Which is the correct order of stages in human reproduction?

(a) Fertilization → Zygote → Embryo → Foetus

(b) Embryo → Zygote → Fertilization → Foetus

(c) Zygote → Fertilization → Embryo → Foetus

(d) Fertilization → Embryo → Zygote → Foetus

The correct answer is (a) Fertilization → Zygote → Embryo → Foetus

Human reproduction follows a specific sequence of events:

1. Fertilization: The male gamete (sperm) fuses with the female gamete (egg) inside the fallopian tube to form a single cell.
2. Zygote: This single cell formed after fertilization is called the zygote. It is the first stage of a new organism.
3. Embryo: The zygote undergoes repeated cell divisions (mitosis) and forms a multicellular structure called the embryo.
4. Foetus: As the embryo develops further, it takes on a recognizable human shape. At this stage, it is called a foetus.

Why the Other Options Are Wrong:

• (b) Embryo → Zygote → Fertilization → Foetus: Wrong order — fertilization must occur first to form the zygote.
• (c) Zygote → Fertilization → Embryo → Foetus: Wrong — fertilization comes before zygote formation.
• (d) Fertilization → Embryo → Zygote → Foetus: Wrong — zygote is formed immediately after fertilization, before the embryo stage.

Thus, the correct and logical order is Fertilization → Zygote → Embryo → Foetus.