Question

Cyanobacteria (Nostoc) is:
A) Oxygenic with nitrogenase.
B) Oxygenic without nitrogenase.
C) Non-oxygenic with nitrogenase.
D) Non-oxygenic without nitrogenase.

Answer 1

They are aquatic bacteria; they are some of the oldest living organelles on earth. They appear in many different colours. They can be found in many different environments, including freshwater and marine systems.

Complete Answer:
- Cyanobacteria is a phylum consisting of both free-living photosynthetic bacteria and the endosymbiotic plastids. They obtain energy through oxygenic photosynthesis.
- The oxygen gas in the atmosphere of the earth is produced by cyanobacteria of this phylum, either as free-living bacteria or as endosymbiotic plastids. They are also called blue green algae. They originated from freshwater or a terrestrial environment.
- There are a number of human activities that increase the level of nutrients present in the body especially, nitrogen which is an energy source for growth of the bacteria.
- Nitrogen source affects the waterways that include agricultural residential and urban run-off. Cyanobacteria also contain chlorophyll and it is the same photosynthetic pigment that is used by the plant.
- They are the organism that converts inert atmospheric nitrogen into an organic form like ammonia or nitrate.
- They contain additional nitrogen that plants can obtain through their roots. Nitrogen is fixed in the specialised cells of the cyanobacteria which are called heterocyst.

Thus, the correct answer is option A. i.e., oxygenic with nitrogenase.

Note: Cyanobacteria are microscopic and rich in chemical diversity and they use photosynthesis to make their own food in the presence of oxygen so they are oxygenic. They are also nitrogenase as they convert inert atmospheric nitrogen into nitrate or ammonia.