Question

Which of the following is autotrophic bacteria?
A)Azolla
B)Azotobacter
C)Nostoc
D)Anabaena

Answer 1

An autotroph is an organism which using light, water, carbon dioxide, or other chemicals, can produce its own food. Autotrophic bacteria can synthesise their food from simple inorganic nutrients, whereas heterotrophic bacteria are nutritionally dependent on preformed foods.

Complete answer:
Bacteria may be categorised as autotrophic or heterotrophic, depending on the way they use the two basic resources for their survival, energy and carbon (which they use to synthesise organic substances). Autotrophic prokaryotes can synthesise organic molecules, including carbon dioxide, from inorganic molecules. Light or other chemicals may provide the energy necessary for the synthesis.

Autotrophic bacteria are classified into two kinds, based on the types of sources used. The two autotrophic bacteria of various kinds are:
Photosynthetic, or photoautotrophs. With sunlight, they derive electricity.
Chemosynthetic or Chemoautotrophs. To prepare their food, they use chemical energy.
Both forms of bacteria need a carbon source to synthesise their food, e.g. carbon dioxide and other compounds, in addition to energy requirements.
Some examples include:
1.Algae.
2.Cyanobacteria.
3.Maize plant.
4.Grass.
5.Wheat.
6.Seaweed.
7.Phytoplankton.

Azolla establishes a symbiotic relationship with a cyanobacterium that fixes nitrogen. Bacteria that are capable of carrying out photosynthesis are cyanobacteria.
This bacteria has the capacity to make their own food or prepare it.
They possess the pigment required for the photosynthesis process to be performed.
Anabaena bacteria are useful for fixing molecules of nitrogen in the atmosphere.
As it can conduct photosynthesis, Anabaena also acts as a producer at the trophic stage.
In both marine as well as terrestrial ecosystems or habitats, they are found.

Hence, the correct answer is option (D)
Note: Autotrophs will have to be the first life forms on Earth in order to survive and make energy and biological materials in a previously non-living world. When autotrophs became more widespread, heterotrophs more likely evolved, and some life forms realised that merely consuming the autotrophs was simpler than producing energy and organic materials for themselves.