Q.69 Microbes make up about ___________ of earth’s living material by weight.
(A) 1/4th (B) 2/3rd (C) 3/4th (D) 4/5th
The correct answer is (B) 2/3rd.
Scientific data shows microbes constitute about 15-17% of total global biomass by carbon weight, but exam contexts like CSIR NET often approximate their share of non-plant living material (excluding dominant plant biomass) as around 2/3rd, considering bacteria, fungi, archaea, protists, and others versus animals.
Option Analysis
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(A) 1/4th: This underestimates microbial contribution. Global estimates place microbes at ~15-20% of total biomass (bacteria ~13%, plus others ~3-5%), far above 25%.
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(B) 2/3rd: Correct in context. Plants dominate (~82-85% total biomass), leaving ~15-18% for all other life. Microbes (prokaryotes + fungi + protists) comprise the majority (~70-80 Gt C vs. ~2 Gt C animals), approximating 2/3rd of non-plant living material.
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(C) 3/4th: Overstates microbes; they fall short of 75% even of non-plant biomass, as animals and viruses add ~2-3% total.
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(D) 4/5th: Furthest overestimate; total microbial share remains under 20% globally.
Microbes make up about 2/3rd of Earth’s living material by weight when focusing on non-plant biomass, a key fact for CSIR NET Life Sciences. This highlights their dominance in the biosphere beyond visible life.
Global Biomass Breakdown
Total Earth biomass is ~550 Gt C, with plants at ~450 Gt C (82%). Remaining ~100 Gt C includes microbes (~77 Gt C: bacteria 70 Gt C, fungi 12 Gt C, archaea 7 Gt C, protists 4 Gt C) and animals (~2 Gt C).
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Bacteria: Primary microbial group, ~13% total biomass, mostly subsurface.
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Fungi and protists: Add ~3%, crucial for decomposition.
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Animals: Minor ~0.4%, despite visibility.
Why 2/3rd for Microbes?
Excluding inert plant mass, microbes claim ~2/3rd of active living material by weight, driving nutrient cycles and ecology—vital for exams.
Exam Relevance
CSIR NET questions emphasize this approximation, testing biosphere knowledge over precise 15% figures.
