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General ScienceEasyAsked in: CDS · CDS-II 2026, GK

Which one of the following is involved in light independent reactions of photosynthesis?

  1. A.Calvin cycle
  2. B.Hill reaction
  3. C.Photosystem
  4. D.Light absorption by photosynthetic pigments

Correct answer

A. Calvin cycle

Explanation

The correct answer is A, Calvin cycle. The Calvin cycle fixes carbon dioxide into sugar without needing light directly, so it forms the light-independent (dark) reactions.

Photosynthesis happens in two stages inside the chloroplast. The light reactions take place on the thylakoid membranes: pigments absorb light, water is split, oxygen is released and ATP and NADPH are made. The light-independent reactions take place in the stroma, where the enzyme RuBisCO joins carbon dioxide to ribulose bisphosphate and the ATP and NADPH from the first stage are used to build glucose. Melvin Calvin worked out this cycle and won the 1961 Nobel Prize in Chemistry for it.

Option B is wrong because the Hill reaction, the light-driven splitting of water that releases oxygen, is part of the light reactions. Option C is wrong because photosystems I and II capture light energy. Option D is wrong because absorption of light by chlorophyll is the very first light-dependent step.

Exam tip: light reactions = thylakoid, give ATP, NADPH and O2; Calvin cycle = stroma, makes sugar from CO2.

Practice Questions

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Q1.General ScienceAsked in: CDS · CDS-II 2020, GKEasy

The valency of phosphorus is

  1. A.2, 3
  2. B.3, 4
  3. C.4, 5
  4. D.3, 5
Show answer
Correct answer: D. 3, 5

Phosphorus has five electrons in its outer shell and shows two common valencies, 3 and 5. Phosphorus, atomic number 15, has the electronic configuration 2, 8, 5.

Q2.General ScienceAsked in: CDS · CDS-II 2026, GKMedium

Which one of the following statements is NOT correct ?

  1. A.Single celled eukaryotes belong to Kingdom Protista
  2. B.Yeast, a fungus is multicellular
  3. C.The fungi constitute a unique kingdom of heterotrophs
  4. D.Ascomycetes, a saprophytic fungi is multicellular or rarely unicellular
Show answer
Correct answer: B. Yeast, a fungus is multicellular

This statement is false, because yeast is one of the few fungi that are unicellular. In Whittaker's five-kingdom system, fungi form a separate kingdom.

Q3.General ScienceAsked in: CDS · CDS-II 2017, GKMedium

Desalination of seawater is done by using reverse osmosis. The pressure applied to the solution is

  1. A.larger than osmotic pressure
  2. B.smaller than osmotic pressure
  3. C.equal to osmotic pressure
  4. D.equal to atmospheric pressure
Show answer
Correct answer: A. larger than osmotic pressure

Only a pressure greater than the osmotic pressure of seawater can push pure water backwards through the membrane. In ordinary osmosis, water moves through a semipermeable membrane from the dilute side to the concentrated side.

Q5.General ScienceAsked in: CDS · CDS-II 2017, GKEasy

The foul smell of urine of a healthy man having healthy food, when spilled on floor, is mainly due to the bacterial decomposition of

  1. A.urea into sulphur dioxide
  2. B.sugar into carbon dioxide
  3. C.lipids into methane
  4. D.urea into ammonia
Show answer
Correct answer: D. urea into ammonia

Bacteria on the floor break down the urea in urine and release ammonia, which has a sharp, pungent smell. Urea, CO(NH2)2, is the main nitrogenous waste of humans.