Plant life cycles and reproduction

A flowering plant’s life goes round in a cycle. A seed germinates and grows into a plant. The plant flowers, its flowers are pollinated, and fertilisation makes new seeds. The seeds are spread away from the parent plant, and the cycle starts again.

Key facts

  • The life cycle: seed → germination → seedling → adult plant → flowering → pollination → fertilisation → seeds → seed dispersal.
  • A seed needs water, warmth and oxygen to germinate (start to grow). Most seeds don’t need light: they use food stored in the seed until their first leaves can make food.
  • Parts of a flower: petals attract insects; sepals protect the bud; the stamen (anther and filament) makes pollen; the carpel (stigma, style and ovary) holds the ovules.
  • Pollination: pollen moves from an anther to a stigma, carried by insects or the wind. Fertilisation: the nucleus of a pollen grain joins the nucleus of an ovule.
  • After fertilisation the ovules become seeds and the ovary becomes the fruit.
  • Seeds are dispersed (spread) by the wind, by animals, by water or by bursting out of pods, so the new plants don’t compete with the parent for light, water, nutrients and space.
  • Insect-pollinated flowers have bright petals, scent and nectar. Wind-pollinated flowers are small and dull, with anthers and stigmas hanging outside and lots of light pollen.

Worked examples

Example 1

Put these stages in order: pollination, germination, seed dispersal, fertilisation, flowering.

  1. A seed must first germinate: it takes in water and starts to grow.
  2. The seedling grows into an adult plant, which makes flowers.
  3. Insects or the wind carry pollen to another flower: pollination.
  4. A pollen nucleus joins an ovule nucleus: fertilisation. The ovules grow into seeds.
  5. The seeds are spread away from the plant, ready to germinate: the cycle begins again.

Answer: germination → flowering → pollination → fertilisation → seed dispersal

Example 2

Label the parts of this flower. Which parts make up the stamen and which make up the carpel?

  1. The petals attract insects; the green sepals protected the flower when it was a bud.
  2. Each stamen is an anther, which makes pollen, on a thin stalk called the filament.
  3. In the middle is the carpel: the sticky stigma catches pollen, the style holds it up, and the ovary at the bottom holds the ovules.

Answer: stamen = anther + filament (makes pollen); carpel = stigma + style + ovary (holds the ovules)

Example 3

Grass flowers have no bright petals and no scent, and their feathery stigmas and anthers hang outside the flower. How are they pollinated?

  1. There are no bright petals, scent or nectar, so nothing attracts insects.
  2. The anthers hang out in the open air, so the wind can blow their light pollen away.
  3. The feathery stigmas catch pollen from the air. So grass is wind-pollinated.

Answer: by the wind

Example 4

Kai plants 40 seeds and 34 of them germinate. What percentage germinated?

  1. Write the fraction that germinated. 34/40
  2. Divide, then multiply by 100. 34 ÷ 40 × 100 = 85%

Answer: 85%