Which of these is a single-celled structure formed after fertilization?

Options

A. Embryo
B. Foetus
C. Sperm
D. Zygote

Answer

To answer the question, "Which of these is a single-celled structure formed after fertilization?" we need to follow these steps:

### Step-by-Step Solution:

1. **Understand Sexual Reproduction**:
- Sexual reproduction involves the production of gametes (sperm and egg cells).

2. **Identify Gametes**:
- There are two types of gametes: male gametes (sperm) and female gametes (ova or egg cells).

3. **Fertilization Process**:
- Fertilization occurs when a sperm cell fuses with an egg cell. This fusion is a crucial step in sexual reproduction.

4. **Formation of Zygote**:
- The result of the fertilization process is a zygote. The zygote is a single-celled structure, meaning it is unicellular.

5. **Differentiate Between Structures**:
- After the zygote stage, the next stages of development are the embryo (multicellular) and then the fetus (also multicellular).

6. **Identify the Correct Answer**:
- Among the options provided, the zygote is the only single-celled structure formed after fertilization.

### Conclusion:
The correct answer is **Zygote**, as it is the unicellular structure formed after the fertilization of the sperm and egg.

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