Question

Assertion: Six molecules of ${ CO }_{ 2 }$, twelve molecules if ${ NADPH }^{ + }{ H }^{ + }$ and eighteen ATP are required to form one hexose molecule
Reason: The light reaction produces ATP and ${ NADPH }^{ + }{ H }^{ + }$
(a)Both assertion and reason are correct and the reason is the correct explanation for assertion
(b)Both assertion and reason are correct but the reason is not the correct explanation for assertion
(c)Assertion is correct but the reason is incorrect
(d)Both assertion and reason are correct

Answer 1

Hint: Photosynthesis involves light and dark reaction that occurs with and without the presence of sunlight respectively. The products obtained in the light reaction are used in the dark reaction to give rise to the 6 carbon molecules named glucose.

Complete answer:
Here both Assertion and Reason are correct but the reason is not the correct explanation for the assertion.
In Photosynthesis, we can see that ATP and NADPH are used in the synthesis of carbohydrates. The ATP and NADPH are produced during the Light reaction. And the production of carbohydrates from these is part of the dark reaction. The Net reaction of the ${ C }_{ 3 }$ cycle of dark reaction is given below
$6RUBP+6{ CO }_{ 2 }+18ATP+12NADPH\xrightarrow [ ]{ } 6RUBP+{ C }_{ 6 }{ H }_{ 12 }{ O }_{ 6 }+18ADP+12NADP++18Pi$
From this, we can see that 6 molecules of carbon, 18 ATP, and 12 molecules of NADPH are required to give rise to one hexose molecule i.e. glucose.

So, the correct answer is “Both assertion and reason are correct and the reason is the correct explanation for assertion”.

Note:The light reaction of photosynthesis occurs in presence of light and involves steps like absorption of light, splitting of water, the release of oxygen, and finally formation of ATP and NADPH. In cyclic photophosphorylation, only PS-I is involved and forms ATP. ${ NADPH }^{ + }{ H }^{ + }$ is formed in the non-cyclic photophosphorylation where both PS-I and PS-II are involved.
In the dark reaction of photosynthesis, ${ C }_{ 3 }$, and ${ C }_{ 4 }$ cycles are involved. ${ C }_{ 3 }$ cycle occurs in steps like carbon fixation, reduction, and regeneration. The ATP and NADPH produced during light reaction work in this cycle and the end product shows the 6 carbon compounds named glucose.