Question

Select the correct statement regarding heterocyst
A) These are present in some filamentous cyanobacteria the as Nostoc and Anabaena
B) These cells are specialised ro perform N2 fixation.
C)These cells contain enzyme nitrogenase
D) All of the above

Answer 1

Hint:Heterocysts are used for nitrogen fixation during lack of nitrogen.These are the only cells that express nitrogen fixation.

Complete answer:
A differentiated cyanobacterial cell that carries out nitrogen fixation is called a heterocyst.
It functions as a site for nitrogen fixation under aerobic conditions. They are mainly formed in response to the lack of fixed nitrogen.
A mature heterocyst doesn't contain a photosystem II and perhaps cannot produce its own oxygen. With morphological differentiation, biochemical alterations also take place.
They only contain photosystem I which helps them to carry out cyclic photophosphorylation and ATP regeneration. The oxygen sensitive nitrogenase can function efficiently under these conditions.
Heterocyst fixes nitrogen from the dinitrogen present in air. This nitrogen is provided to the cells. They also upregulate the glycolytic enzyme. Oxygen scavenger proteins are also produced to create an environment for the efficient working of nitrogenase.
Heterocyst are mainly found in filamentous algae like Nostoc, Anabaena, Cylindrospermum etc.

Hence the correct answer is option (D.) All of the above.

Note:The cyanobacteria that have heterocysts are divided into the orders Nostocales and Stigonematales. They have very low genetic variability.