Most of the plants are seasonal due to
(a) Photoperiodism
(b) Phototropism
(c) Photosynthesis
(d) Photolysis

Options

A. Photoperiodism
B. Phototropism
C. Photosynthesis
D. Photolysis

Answer

To solve the question regarding why most plants are seasonal, we will analyze each option provided:

1. **Understanding the Question**: The question asks why most plants exhibit seasonal behavior. This implies that we need to identify the factor that influences plant growth and development in relation to seasons.

2. **Evaluating the Options**:
- **(a) Photoperiodism**: This refers to the physiological reaction of organisms to the length of day or night. In plants, it determines flowering and other growth patterns based on the duration of light exposure. Plants can be classified as short-day, long-day, or day-neutral based on their photoperiodic responses.
- **(b) Phototropism**: This is the growth of a plant in response to light direction. While it affects how plants grow towards light, it does not explain seasonal changes.
- **(c) Photosynthesis**: This is the process by which plants convert light energy into chemical energy. While essential for plant growth, it does not directly relate to the seasonal behavior of plants.
- **(d) Photolysis**: This is the process of breaking down molecules using light, often referring to the splitting of water molecules in photosynthesis. It is not related to seasonal changes in plants.

3. **Conclusion**: Based on the analysis, the correct answer is **(a) Photoperiodism**. This is because photoperiodism directly influences the seasonal growth patterns of plants by determining when they flower and grow based on the length of daylight.

### Final Answer:
Most of the plants are seasonal due to (a) Photoperiodism.