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General Studies 2022 GS Paper III 10 marks 150 words Compulsory Describe

GS Paper III — Q6

Each year a large amount of plant material, cellulose, is deposited on the surface of Planet Earth. What are the natural…

Each year a large amount of plant material, cellulose, is deposited on the surface of Planet Earth. What are the natural processes this cellulose undergoes before yielding carbon dioxide, water and other end products? (Answer in 150 words) 10 marks

हिंदी में प्रश्न पढ़ें

पृथ्वी की सतह पर प्रति वर्ष बड़ी मात्रा में वनस्पति पदार्थ, सेलुलोस, जमा हो जाता है। यह सेलुलोस किन प्राकृतिक प्रक्रियाओं से गुजरता है जिससे कि वह कार्बन डाइऑक्साइड, जल तथा अन्य अंत उत्पादों में परिवर्तित हो जाता है? (150 शब्दों में उत्तर दीजिए)

Q6 of the 2022 UPSC Mains General Studies GS Paper III, as printed
The question as printed in the 2022 General Studies paper
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Model answer

Written by UPSC Answer Check against this question's marking rubric, to the 150-word length. UPSC does not publish answers for Mains — this is one way to score well, not an official key.

Cellulose, Earth’s most abundant biopolymer, is transformed by coupled biological, chemical and thermal processes. In soils, cellulase-producing bacteria such as Cellulomonas and fungi like Trichoderma hydrolyse glycosidic bonds, yielding cellobiose and glucose. Aerobic decomposers oxidise these sugars through glycolysis, the Krebs cycle and the electron transport chain, releasing CO₂, water and heat. In oxygen-poor wetlands, paddy fields and rumen, after hydrolysis, fermentative bacteria convert sugars to organic acids, H₂ and CO₂; methanogenic archaea then use acetate, H₂ and CO₂ to form methane and CO₂. Partially degraded material forms humus and lignin-cellulose complexes, while in peatlands such as the Sundarbans, slow decomposition sequesters carbon; in warm tropical soils, mineralisation is rapid. Abiotic routes include photochemical oxidation, forest-fire combustion and slow thermal degradation, ultimately returning carbon to the atmosphere. Thus, cellulose cycling links plant litter, soil organic matter and atmospheric carbon, regulating climate and soil fertility in terrestrial ecosystems over seasonal cycles.

What "Describe" is asking you to do

Give a full, ordered account of the thing named — its parts, stages or mechanism — in the sequence in which it actually exists or occurs. Most describe questions come from the science optionals, where the marks sit in correct technical detail and, where the stem says so, a labelled diagram.

Structure that answers it

One-line identification of the subject → the parts or stages in their real order, each with its defining detail → labelled diagram where the subject is structural → closing line on function or significance

Where marks are lost

Loose general prose where the examiner is ticking named parts, correct terminology and their sequence; and in the General Studies papers, turning to evaluation before the description is finished.

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How this answer will be evaluated

Approach

Framework: Environment: threat, causes, impact, mitigation. trace: start point > the stages in sequence > end point > what changed Full marks: Clear sequence from cellulose to CO2/water with specific biological agents

Key points expected

  • Identifies cellulose as the primary substrate
  • Describes microbial enzymatic breakdown (cellulase)
  • Distinguishes aerobic vs anaerobic pathways
  • Links process to carbon cycle

Evaluation rubric

Each sub-part is marked on its own, against the marks and word limit printed on the paper.

  1. The answer Sequence of natural processes converting cellulose to CO2, water, and other products 10 marks · 150 words

    trace— start point → the stages in sequence → end point → what changed

    Must cover

    • Identifies cellulose as the primary substrate
    • Describes microbial enzymatic breakdown (cellulase)
    • Distinguishes aerobic vs anaerobic pathways
    • Links process to carbon cycle

    Loses marks

    • Confusing photosynthesis with decomposition
    • Vague description without specific processes
    • Ignoring the 'natural' constraint (focusing on industrial)

    Earns more

    • Mention of specific decomposers (bacteria/fungi)
    • Reference to intermediate products (glucose, acids)
    • Context of soil or aquatic environment
    • Mention of methane as an end product

    Extra mark

    • Simple flowchart of the decomposition pathway
    • Specific enzyme names (e.g., endoglucanase)

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Write your answer and it is marked point by point against the model answer above — what you covered, what you missed, what you got wrong.

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