Sexual and asexual reproduction: pollen and egg cells in flowering plants.

The idea

Flowering plants reproduce sexually using specialised gametes: pollen grains (male) and egg cells, also called ova (female). Pollen is made in the anther of the stamen; each pollen grain contains a male nucleus and is carried by wind or insects to the stigma. The egg cell sits inside the ovule in the ovary. When a pollen tube grows down the style, the male nucleus fuses with the egg nucleus in fertilisation, forming a zygote that develops into an embryo inside a seed. The ovule becomes the seed and the ovary becomes the fruit. Both gametes are haploid, so fusion restores the diploid chromosome number.

What earns the marks

• Pollen grains are the male gametes and are produced in the anther of the stamen.
• Egg cells (ova) are the female gametes and are found inside the ovule within the ovary.
• Pollen is transferred to the stigma by wind or insects, then a pollen tube grows down the style to the ovule.
• Fertilisation is the fusion of the male nucleus from the pollen grain with the female nucleus of the egg cell.
• After fertilisation the ovule becomes the seed and the ovary develops into the fruit.

Common mistakes and how to put them right

• Saying pollen is the male sex cell and stopping there.

  Put it right by naming the male nucleus inside the pollen grain as the gamete that fuses.

• Confusing the ovary with the ovule.

  Put it right by stating the ovule contains the egg cell and becomes the seed, while the ovary becomes the fruit.

• Thinking pollen travels down the pollen tube.

  Put it right by stating the pollen tube grows down the style carrying the male nucleus to the egg cell.

Exam tips

• Label a flower diagram with anther, stigma, style, ovary and ovule, then state the job of each part.
• Use the phrase 'fusion of the male nucleus and egg nucleus' rather than vague wording such as 'they join'.
• Link each structure to its fate after fertilisation: ovule to seed, ovary to fruit.