Question

In blue green algae which structure specialized aerobic fixation

Answer 1

Blue-green algae or Cyanobacteria are a group of Gram –ve monerans that are capable of fixing atmospheric N2 into the soil. Heterocysts are specialised thick wall cells in BGA that serve this function.

Based on the presence or absence of heterocysts, cyanobactreia can be divided into two groups:-

1. Heterocystous bacteria:

These blue-green algae contain heterocysts which in turn contain an enzyme ‘nitrogenase’ which is sensitive to presence of oxygen. It is inactivated in the presence of oxygen. To help prevent inactivation of nitrogenase, these heterocystous bacteria don not contain PS II as it liberates oxygen during functioning. They contain only PS I. Since O2 is not liberated in the heterocysts, the nitrogen fixation occurs smoothly.

 

2. Non- heterocystous blue-green algae:

These bacteria they lack heterocysts. There vegetative cells however contain ‘nitrogenase’ enzyme. Also, they contain both the photosystems, PS I and PS II.

Even though O2 is liberated by PS II, it is quickly trapped in molecular respiration thereby not affecting the nitrogenase enzyme. They also secrete thick mucilage which stops the entry of O2. This is how the aerobic blue- green algae also conduct the nitrogen fixation. 

Hope this helps!

Answer 2

In blue green algae heterocytes structure specialized aerobic fixation.

The heterocysts function as the sites for nitrogen fixation under aerobic conditions. They are formed in response to a lack of fixed nitrogen (NH4 or NO3). The morphological differentiation is accompanied by biochemical alterations. The mature heterocysts contain no functional photosystem II and cannot produce oxygen.