Question

Nitrogen fixation by Nostoc / Anabaena takes place in
A) Heterocyst
B) Vegetative cells
C) Akinetes
D) Hormogonia

Answer 1

Hint: Ammonia is a colourless gas that is composed of nitrogen and hydrogen atoms. It is formed naturally in us but in soil and in the environment when nitrogen gets reduced there are nitrogen fixers that convert nitrogen to ammonia.

Complete Answer:
To solve this question, we have to know details about nitrogen fixation.
Nitrogen fixation is the process of converting nitrogen found in the atmosphere into ammonia. This process is maintained by organisms like Nostoc and Anabaena, they are considered as the nitrogen fixing bacteria.
Both of these bacteria show a symbiotic association with some of the plants like mosquito fern.
In Anabaena, when there is a decrease in the amount of nitrogen in the soil the vegetative cells differentiated into heterocyst, this cell is formed for the nitrogen fixation process.
It increases the respiration process as the inner surface of the cell is micro-oxic thus involved in the inactivation of the oxygen production in photosystem II and forms a thick outer cell wall.
Nitrogenase, the enzyme required for the conversion of nitrogen to ammonia is found within the heterocyst.
During the process of photosystem I the plant produces carbohydrates in the form of glucose, this moves inside the heterocysts and in return it maintains the nitrogen fixation and gives this back to the plant.
Anabaena forms a symbiotic association with the fern Azolla and is named Anabaena Azollae. This involves the nitrogen fixation process and in return it provides the plant essential nutrients.

Hence, the correct answer is ‘A’ Heterocyst.

Note: This process of nitrogen fixation is also used for the production of synthetic fertilizers, in which nitrogen in presence of nitrogenase is converted to ammonia. Beside this there is one more way in which nitrogen fixation takes place, that is during lightning atmospheric nitrogen is converted to ammonia.