Which statement is correct ?

Options

A. All bacteria are autotrophic
B. All bacteria are heterotrophic
C. All bacteria are photosynthetic
D. Mostly bacteria are heterotrophic but some are autotrophic.

Answer

To determine which statement about bacteria is correct, we need to analyze the options provided and understand the modes of nutrition in bacteria. Here’s a step-by-step breakdown:

### Step 1: Understand the Modes of Nutrition in Bacteria
Bacteria can be classified based on their modes of nutrition into two main categories: autotrophic and heterotrophic.

### Step 2: Define Autotrophic Bacteria
Autotrophic bacteria can synthesize their own food. This can occur through:
- **Photo-autotrophic**: Using light energy (e.g., cyanobacteria).
- **Chemo-autotrophic**: Using chemical energy from inorganic substances.

### Step 3: Define Heterotrophic Bacteria
Heterotrophic bacteria cannot synthesize their own food and must obtain it from other sources. They can be:
- **Parasitic**: Deriving nourishment from a host.
- **Symbiotic**: Living in a mutually beneficial relationship (e.g., nitrogen-fixing bacteria like Rhizobium).
- **Saprophytic**: Feeding on dead organic matter, playing a crucial role in decomposition.

### Step 4: Analyze the Statements
1. **All bacteria are autotrophic**: This is incorrect because not all bacteria can synthesize their own food.
2. **All bacteria are heterotrophic**: This is also incorrect as some bacteria are autotrophic.
3. **Photosynthetic**: This is misleading because while some bacteria are photosynthetic, not all are.
4. **Some bacteria are heterotrophic but others are autotrophic**: This statement is correct as it acknowledges the diversity in nutritional modes among bacteria.

### Conclusion
The correct statement is: **Some bacteria are heterotrophic but others are autotrophic.**