What is the number of light quanta required for the evolution of one `O_2` ?

Options

A. 8
B. 16
C. 24
D. 30

Answer

To determine the number of light quanta required for the evolution of one molecule of oxygen (O₂) during photosynthesis, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Photosynthesis**:
- Photosynthesis occurs in two main stages: the light-dependent reactions and the light-independent reactions (Calvin cycle). The light-dependent reactions are where oxygen is evolved.

2. **Role of Light Quanta**:
- Light quanta refer to the packets of energy (photons) absorbed by chlorophyll during the light-dependent reactions of photosynthesis.

3. **Photosystems Involved**:
- There are two photosystems involved in the light-dependent reactions: Photosystem I (PSI) and Photosystem II (PSII). These systems work together to convert light energy into chemical energy and produce oxygen.

4. **Oxygen Evolution**:
- The evolution of oxygen (O₂) occurs specifically during the splitting of water molecules (photolysis) in the light-dependent reactions. This process requires energy from light.

5. **Calculating Light Quanta**:
- It is established that to evolve one molecule of O₂, a total of 8 light quanta (photons) are required. This is because:
- 4 photons are needed for the splitting of 2 water molecules (which produces 1 O₂ molecule).
- Each water molecule requires 2 photons for the process.

6. **Final Answer**:
- Therefore, the number of light quanta required for the evolution of one molecule of O₂ is **8**.