Phototrophs and chemotrophs are defined based on their

Options

A. Energy source
B. Requirement of organic and inorganic substances
C. Metabolism
D. Structure.

Answer

To answer the question "Phototrophs and chemotrophs are defined based on their...", we need to understand the definitions and characteristics of both groups of organisms.

### Step-by-Step Solution:

1. **Definition of Phototrophs**:
- Phototrophs are organisms that obtain their energy from sunlight. This energy is used to carry out cellular functions and metabolic processes.

2. **Definition of Chemotrophs**:
- Chemotrophs, on the other hand, are organisms that derive their energy from the oxidation of chemical compounds. This means they rely on chemical reactions involving inorganic or organic substances to obtain energy.

3. **Comparison of Energy Sources**:
- The primary distinction between phototrophs and chemotrophs lies in their energy sources:
- **Phototrophs**: Use sunlight as their energy source.
- **Chemotrophs**: Use energy obtained from the oxidation of chemical compounds.

4. **Conclusion**:
- Therefore, phototrophs and chemotrophs are defined based on their energy source. This is the key characteristic that differentiates them.

### Final Answer:
Phototrophs and chemotrophs are defined based on their energy source.

---