Q.70 Match the terms given in Group I with the descriptions from Group II.
Group I
(P) Photoautotrophs
(Q) Chemoautotrophs
(R) Photoheterotrophs
(S) Chemoheterotrophs
Group II
(I) Use inorganic chemical reactions for energy production
(II) Use organic compounds for energy production
(III) Use sunlight as energy source and carbon dioxide as carbon source
(IV) Use sunlight as energy source and organic compounds as carbon source
(A) P-II, Q-I, R-IV, S-III
(B) P-III, Q-I, R-IV, S-II
(C) P-IV, Q-III, R-I, S-II
(D) P-II, Q-IV, R-III, S-I
Microorganisms rely on specific energy and carbon sources for growth, classified into photoautotrophs, chemoautotrophs, photoheterotrophs, and chemoheterotrophs. This article solves a common exam question matching these terms to their descriptions, identifies the correct answer (option B), and explains all options for clarity.
Correct Answer
The correct matching is (B) P-III, Q-I, R-IV, S-II.
Photoautotrophs (P) use sunlight for energy and CO₂ as carbon source (III).
Chemoautotrophs (Q) use inorganic chemical reactions for energy (I), typically with CO₂.
Photoheterotrophs (R) use sunlight for energy but organic compounds for carbon (IV).
Chemoheterotrophs (S) use organic compounds for both energy and carbon (II), like most animals and fungi.
Group I and II Definitions
Group I Terms:
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(P) Photoautotrophs: Light energy, inorganic carbon (e.g., plants, algae via photosynthesis).
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(Q) Chemoautotrophs: Chemical energy from inorganics (e.g., nitrifying bacteria oxidizing NH₃).
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(R) Photoheterotrophs: Light energy, organic carbon (e.g., purple non-sulfur bacteria).
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(S) Chemoheterotrophs: Chemical energy from organics (e.g., humans, E. coli).
Group II Descriptions:
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(I) Inorganic chemical reactions for energy.
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(II) Organic compounds for energy.
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(III) Sunlight energy, CO₂ carbon.
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(IV) Sunlight energy, organic carbon.
Why Option B is Correct
Option B perfectly aligns each term: P-III (photoautotrophs fix CO₂ using light), Q-I (chemoautotrophs oxidize inorganics), R-IV (photoheterotrophs need organics despite light), S-II (chemoheterotrophs metabolize organics). This reflects standard microbiology classifications based on energy (photo/chemo) and carbon (auto/hetero) sources.
Analysis of All Options
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(A) P-II, Q-I, R-IV, S-III: Wrong; photoautotrophs (P) do not use organics for energy (II), and chemoheterotrophs (S) do not use CO₂ (III).
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(B) P-III, Q-I, R-IV, S-II: Correct, as explained above.
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(C) P-IV, Q-III, R-I, S-II: Wrong; photoautotrophs (P) use CO₂, not organics (IV); chemoautotrophs (Q) use chemicals, not light (III).
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(D) P-II, Q-IV, R-III, S-I: Wrong; mismatches all—photoautotrophs avoid organics (II), chemoautotrophs avoid light (IV).
| Option | P Match | Q Match | R Match | S Match | Correct? |
|---|---|---|---|---|---|
| A | II | I | IV | III | No |
| B | III | I | IV | II | Yes |
| C | IV | III | I | II | No |
| D | II | IV | III | I | No |
Exam Preparation Tips
Understand “photo” (light), “chemo” (chemicals), “auto” (inorganic carbon like CO₂), “hetero” (organic carbon) to ace such questions. Practice with examples: cyanobacteria (photoautotrophs), Thiobacillus (chemoautotrophs), Rhodospirillum (photoheterotrophs), yeast (chemoheterotrophs).
