In simple organisms, the two fusing germ-cells may look identical, but in complex organisms one gamete is lar…

Question

In simple organisms, the two fusing germ-cells may look identical, but in complex organisms one gamete is large and non-motile while the other is small and motile. Give a biological explanation for why gametes in complex organisms are differentiated in this way, and state what each design feature achieves.

Accepted Answer

## Model Answer In complex organisms, gametes are differentiated because each serves a distinct function during sexual reproduction. - **Large, non-motile gamete (egg/ovum):** Its large size provides stored nutrients (food reserves) to nourish the developing embryo after fertilisation. - **Small, motile gamete (sperm):** Its small size and motility enable it to travel and reach the egg for fertilisation. This division of labour ensures both successful fertilisation (by the mobile sperm) and adequate nourishment for the new organism's development (by the nutrient-rich egg). *Source: Chapter 7, Sexual Reproduction section* --- ## Explanation The examiner wants two clear design features linked to two functions: (1) large + non-motile → stores food/nutrients for embryo; (2) small + motile → can move to reach the egg. Many students state the features but forget to explain **what each achieves** — that costs marks. Keep each point in a paired "feature → function" format.

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