Photosynthetic autotrophs get their energy requirement from

Options

A. Heat
B. Light
C. Inorganic chemicals
D. Organic chemicals.

Answer

### Step-by-Step Solution:

1. **Understanding Photosynthetic Autotrophs**:
- Photosynthetic autotrophs are organisms that can produce their own food using light energy. The term "photo" refers to light, and "synthesis" refers to the process of making or producing.

2. **Role of Light**:
- The primary source of energy for photosynthetic autotrophs is light. They utilize light energy to convert inorganic substances (like carbon dioxide and water) into organic compounds (like glucose).

3. **Photosynthetic Pigments**:
- These organisms contain specialized pigments (such as chlorophyll) that absorb light energy. This is a key characteristic that distinguishes them from heterotrophs, which cannot produce their own food.

4. **Energy Conversion Process**:
- When light is absorbed by these pigments, it triggers a series of reactions that convert light energy into chemical energy. This chemical energy is stored in the form of glucose, which can later be converted into ATP (adenosine triphosphate) for cellular energy.

5. **Conclusion**:
- Therefore, the energy requirement for photosynthetic autotrophs comes primarily from light. The other options (heat, inorganic chemicals, organic chemicals) do not serve as a direct energy source for these organisms.

### Final Answer:
Photosynthetic autotrophs get their energy requirement from **light**.