Question

Some blue green algae are used as biofertilizers because they
A. Are photosynthetic
B. Have mucilage
C. Grow everywhere
D. Fix nitrogen

Answer 1

Hint: The biofertilizers are the microbes or bacteria which help in promoting the growth and development of plants and trees by supplying essential amounts of nutrients. In addition, fertilizers have a high concentration of nitrogen.

Complete answer: Cyanobacteria commonly referred to as blue green algae derive its name from its color. These are photosynthetic bacteria with the ability to fix nitrogen. Atmospheric nitrogen is fixed in aerobic conditions by means of specialized cells called heterocyst by means of cyanobacteria. These bacteria can fix nitrogen gas into ammonia, nitrates, and nitrites which can be absorbed by plants to convert into proteins and nucleic acid. In some plants, atmospheric nitrogen is not readily available and hence blue green algae are used as biofertilizers for nitrogen fixing except for the plants that have endosymbiotic nitrogen fixing bacteria. It can be used as a biofertilizer in rice fields. Some of the examples of blue green algae are Anabaena and Nostoc.
As it is used for fixing atmospheric nitrogen in plants with the absence of endosymbiotic bacteria, it is referred to as a biofertilizer which helps plants to make use of ammonia for its growth and development.
Additional information: The blue color extracted from spirulina is used as a natural food coloring in gum and candy. Neurotoxin, cytotoxin, endotoxin, and hepatotoxin all collectively called cyanotoxin can be produced by cyanobacteria.

Note: The blue green algae/cyanobacteria are photosynthetic bacteria, but the reason for using it as biofertilizer is its ability to convert atmospheric nitrogen into ammonia that is the fixation of nitrogen in plants and trees.