Question

Which of the following statements correctly describes the light reactions and dark reactions taking place during photosynthesis?
(i) Light reactions occur in grana thylakoids whereas dark reactions occur in stroma of chloroplasts.
(ii) Light reactions generate ATP and $NADP{H}_2$ whereas dark reactions consume ATP and $NADP{H}_2$.
(iii) Oxygen is released as a by-product during the light reactions as well as dark reactions.
(iv) Light reactions take place in the presence of light and dark reactions are independent of the products formed during light reactions.

• A. (i) and (ii)
• B. (iii) and (iv)
• C. (i), (ii) and (iv)
• D. (ii), (iii) and (iv)

Answer 1

Answer: (A)

(i) and (ii)

Photosynthesis consists of a set of light and dark reactions. In the light reactions, the energy from sunlight is utilized in the photochemical reduction of $H_{2}O$ so that oxidizing agent $NAD{P}^{+}$ is reduced to $NADPH$. Dark reactions occur all the time and not just the dark. $NADP{H}^{+}$ and ATP produced in light reactions lead to the reductive synthesis of carbohydrate from $C{O}_2$ and $H_{2}O$. The site of photosynthesis is the chloroplast, which is under the surface of the leaf. The light reactions occur on the thylakoid membrane and the dark reactions occur within the stroma.