Question

Choose the event that does not occur in photosynthesis.

• A. Absorption of light energy by chlorophyll
• B. Reduction of carbon dioxide to carbohydrates
• C. Oxidation of carbon to carbon dioxide
• D. Conversion of light energy to chemical energy

Answer 1

The correct option is C Oxidation of carbon to carbon dioxide

Hint: Photosynthesis is the process by which plants use sunlight, water, and carbon dioxide to create oxygen and energy as sugar.

Part 1 - Definition - Photosynthesis

• Photosynthesis is the process of preparing food in the presence of sunlight and chlorophyll.
• In this process, the plant uses water from the soil, carbon dioxide from the air, and energy from sunlight to prepare glucose.

$Carbon$ $dioxide$ + $Water$ + $light$ $energy$ → $Glucose$ + $Oxygen$

Part 2 - Oxidation of water to oxygen

• During the initial phase of photosynthesis, light energy is harvested to produce $ATP$ and $NADPH$ where water is oxidized to provide electrons and protons.
  
• The reaction proceeds as follows:

$H_{2}O$ → $2H^{+}$ + $2e^{-}$ + $1/2O_2$

Part 3 - Reduction of $C{O}_2$ to carbohydrate

• After the formation of $ATP$ and $NADPH$, carbon dioxide is reduced to carbohydrates (glucose)
  
• The reduction of carbon dioxide to carbohydrates doesn't directly depend on the presence of sunlight but on the supply of $ATP$ and $NADPH$ that were formed during the initial phase.
  

Part 4- Conclusion

• From the above discussion, we can conclude that within the plant cell, the water is oxidized, meaning it loses electrons, while the carbon dioxide is reduced, meaning it gains electrons. This transforms the water into oxygen and the carbon dioxide into glucose.
  

Final step: Oxidation of carbon to carbon dioxide doesn't occur during photosynthesis.