After a pollen grain lands on the stigma of a flower, a series of events leads to fertilisation and the formation of seeds and fruit. Fig. 2.3 shows a half-...

This question tests the events from pollination to fertilisation, what the flower parts become afterwards, and the value of seed dispersal.

(a) The events after a pollen grain lands on the stigma [4]: the pollen grain grows a pollen tube [1]; the tube grows down the style [1]; it passes through the ovary to an ovule, entering through the micropyle [1]; the male gamete nucleus fuses with the female gamete nucleus inside the ovule [1]. That final fusion is fertilisation.

(b) Fertilisation takes place in the ovule (inside the ovary) [1].

(c) After fertilisation, each ovule develops into a seed [1].

(d) The ovary develops into a fruit [1]. A common mix-up is to swap these: the ovule becomes the seed, the whole ovary becomes the fruit that contains the seeds.

(e) Sexual reproduction gives variation because [3]: gametes come from two parents (or two different plants) and combine [1]; these gametes are genetically different / carry different alleles [1]; so the offspring receive new combinations of alleles not identical to either parent [1].

(f) Any two methods of seed dispersal [2]: by wind; by animals (eaten and passed out, or carried on fur); by water; by explosive or self dispersal.

(g) One advantage of dispersal [2]: it reduces competition between the offspring and parent (and between offspring) for light, water and minerals [1]; so more seedlings survive, or new areas are colonised [1]. Seeds landing right under the parent would compete with an already-established plant.