Question

How much energy in terms of ATP equivalents is consumed in the photosynthetic production of a mole of hexose?
A. 36 ATP eq
B. 38 ATP eq
C. 40 ATP eq
D. 54 ATP eq

Answer 1

Hexose is a monosaccharide sugar with six carbons. It has the same chemical formula as glucose. It exists in two forms open-chain and cyclic. This sugar is the energy source for plants which do the photosynthesis and make their food.

Complete answer:
Photosynthesis is the process of making plant food in the presence of sunlight. This process occurs in the chlorophyll in the plastids. The photosynthesis process is done by absorbing the sunlight and converting it into chemical energy. They need sunlight to make their food. Conversion of sunlight to chemical energy needs electrons, ATP, NADPH etc. they run through a cascade to produce $C{O_2}$, water and energy.
In ${C_3}$ plants, 1 carbon atom needs 3 molecules of ATP
So 6 carbon molecules will need = $6 \times 3$
= 18 ATP
Other than ATP, we have energy molecules like $NADP{H_2}$,
For 1 carbon we need 2 molecules of $NADP{H_2}$
So for 6 carbon, we need = $6 \times 2$
= 12 $NADP{H_2}$ molecules
We know 1 $NADP{H_2}$ molecule is equivalent to 3 molecules of ATP
So 12 $NADP{H_2}$ = $12 \times 3$
= 36 ATP
Now total ATP equivalent molecules = $18 + 36$
= 54 ATP equivalent

So the answer is option D: 54 ATP eq.

Note: Dark reaction was given by Calvin. This reaction is also called the ${C_3}$ cycle or the reductive pentose phosphate process. The plants carrying out the Calvin cycle are called ${C_3}$ plants. The Calvin cycle occurs in three steps- fixation, reduction and regeneration. The dark reaction does not depend on the light reaction but depends on the products of the light reaction.