One of the following processes is not a step involved in the water-cycle operation in nature

Options

A. evaporation
B. transpiration
C. precipitation
D. photosynthesis

Explanation

To determine which process is not involved in the water cycle, we can analyze each option given:

1. **Evaporation**: This is a key process in the water cycle where water is converted from liquid to vapor due to heat from the sun. This process is essential for the movement of water from the earth's surface into the atmosphere.

2. **Transpiration**: This process involves the release of water vapor from plants into the atmosphere. It is another important component of the water cycle, as it contributes to the moisture in the air.

3. **Precipitation**: This is the process where water vapor condenses and falls back to the earth in various forms such as rain, snow, or hail. It is a critical step in the water cycle, returning water to the surface.

4. **Photosynthesis**: This is the process by which plants use sunlight to convert carbon dioxide and water into glucose and oxygen. While it involves water, it is primarily part of the carbon cycle and not directly a part of the water cycle.

Based on this analysis, the process that is not involved in the water cycle is **photosynthesis**.

### Final Answer:
**Photosynthesis (Option D)** is not a step involved in the water cycle.