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

Options

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

Answer

**Step-by-Step Solution:**

1. **Understanding Fertilization**: Fertilization is the process where a male gamete (sperm) and a female gamete (egg) combine to form a new structure.

2. **Identifying the Options**: We have four options to consider:
- A) Sperm
- B) Embryo
- C) Fetus
- D) Zygote

3. **Analyzing Each Option**:
- **Sperm**: This is the male gamete and does not form after fertilization; it is involved in the fertilization process.
- **Embryo**: An embryo is formed after the zygote undergoes several divisions. It is multicellular, not single-celled.
- **Fetus**: A fetus is a later stage of development that occurs after the embryonic stage. It is also multicellular.
- **Zygote**: A zygote is the initial single-celled structure that forms immediately after the fertilization of the male and female gametes.

4. **Conclusion**: Among the options provided, the zygote is the only single-celled structure formed immediately after fertilization.

5. **Final Answer**: The correct answer is D) Zygote.

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