as nitrogenase is inactivated by oxygen.

### Final Answer:
The specialized cells in some cyanobacteria that can fix atmospheric nitrogen are called **Heterocyst**.

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