K325 / 2027

Lesson 7 of 12 / Reproduction

Fertilisation in flowering plants

How does a male nucleus reach a female gamete after pollen lands?

I can trace pollen-tube growth into an ovule and distinguish it from fertilisation.

  • I can trace pollen-tube growth and fertilisation.Syllabus

    Syllabus K325, Topic 13(n). Trace pollen-tube growth and fertilisation.

About 4 min

Make a guess. You are not marked.

A pollen grain lands on a stigma. How does its male nucleus reach the ovule deep inside the ovary?

  1. The whole grain rolls down into the ovary.
  2. Insects carry it down into the ovary.
  3. A pollen tube grows down the style.
Show the answer

A pollen tube grows down the style.

The grain germinates on the stigma and the tube carries the male nucleus to the ovule.

The key idea

A compatible pollen grain germinates on the stigma; its tube grows down the style into an ovule, delivering a male nucleus for fusion.

Pollination has transferred a pollen grain to the stigma. No gamete nuclei have fused yet.StigmaStyleOvaryOvule containsfemale gameteMicropyle
Pollination has transferred a pollen grain to the stigma. No gamete nuclei have fused yet.

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. 1

    Start at the stigma

    Do not start the pollen tube at the anther.

  2. 2

    Trace the tube

    It grows down the style towards an ovule and enters through the micropyle.

  3. 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.

Watch out for this

A student says: "The whole pollen grain travels down the style into the ovary." What is wrong with this?

Show the answer

The grain germinates on the stigma. A tube grows from it and carries the male nucleus towards the ovule.

Check your understanding

Which event directly forms a zygote in the ovule?

  1. The male and female gamete nuclei fuse.
  2. The petals open to expose the anthers.
  3. Pollen sticks to the stigma of the same species.
Show the answer

The male and female gamete nuclei fuse.

Nuclear fusion is fertilisation and restores the diploid state.

Exam-style questions

Check your understanding

After fertilisation, which part of a flower develops into the seed and which into the fruit?

  1. Ovule becomes the seed; ovary becomes the fruit
  2. Ovary becomes the seed; ovule becomes the fruit
  3. Petal becomes the seed; sepal becomes the fruit
  4. Anther becomes the seed; stigma becomes the fruit
Show the answer

Ovule becomes the seed; ovary becomes the fruit

The fertilised ovule develops into a seed, and the ovary wall develops into the fruit.

Quick recall

Card 1 of 3. Answer in your head, then check.

How does a male nucleus reach a female gamete after pollen lands?

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