UPSC Prelims 2012 Q63: Science & Technology – Biology
Which one of the following sets of elements was primarily responsible for the origin of life
on the Earth?
- (a) Hydrogen, Oxygen, Sodium
- (b) Carbon, Hydrogen, Nitrogen
- (c) Oxygen, Calcium, Phosphorus
- (d) Carbon, Hydrogen, Potassium
Answer: (b) Carbon, Hydrogen, Nitrogen
Explanation
Elements behind the origin of life
The early atmosphere had methane, ammonia, hydrogen and water vapour.
These are made of carbon, hydrogen, nitrogen and oxygen.
They combined to form amino acids, the building blocks of proteins.
| Option | Verdict | Reason |
|---|---|---|
| (a) Hydrogen, Oxygen, Sodium | Incorrect | Sodium is not a building block of organic molecules |
| (b) Carbon, Hydrogen, Nitrogen | Correct | All three are in amino acids and nucleic acids |
| (c) Oxygen, Calcium, Phosphorus | Incorrect | Calcium matters for bones, not for the first molecules of life |
| (d) Carbon, Hydrogen, Potassium | Incorrect | Potassium is not part of the basic organic molecules |
The Miller-Urey experiment (1953):
| Point | Detail |
|---|---|
| Gases used | Methane, ammonia, hydrogen and water vapour |
| Energy | Electric sparks, like lightning |
| Result | Amino acids formed |
| Supports | The Oparin-Haldane theory of chemical evolution |
Answer: (b) Carbon, Hydrogen, Nitrogen.
Why each option is right or wrong
- (a) Incorrect. Sodium played no primary part in forming the first organic molecules.
- (b) CORRECT. Carbon, hydrogen and nitrogen built the first amino acids.
- (c) Incorrect. Calcium was not primarily responsible for the origin of life.
- (d) Incorrect. Potassium is a mineral ion, not a basic element of organic molecules.
Key point
Origin of life: methane, ammonia, hydrogen and water formed amino acids (Miller-Urey, 1953; Oparin-Haldane theory). Core elements: carbon, hydrogen, nitrogen, oxygen.
Remember
Life began with carbon, hydrogen, nitrogen (and oxygen).
Common mistakes
- Choosing a set with oxygen first; the early atmosphere had no free oxygen.
- Forgetting that nitrogen is needed for amino acids.
- Picking metals such as sodium or potassium, which are not in the basic molecules of life.
Exam tip
Life is organic chemistry, so carbon must be there. Then pick the set with no metal in it.
Sources
- NCERT Class XII — Biology, Ch 7 (Evolution: Origin of Life)
- NCERT Class XI — Fundamentals of Physical Geography, Ch 2 (The Origin and Evolution of the Earth)