By the end of this lesson
- Sequence events from pollination to fertilisation.
- Explain pollen-tube function.
- State how ovule and ovary develop after fertilisation.
BIG QUESTION
How does a pollen grain on a stigma become a seed inside a fruit?
Pollen-tube growth connects pollination to fertilisation and subsequent development.
Compatible pollen germinates
A compatible pollen grain absorbs water and germinates on the stigmaThe sticky tip of the carpel in a flower that receives pollen.. A pollen tubeA tube that grows from a pollen grain down through the style to the ovule, carrying the male nucleus for fertilisation. grows down through the style toward an ovule.
The tube is a growth from the pollen grain; the whole pollen grain does not travel down the style.
The male nucleus reaches an ovule
A male gamete nucleus travels inside the pollen tube. The tube enters an ovule and the male nucleus fuses with the female gamete nucleus.
This nuclear fusion is fertilisation and forms a diploid zygote.
Flower tissues become dispersal structures
The zygote divides to form an embryo. The ovule develops into a seed, including a protective seed coat and food reserve.
The ovary develops into a fruit, which protects seeds and can assist their dispersal.
From flower to fruit
Separate the transport event from the developmental outcomes.
| Stage/structure | Change | Outcome |
|---|---|---|
| Pollen on stigma | Germinates. | Pollen tube begins. |
| Style | Pollen tube grows through tissue. | Male nucleus is delivered. |
| Ovule | Gamete nuclei fuse. | Diploid zygote forms. |
| Zygote | Divides by mitosis. | Embryo develops. |
| Ovule | Matures after fertilisation. | Seed forms. |
| Ovary | Wall and tissues develop. | Fruit forms. |
Language that earns precision
- pollen tube
- Tube growing from a pollen grain to deliver a male nucleus to an ovule.
- seed
- Mature ovule containing an embryo, food reserve and protective coat.
- fruit
- Mature ovary structure containing seeds.
- compatible
- Able to complete recognition and fertilisation within the species.
Common misconceptions
Claim: Pollen travels down the style as a whole grain.
Correction: A tube grows from it and carries male nuclei.
Claim: The pollen tube is a root.
Correction: It is a specialised outgrowth of a pollen grain.
Claim: The seed develops from the ovary.
Correction: An ovule becomes a seed; the ovary becomes a fruit.
Match the answer to the command word
Pollination → tube growth → nuclear fusion → seed and fruit.
Ovule becomes seed; ovary becomes fruit.
Recall, apply, then justify
Describe events from pollination to fertilisation in a flower.
Hint
Stigma, pollen tube, male nucleus, fusion.
Suggested marking points
- A compatible pollen grain lands on the stigma and germinates.
- A pollen tube grows down the style.
- A male gamete nucleus travels to an ovule.
- It fuses with the female gamete nucleus.
State the fate of the zygote, ovule and ovary after fertilisation.
Hint
Embryo, seed, fruit.
Suggested marking points
- The zygote develops into an embryo.
- The ovule develops into a seed.
- The ovary develops into a fruit.
Predict how blocking pollen-tube growth would affect fruit and seed formation.
Planning hint
Follow the sequence beyond the blocked step.
What a strong design includes
- The male nucleus would not reach the ovule.
- Gamete nuclei would not fuse.
- A zygote and embryo would not form.
- The ovule would not develop into a normal viable seed.
- Normal fertilisation-dependent fruit development may fail or be reduced.
- Pollination alone would therefore not guarantee seed production.