Question

How many quanta of lights are required to evolve one oxygen molecule in photosynthesis?
A. Three
B. Eight
C. Four
D. Two

Answer 1

Hint: During photosynthesis, the light-dependent reactions take place through photosystem 1 and photosystem 2. The plant receives the light from the sun in the form of photons. Half the photons are required by photosystem 1 and the other half are required by photosystem 2. The number of photons is dependent on the molecules of oxygen being utilised by the plant.

Complete answer:
- Eight photons of light are required to evolve one molecule of oxygen during photosynthesis.
- As we already know, photosynthesis occurs in two stages- light-dependent reactions and light-independent reactions.
- Light-dependent reactions require light as a source of energy. The light from the sun provides photons and initiates the process of photosynthesis and produces chemical energy in the form of ATP and NADPH.
- Photosystem 1 (PS1) and photosystem 2 (PS2) are present in the thylakoids of the chloroplasts.
- Carbon dioxide from the atmosphere is converted into carbohydrates with the help of chemical energy.
- The light energy also enters water and gains electrons from the PS2, which then move to the PS1 and reduce as energy. The electrons gain energy and produce NADPH.
- Eventually, two types of reactions can occur – cyclic photophosphorylation and non-cyclic photophosphorylation. Both result in the production and maintenance of the chemical energy.

Hence, the correct answer is option (B).

Note: In the light reaction, the energy from the sun in the form of photons is converted into chemical energy that is stored in the form of ATP and NADPH. Four photons enter the photosystem 1 and four photons are utilised by the photosystem 2. Oxygen is the waste product that is generated in the light-dependent reaction.