16.3 Sexual Reproduction in Plants

2026 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Identify and draw the sepals, petals, stamens (anthers and filaments) and carpels (stigmas, styles, ovaries and ovules) of an insect-pollinated flower
  2. Identify and draw the anthers and stigmas of a wind-pollinated flower
  3. Relate the structure of the parts of flowers to their functions
  4. Compare the flower structure and pollen from insect-pollinated and wind-pollinated flowers
  5. Outline the process of pollination and distinguish between self-pollination and cross-pollination
  6. Discuss the potential effects of self-pollination and cross-pollination on a population
  7. Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation
  8. Understand that after fertilisation, ovules develop into seeds and the ovary develops into a fruit
  9. Investigate and describe the structure of a seed (embryo: radicle, plumule, cotyledons; and testa)
  10. Understand that seed and fruit dispersal by wind and by animals is a means of colonising new areas and reducing competition
  11. Relate the features of wind-dispersed and animal-dispersed fruits to their functions
  12. Investigate and state the environmental conditions that affect germination (suitable temperature, water, oxygen)
  13. Describe the process of germination, including the role of enzymes

Main Content

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Section 1: The Flower — The Reproductive Organ of a Plant

Flowers are the reproductive organs of plants. Their job is to bring together the male and female sex cells (called gametes) so that fertilisation can take place.

  • The male gametes of a plant are found inside pollen grains
  • The female gametes are found inside structures called ovules

Section 2: Parts of an Insect-Pollinated Flower

An insect-pollinated flower has several key parts. You need to be able to identify and draw all of them.

The Male Parts — The Stamen

The stamen is the male reproductive part of the flower. It is made up of two parts:

  • Anther — the part at the top of the stamen. It produces and releases pollen grains. Think of it as a tiny pollen factory.
  • Filament — the stalk that holds the anther up. It supports the anther and keeps it in position inside the flower so that it can brush against visiting insects.

The Female Parts — The Carpel

The carpel is the female reproductive part of the flower. It has three parts:

  • Stigma — the very top of the carpel. It has a sticky surface that catches and holds pollen grains when they land on it. Think of it like sticky tape waiting to trap pollen.
  • Style — the tube connecting the stigma to the ovary below. It supports the stigma and acts as a pathway for the pollen tube to grow down.
  • Ovary — the rounded structure at the base of the carpel. It contains the ovules (the female sex cells).
  • Ovule — found inside the ovary. Each ovule contains a female gamete (egg cell). After fertilisation, ovules develop into seeds.

The Non-Reproductive Parts

  • Petals — in insect-pollinated flowers, petals are large and brightly coloured to attract insects. They may also produce scent and nectar (a sweet sugary liquid) as rewards to encourage insects to visit.
  • Sepals — small, usually green, leaf-like structures found at the base of the flower. They protect the unopened flower bud before the flower opens. Think of them as a protective jacket.

Diagram Guide: Insect-Pollinated Flower (Cross-Section)

When drawing a flower cross-section, make sure to include and label:

         Petal
           |
   Anther (on top of Filament) → Stamen
           |
        Stigma
           |
         Style   → Carpel
           |
         Ovary (containing Ovules)
           |
         Sepal (at the base)

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