Question

Synthesis of each molecule of glucose in photosynthesis involves:
a) 10 molecules of ATP
b) 8 molecules of ATP
c) 6 molecules of ATP
d) 18 molecules of ATP

Answer 1

Hint: The formation of glucose occurs in the chlorophyll of chloroplast by the Calvin cycle this cycle rotates 6 times to produce one molecule of glucose. And in each cycle, it required 3ATP and 2 NADPH molecules.

Complete answer:
The formation of glucose occurs in chlorophyll by the Calvin cycle, there are 3 steps in this cycle:
1-Carbon fixation
2-Reduction
3-Regeneration

- In the carbon fixation step, $CO_2$ reacts with RuBISCO (an enzyme) and forms 2 molecules of 3-PGA (3-phosphoglycerate), in this step 2 molecules of ATP are used.
- In the next step reduction, 2 molecules of NADPH are used and form Glyceraldehyde 3-phosphate which ultimately forms glucose.
- In the next step i.e. regeneration, the enzyme which catalyzes the reaction is regenerated and this step uses 1 ATP molecule.
- As we know that for the formation of one molecule of glucose this cycle repeats 6 times and the required amount of ATP is 18 (i.e, 6×3).

> The chemical reaction that takes place during photosynthesis is given below:
 \[6C{O_{2\;\;}} + \;6{H_2}O\;\; \to {\text{ }}{C_6}{H_{12}}{O_6}{\text{ }} + {\text{ }}6{O_2} + \;18ATP{\text{ }} + {\text{ }}12NADPH\]

Hence, the correct option is (d) 18 molecules of ATP.

Note: Photosynthesis involves 2 parts, light reaction, and dark reaction. During light reaction, 18 molecules of ATP formation take place which will be used during the dark reaction to prepare glucose molecules.