All functions of the body are carried out by a single cell in

Options

A. Multicellular organism
B. Hen
C. Virus
D. Unicellular organism

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks which type of organism carries out all functions of the body through a single cell.

2. **Identifying Organism Types**:
- **Unicellular Organisms**: These organisms consist of only one cell. Examples include bacteria and amoeba.
- **Multicellular Organisms**: These organisms are made up of many cells. Examples include humans, plants, and animals.
- **Viruses**: Viruses are not classified as living organisms because they cannot carry out life processes on their own and require a host cell to replicate.

3. **Analyzing Functions of Cells**:
- In unicellular organisms, all life functions (such as metabolism, reproduction, and response to stimuli) are performed by that single cell.
- In multicellular organisms, different cells perform different functions, and they work together to maintain the life of the organism.

4. **Conclusion**: Since the question specifies that all functions of the body are carried out by a single cell, the correct answer is **unicellular organisms**.

### Final Answer:
All functions of the body are carried out by a single cell in **unicellular organisms**.

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