Question

The first organisms on primitive earth were
A. Autotrophic
B. Heterotrophic and Anaerobic
C. Parasitic
D. Prokaryotic and Autotrophic

Answer 1

Hint: The process of abiogenesis or the origin of life is the natural way of formation of life. It occurred from non-living matter such as simple organic compounds. According to the scientific hypothesis, the formation of living entities from non-living is not a single event rather it is a sequential evolutionary process of increasing complexity.

Complete answer:
In the primitive earth life was formed from the non-living matter such as simple organic compounds. Life on the primitive earth is based on carbon and water. This carbon gives a stable structure for complex chemicals and can be easily turned out of the environment, especially from carbon dioxide.
Bacteria like the prokaryotic cell were the very first organisms that arise on Earth. They appeared in the primitive earth three billion years ago and first appeared in the waters of the oceans. They have originated from protocells in the Archaeozoic era; this is an era of 3800 million years ago.
In the beginning, there were only anaerobic heterotrophic bacteria. The first life that arises on the earth was anaerobic because the atmosphere of early earth was reducing and oxygen was present there.
These bacteria were chemoheterotrophs and they used the organic component as a source of energy and carbon. As there the supply of organic compounds was limited and later on the organisms adopted photosystems to capture sunlight which is used as a source of energy. These results in the origin of photoautotrophs.
The organisms for which the source of energy is light and the source of chief carbon is the carbon dioxide, they are known as photoautotrophic organisms. These organisms take water as a donor of the electron at the time of photophosphorylation which leads to the production of oxygen. The collection of oxygen in the atmosphere further leads the origin to aerobic forms and these forms were more efficient in energy production as compared to their ancestral anaerobic forms.

Therefore, the correct option is option B.

Note: The primitive earth or early earth refers to the earth after its formation in the solar system. After several years of transformation, the environment becomes favourable for the origin of life. Bacteria were the very first organisms to originate as life on the earth. As in the primitive earth, the oxygen was limited, there were only anaerobic heterotrophic bacteria.