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GATE 2025 BT – Question 36

General Biology · Microbiology: Microbial growth and nutrition, operons (lac, trp, ara), nitrogen fixation · 2 marks · Multiple choice

Correctly match the Microorganisms with their respective Nutrition and energy requirement.

MicroorganismsNutrition and energy requirement
P. Photolithoautotrophs1. Use organic compounds as a source of energy, hydrogen, electron and carbon
Q. Chemoorganoheterotrophs2. Use light energy and use CO$_2$ as their carbon source
R. Chemolithoautotrophs3. Use light energy and use organic compounds as electron donor and carbon source
S. Photoorganoheterotrophs4. Oxidise reduced-inorganic molecules as energy and electron source but derive carbon from organic sources
  1. P-2; Q-1; R-4; S-3
  2. P-2; Q-1; R-3; S-4
  3. P-1; Q-2; R-4; S-3
  4. P-4; Q-1; R-2; S-3

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Correct answer: (A) P-2; Q-1; R-4; S-3

Explanation

Photolithoautotrophs use light and $CO_2$ (2). Chemoorganoheterotrophs use organic compounds for energy, electrons and carbon (1). Photoorganoheterotrophs use light with organic compounds as electron donor and carbon source (3). That leaves 4 for the chemolithotrophs, which oxidise inorganic molecules for energy (the description in the paper says organic carbon, which fits only a chemolithoheterotroph, but it is the only one left).

Official GATE 2025 answer key: https://gate2026.iitg.ac.in/doc/download/2025_Key/BT_Keys.pdf