Lesson 7 of 12 / Reproduction
Fertilisation in flowering plants
How does a male nucleus reach a female gamete after pollen lands?
In this lesson: Trace pollen-tube growth into an ovule and distinguish it from fertilisation.
About 4 min
The key ideaA compatible pollen grain germinates on the stigma; its tube grows down the style into an ovule, delivering a male nucleus for fusion.
Nuclei and the ovule opening are enlarged for clarity. Endosperm formation is outside this outcome.
Explanation
After compatible pollen reaches a stigma, the pollen grain germinates and grows a pollen tube. The tube extends through the style towards the ovary.
A male gamete nucleus travels within the pollen tube. The tube grows towards an ovule and enters through a small opening, the micropyle, so the male nucleus can reach the female gamete.
The male and female gamete nuclei fuse, forming a diploid zygote. This is fertilisation. Pollination only moved pollen to the stigma; pollen-tube growth delivered the nucleus to the site of fusion.
The ovule can develop into a seed and the ovary into a fruit after fertilisation. Detailed seed development and endosperm formation are outside this outcome; focus on the route and the fusion event.
Step by step
- 1
Start at the stigma
Do not start the pollen tube at the anther.
- 2
Trace the tube
It grows down the style towards an ovule and enters through the micropyle.
- 3
Name the fusion
The male nucleus fuses with the female nucleus to form a zygote.
Worked example
A tube but no fusion yet
A pollen tube is halfway down the style. Has fertilisation necessarily occurred?
One way to explain it
No. The male nucleus has not yet reached the female gamete inside an ovule. Fertilisation occurs only when the two gamete nuclei fuse.
Why this answer works
- Locate the female gamete inside an ovule.
- Tube growth and nuclear fusion are separate events.
Is this true? "The whole pollen grain travels down the style into the ovary."
The grain germinates on the stigma. A tube grows from it and carries the male nucleus towards the ovule.