Question

The present day organisms dominant in the primitive reducing atmosphere are:

• A. Cyanobacteria
• B. Methanobacteria
• C. Red algae
• D. Brown algae

Answer 1

The correct option is B Methanobacteria

The primitive atmosphere of earth was reducing atmosphere with little or no oxygen. Methanogens are anaerobic autotrophic eurkaryotes that convert carbon dioxide and hydrogen into methane gas.

Hydrogen serves as electron donor for reduction of carbon dioxide. This makes option B correct.

Methanobacteria are now found in gut of cattle, depth of landfills, salt marshes where oxygen is not available.

Cyanobacteria are aerobic photoautotrophic bacteria that fix atmospheric carbon dioxide into organic compound by oxygenic photosynthesis and exhibit aerobic respiration.

Red algae (Rhodophyta) and brown algae (Phaeophyta) are also photoautotrophic aerobic organisms that exhibit aerobic respiration to produce higher amount of ATPs. Since, oxygen was absent in primitive atmosphere, aerobic organisms were absent at the time which makes options A, C and D incorrect.

Therefore, the correct answer is option B.