UPSC Prelims 2023 · GS Paper I
Question 18: Science and Technology
Consider the following statements :
- 1.Some microorganisms can grow in environments with temperature above the boiling point of water.
- 2.Some microorganisms can grow in environments with temperature below the freezing point of water.
- 3.Some microorganisms can grow in highly acidic environment with a pH below 3.
How many of the above statements are correct?
AnswerUPSC’s answer is (c).
All three are correct because extremophiles exist. Hyperthermophiles such as Pyrolobus fumarii grow above 100 degrees C near deep-sea hydrothermal vents, where pressure keeps water liquid. Psychrophiles grow below 0 degrees C in salty brine veins of sea ice and permafrost. Acidophiles such as Picrophilus species thrive at pH close to 0, far below pH 3.
- 1. Hyperthermophiles grow above 100 degrees C under pressure.
- 2. Psychrophiles grow below freezing in brine veins.
- 3. Acidophiles grow at pH below 3.
How you could have got this
No shortcut here: in a “how many” question, ruling out options doesn’t help. Every statement has to be judged.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) Only one would deny two true statements.
- (b) Only two would deny one true statement.
- (c) Correct: heat-loving, cold-loving and acid-loving microbes all exist.
- (d) Extremophiles are well documented, so not none.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2023, General Studies Paper I, Series A. The paper on upsc.gov.in.