Nostoc and Anabaena have specialised cells called heterocysts. What is the function of these cells?

Explanation

### Step-by-Step Solution

1. **Identify the Organisms**: Nostoc and Anabaena are both types of cyanobacteria, which are photosynthetic bacteria.

2. **Understand the Role of Heterocysts**: Heterocysts are specialized cells found in Nostoc and Anabaena.

3. **Function of Heterocysts**: The primary function of heterocysts is to fix nitrogen. They contain the enzyme nitrogenase, which is crucial for the conversion of atmospheric nitrogen (N2) into ammonia (NH3), a form that plants can utilize.

...