Which is not true regarding ecosystem?

Options

A. Self sufficient unit
B. Cyclic exchange of materials between living beings and environment
C. Only requirement is input of energy
D. Characterized by a major vegetation type

Explanation

### Step-by-Step Solution:

1. **Understanding Ecosystem**:
- An ecosystem is defined as a functional unit of ecology that encompasses the interactions between living organisms (biotic components) and their physical environment (abiotic components).

2. **Evaluating Options**:
- The question asks which statement is **not true** regarding ecosystems. We need to analyze each option provided.

3. **Option Analysis**:
- **Option 1**: "It is a self-sufficient unit."
- This is true because ecosystems can sustain themselves through the interactions of their components.
- **Option 2**: "It is a cyclic exchange of materials between the living beings and the environment."
- This is also true as ecosystems involve cycles like the water cycle, carbon cycle, etc.
- **Option 3**: "Only requirement is the input of energy."
- This statement is true because ecosystems require energy input (usually from the sun) to function.
- **Option 4**: "Characterized by a major vegetation type."
- This statement is **not true** regarding ecosystems. This description fits more accurately with biomes, which are larger areas defined by their dominant vegetation types. Ecosystems can exist within various biomes and are not solely characterized by a major vegetation type.

4. **Conclusion**:
- Based on the analysis, the statement that is not true regarding ecosystems is **Option 4**: "Characterized by a major vegetation type."

### Final Answer:
The correct answer is **Option 4**: "Characterized by a major vegetation type."

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