Question

Which one is a nitrogen fixer blue green algae?
A. Ulothrix
B. Anabaena
C. Ulva
D. Hydrodictyon

Answer 1

Hint: Blue green algae are a type of prokaryote, which is also known as cyanobacteria. Among blue green algae, some of them are nitrogen fixing bacterias, which means they are microorganisms that can transform atmospheric nitrogen into fixed nitrogen that can be utilized by plants.

Complete Answer:
Before looking through the options, let's understand some details about blue green algae.
- Blue green algae, also known as cyanobacteria are a type of photosynthetic bacteria, which are seen as single celled or exist as colonies. Green pigment called chlorophyll a is present in blue green algae.
- Natural habitats of blue green algae are marine and freshwater systems. They have been called blue green algae, because they normally look green and gradually turn blue at the time of their death. Most of the species show buoyancy and they float on the surface of the water.
- Blue green algae are some of the major microbes which fix nitrogen in fields, thereby helping in food production. The process of converting atmospheric nitrogen into combined compounds like ammonia, nitrate, nitrite etc. is known as nitrogen fixation.

Now, let's have a look through the options for finding the correct answer.
Option A: Ulothrix is a filamentous green algae, which are mostly seen in fresh and marine waters. But, they don't help in nitrogen fixation. Therefore, this is the incorrect option.
Option B: Anabaena is a type of blue green algae, with barrel like cells. They help in nitrogen fixation in paddy fields. Therefore, this is the correct option.
Option C: Ulva, also known as sea lettuce, is an edible green algae, which are widely seen in ocean coasts. But, they don't help in nitrogen fixation. Therefore, this is the incorrect option.
Option D: Hydrodictyon, which is also known as a water net, is a freshwater green algae with mesh like colonies. But, they are not nitrogen fixing bacterias. Therefore, this is the incorrect option.

Thus, the correct option is B) Anabaena.

Note: Anabaena, the nitrogen fixing blue green algae, forms a nitrogen fixing symbiosis with Azolla, and they fix nitrogen in the presence of significant amounts of oxygen. The Azolla-Anabaena combination is also regarded as "green gold mine", since they are capable of fixing atmospheric nitrogen at high rates, and helps in the wet-rice cultivation.