Question

Heterocyst is a structure which is associated with
A. Reproduction
B. Respiration
C. Nitrogen fixation
D. Locomotion

Answer 1

Hint: Heterocyst is a structure found in many species of filamentous blue-green algae. These cells are larger and are having more thickened walls as compared to the vegetative cells. These cells are produced in BGA by vegetative cells during the condition of starvation of certain elements.

Complete answer: Heterocyst is the specialized nitrogen-fixing cell found in cyanobacteria or blue-green algae. These are formed by blue-green algae during the condition of nitrogen deficiency. Some of the examples are Nostoc punctiforme, Cylindrospermum stagnale, and Anabaena sphaerica. Heterocyst fixes nitrogen from dinitrogen in the air with the help of enzymes nitrogenase. It creates a micro anaerobic environment. This is done to provide the nitrogen needed for biosynthesis to the cells in the filament. Heterocyst has a thick wall with three additional wall layers and is developed from vegetative cells and also having one or more pores. Heterocyst is also an active site for the synthesis of protein. Also, the reproductive structures in blue-green algae are conidia, exospores, endospores, akinete but not heterocyst. Heterocyst is not involved in the respiration as it generates ATP without photolysis. Locomotion in BGA involves gliding.
Hence, the correct answer to the above question is option C, i.e., Nitrogen fixation.

Note: Heterocyst is the thick-walled structure produced from vegetative cells. They are present in blue-green algae and are required at the time of nitrogen deficiency by fixing nitrogen from the dinitrogen in the air. The enzyme is used in nitrogen fixation in nitrogenase. They are also involved in protein synthesis.