Question

First life form on earth was a
A. Cyanobacterium
B. Chemoheterotroph
C. Autotroph
D. Photoautotroph

Answer 1

Hint: Organisms on Earth initially arose 4.28 billion years ago. Life on this planet has transformed its ecosystem on a geological time scale, but it has also adjusted to function in several habitats and conditions. Some ideas of the existence of life are being suggested, but just because it's impossible to determine or disprove them, there seems to be no firmly accepted theory.

Complete answer:
It is claimed that the very first life forms are chemoheterotrophs which derived energy from the metabolism of complex organic compounds available to them through the seafloor. They were anaerobic. Chemo-synthesis is accomplished by chemo-heterotrophs by the oxidation of electron donors in the atmosphere.

Chemo-heterotrophs are identified in seafloors where sunlight cannot penetrate them because of considerable length and then all the layers of water among them and the sun. They have adapted so that it is not dependent on solar energy. Ocean floors frequently involve submerged volcanic eruptions that could provide heat as a substitution for the warmth of sunlight.

Chemo-heterotrophs are indeed capable of surviving in habitats that really are sufficient to support other forms of life due to dependence on carbon sources for such species. Chemo heterotrophs are by far the most dominant chemotrophic species which include many bacteria, fungi, and protozoa. Chemo-heterotrophs cannot use carbon to produce their own organic molecules. Rather, their carbon source is formed from sulphur, sugars, lipids, and proteins

So, the correct answer is option (B).

Additional information:
Chemoautotrophs are capable of producing their own organic compounds with carbon fixation. These beings are capable of creating their respective food or energy supply. Chemoautotrophs are likely to exist in very extreme conditions, including deep-sea vents, owing to a lack of emphasis on non-carbon supplies apart from carbon dioxide. Many microbes too are chemoheterotrophs, like other bacteria living within the human body, some infectious bacteria, and also some sulphur bacteria. Chemoheterotrophs strip resources from plants and chemoautotrophs as well as reuse them in such a dynamic network of life, whereby substances are being used again and again.

Note: E. coli seems to be a chemoheterotroph capable of producing any of various sugars or amino acids administered separately or in blends. Halophilic archaea are basically aerobic chemoheterotrophs during favourable conditions to life. Whereas when exposed to certain conditions, different modes of energy production and anaerobic growth could be seen in the lack of air.