Plant Reproduction: Pollination, Seeds & Dispersal — Complete PSLE Guide

Reproduction is one of the characteristics of living things, and plants have evolved fascinating ways to reproduce. In Singapore Primary Science, plant reproduction is a major P5 and PSLE topic. You need to understand the parts of a flower, how pollination works, how seeds form after fertilisation, and how seeds are dispersed so new plants can grow in new locations.

Parts of a Flower and Their Functions

Flowers are the reproductive organs of flowering plants. Each part has a specific function in reproduction.

• Petals — attract insects and animals for pollination; often brightly coloured and scented
• Sepals — protect the flower bud before it opens
• Stamen (male part) — consists of the anther (produces pollen grains) and filament (supports the anther)
• Pistil/Carpel (female part) — consists of the stigma (receives pollen), style (connects stigma to ovary), and ovary (contains ovules which become seeds after fertilisation)
• Nectary — produces nectar to attract pollinators such as bees and butterflies

Pollination

Pollination is the transfer of pollen grains from the anther of one flower to the stigma of another flower of the same species. Pollination must happen before fertilisation can occur.

There are two main types of pollination:

• Self-pollination — pollen is transferred from the anther to the stigma of the same flower or another flower on the same plant
• Cross-pollination — pollen is transferred from the anther of one plant to the stigma of a different plant of the same species (generally produces stronger offspring)

Agents of Pollination

Pollen cannot move by itself — it needs an agent to carry it. The two main agents in Singapore Primary Science are insects and wind.

Fertilisation and Seed Formation

After pollination, the pollen grain germinates (sprouts) on the stigma and grows a pollen tube down through the style into the ovary. The male sex cell travels down this tube to reach and fuse with an ovule. This fusion is called fertilisation.

After fertilisation, the ovule develops into a seed, and the ovary develops into a fruit. The fruit protects the seed and often helps with seed dispersal.

Seed Dispersal

Seeds need to be dispersed (scattered) away from the parent plant so they do not compete for light, water, and nutrients. There are four main methods of seed dispersal tested in Singapore Primary Science.

1. Wind Dispersal

Seeds adapted for wind dispersal are usually very light with special structures to catch air currents.

• Wings — seeds like Angsana (winged seeds that spin as they fall, staying airborne longer)
• Parachute-like structures — dandelion seeds have feathery tufts (pappus) that act like parachutes
• Very small and light — some seeds are so tiny they float like dust

2. Water Dispersal

Seeds dispersed by water float and are waterproof. They have a spongy or fibrous outer layer that traps air, allowing them to float long distances. The coconut is the most famous example — its hard outer shell is waterproof and it floats for months across oceans before washing ashore.

3. Animal Dispersal

Animals disperse seeds in two ways: by eating fleshy fruits and excreting the seeds elsewhere, or by carrying seeds on their fur or feathers. Seeds adapted for animal dispersal include those with hooks or spines that stick to animal fur (e.g., burdock), and fleshy, sweet fruits that attract animals (e.g., mango, papaya).

4. Explosive/Self-Dispersal

Some plants have fruit pods that dry out and burst suddenly, flinging seeds outward. Examples include the sandbox tree and the touch-me-not plant (Mimosa). These pods build up tension as they dry, then release it explosively.

Model Exam Answers

Question: Explain how the structure of the Angsana seed makes it adapted for wind dispersal.

Model Answer: The Angsana seed has a flat, papery wing attached to it. When the seed falls from the tree, the wing causes it to spin and slow its descent, keeping it airborne for longer. This allows the wind to carry it further away from the parent plant.

Question: State the difference between pollination and fertilisation.

Model Answer: Pollination is the transfer of pollen grains from the anther of a flower to the stigma of another flower of the same species. Fertilisation is the fusion of the male sex cell from the pollen with the female sex cell (ovule) inside the ovary. Pollination must occur before fertilisation can take place.