Best defined function of manganese in green plants is

Options

A. Nitrogen fixation
B. Water absorption
C. Photolysis of water
D. Calvin cycle

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the best-defined function of manganese in green plants. We need to evaluate the given options: nitrogen fixation, water absorption, photolysis of water, and the Calvin cycle.

2. **Evaluating Nitrogen Fixation**: Nitrogen fixation is primarily carried out by certain bacteria in the soil and atmosphere, not directly by manganese in plants. Thus, this option is not correct.

3. **Evaluating Water Absorption**: Water absorption in plants is mainly performed by the roots. While manganese may play a role in overall plant health, it is not specifically known for facilitating water absorption. Therefore, this option is also not correct.

4. **Evaluating Photolysis of Water**: Photolysis of water refers to the process in which water molecules are split into oxygen and hydrogen ions using light energy. Manganese ions are crucial in this process as they help in the liberation of oxygen from water during photosynthesis. This is a key function of manganese in green plants.

5. **Evaluating the Calvin Cycle**: The Calvin cycle is a series of biochemical reactions that take place in the chloroplasts of plants, which do not directly involve manganese in its primary function. It is more about carbon fixation rather than the role of manganese.

6. **Conclusion**: Based on the evaluations, the best-defined function of manganese in green plants is **photolysis of water**. This process is essential for photosynthesis and involves the release of oxygen, which is facilitated by manganese.