Photoautotrophs
Heterocysts are specialised cells that are borne by photoautotrophs. These cells play a crucial role in nitrogen fixation, a process that converts atmospheric nitrogen into a form that can be used by the organism for growth and development.

Function of Heterocysts
Heterocysts are responsible for the conversion of atmospheric nitrogen into ammonia through the process of nitrogen fixation. This ammonia can then be used by the organism for protein synthesis and other essential metabolic processes. Heterocysts provide a protective environment for the nitrogenase enzyme, which is sensitive to oxygen and needs an anaerobic environment to function effectively.

Significance of Heterocysts in Photoautotrophs
Heterocysts are essential for the survival and growth of photoautotrophs in environments where nitrogen is limited. By fixing atmospheric nitrogen into a usable form, heterocysts ensure that the organism has an adequate supply of this essential nutrient for its metabolic processes. This ability to perform nitrogen fixation gives photoautotrophs a competitive advantage in nitrogen-poor environments compared to other organisms that rely on external sources of nitrogen.

Conclusion
In conclusion, heterocysts are specialised cells borne by photoautotrophs that play a crucial role in nitrogen fixation. By converting atmospheric nitrogen into ammonia, heterocysts provide photoautotrophs with a vital source of nitrogen for their growth and metabolic processes, allowing them to thrive in nitrogen-limited environments.