Question

A free-Living aerobic and non-photosynthetic nitrogen fixing bacterium is
A. Anabaena
B. Clostridium
C. Azotobacter
D. Rhizobium

Answer 1

Free-living bacteria are organisms that are capable of independent existence meaning they are not directly dependent upon other organisms for their survival. Non- photosynthetic nitrogen fixing bacteria are bacteria that are helpful in converting the nitrogen into ammonia so that plants can use them.

Complete answer:
Atmospheric nitrogen is not available to plants.
So, some bacteria are present in the environment that convert this atmospheric nitrogen into ammonia and which is then able to be used by the plants. This type of bacteria are known as Non photosynthetic nitrogen fixing bacteria.
For example: Klebsiella.

Aerobic bacteria are those that can live and grow in the presence of sufficient amounts of oxygen and are not dependent upon other organisms for their survival.

So, according to the question,
- Option 1 Anabaena: It is a free-living as well as symbiotic nitrogen fixing bacteria.
- Option 2 Clostridium: It is a free-living and anaerobic nitrogen fixing bacteria.
- Option 3 Azotobacter: They are free-living aerobic and non-photosynthetic nitrogen fixing bacteria.
- Option 4 Rhizobium: It is non free living symbiotic nitrogen fixing bacteria.

Hence, the correct answer is option (C).

Note: Nitrogen-fixing bacteria accomplish more than 90 percent of all nitrogen fixation and thus play an important role in the nitrogen cycle. Because of these bacteria, legumes have the nitrogen necessary to make lots of proteins which in turn is why beans are such a good source of dietary protein for humans and other animals. Moreover legumes and certain cereal grasses are often grown as green manures and for crop rotation on farms as an organic source of nitrogen for other crops.