Reproduction: How Life Continues · Lesson 5 of 12
Fertilisation and Seed Formation
“A tiny pollen grain starts a journey that can end with an entire fruit.”
• Trace events from pollen arrival to zygote formation. • Explain the function of the pollen tube. • Distinguish pollination from fertilisation. • Describe how ovules become seeds and the ovary becomes a fruit. • Connect seed dispersal and germination with the next generation.
Fertilisation
Pollination delivers pollen to the correct surface, but delivery alone does not form a seed. The male gamete is still separated from the egg inside an ovule. A growing pollen tube creates the route that brings them together.
When a compatible pollen grain reaches the stigma, it germinates. A pollen tube grows from it, passes down through the style and enters the ovary. The male gamete travels through this tube towards an ovule containing the egg cell.
Fertilisation is the fusion of a male gamete and a female gamete.
A zygote is the fertilised egg formed when the male gamete fuses with the egg cell.
The fusion begins the development of a new individual. The zygote divides and develops into an embryo. At the same time, surrounding flower structures change. The ovule containing the developing embryo becomes a seed, and the ovary surrounding the ovules enlarges into a fruit.
Problem
Trace what happens to an ovule after successful fertilisation.
- 1.The pollen tube reaches the ovule.
- 2.The male gamete fuses with the egg cell.
- 3.A zygote forms and develops into an embryo.
- 4.The ovule develops into a seed containing the young plant.
- 5.The surrounding ovary develops into a fruit.
| Stage | Location | What happens |
|---|---|---|
| Pollination | Stigma | Pollen is transferred from anther to stigma. |
| Pollen germination | Stigma | A pollen tube begins growing. |
| Tube growth | Style towards ovary | The male gamete is carried towards an ovule. |
| Fertilisation | Ovule | Male gamete fuses with egg cell. |
| Zygote development | Within ovule | The embryo begins forming. |
| Fruit and seed formation | Ovary and ovules | Ovary becomes fruit; ovules become seeds. |
Pollination is pollen transfer. Fertilisation is the later fusion of gametes. Pollination makes fertilisation possible but the two terms describe different events.
Seeds must reach places where a new plant can grow. Wind can carry lightweight seeds, water can move floating seeds, and animals can transport seeds on their bodies or after eating fruits. Dispersal reduces crowding near the parent and spreads the next generation to new places.
A dispersed seed remains inactive until conditions become favourable. Water activates processes within the seed, air supplies oxygen and a suitable temperature supports growth. The embryo resumes development, a root emerges and the shoot grows towards light. This is germination.
Problem
What can the arrangement of seeds in a tomato reveal about the earlier flower?
- 1.The fruit developed from the ovary.
- 2.Each seed developed from an ovule.
- 3.The positions of the seeds reflect how ovules were attached within the ovary.
- 4.Longitudinal and transverse fruit sections can therefore be compared with corresponding ovary sections.
Sexual reproduction produces seeds with new genetic combinations. Even plants growing from the same fruit need not be identical. This variation can help some individuals survive changes in climate, disease or other environmental conditions.
Quiz
Which description best matches Fertilisation?
Which description best matches Zygote?
Which term matches this description: Fertilisation is the fusion of a male gamete and a female gamete.
Which term matches this description: A zygote is the fertilised egg formed when the male gamete fuses with the egg cell.
Which statement is a key takeaway from this lesson?
Practice Problems
- Arrange pollination, pollen-tube growth, fertilisation, zygote formation and seed formation in order.
- What is the function of the pollen tube?
- Where does fertilisation occur in a flowering plant?
- Complete the relationships: ovule becomes ___; ovary becomes ___.
- Distinguish a zygote from an embryo.
- Name three agents of seed dispersal.
- Why are water, air and a suitable temperature required for germination?
Key Takeaways
• A compatible pollen grain germinates on the stigma. • Its pollen tube grows through the style to an ovule. • Fusion of gametes forms a zygote. • The zygote develops into an embryo, the ovule becomes a seed and the ovary becomes a fruit. • Dispersal and germination establish the next generation.