BiologyICSE Class 9 · Fertilisation

Pollen Tube, Double Fertilisation and Changes After Fertilisation (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

After pollination the pollen grain germinates on the stigma and a pollen tube grows down the style to the ovule, entering through the micropyle. One male gamete fuses with the egg (forming the zygote) and the other with the two polar nuclei (forming the endosperm nucleus): this is double fertilisation. The ovule becomes the seed and the ovary becomes the fruit.

Understand Pollen Tube, Double Fertilisation and Changes After Fertilisation

1. Germination of the pollen grain. A pollen grain that lands on a compatible stigma absorbs sticky fluid and swells. Its inner wall grows out as a *pollen tube*, which carries the tube nucleus and two male gametes down through the style, guided by chemicals from the ovule. The tube nucleus guides the tube and then degenerates.

2. The ovule and embryo sac. The ovule is attached to the ovary wall by a stalk (funicle); the opening in its coat is the *micropyle*. Inside lies the embryo sac with eight nuclei: the *egg cell* and two synergids near the micropyle, three antipodal cells at the far end and two *polar nuclei* in the centre.

3. Fertilisation. The pollen tube enters the ovule through the micropyle and bursts, releasing the two male gametes.

One male gamete fuses with the egg: *syngamy*, forming the diploid *zygote*.
The other fuses with the two polar nuclei: *triple fusion*, forming the *primary endosperm nucleus*, which grows into the nutritive endosperm.

Since two fusions take place, this is *double fertilisation*, found only in flowering plants.

4. Changes after fertilisation.

Zygote becomes the embryo (plumule, radicle, cotyledons).
Ovule becomes the seed; the integuments harden into the seed coat.
Ovary becomes the fruit; ovary wall becomes the pericarp.
Petals, sepals, stamens and often the style and stigma wither and fall.
A fruit formed only from the ovary is a true fruit; if other parts such as the thalamus also develop, it is a false fruit (for example apple).

5. Significance. Fertilisation restores the diploid number; the seed protects the embryo; fruits aid dispersal.

Pollen Tube, Double Fertilisation and Changes After Fertilisation: key facts

Pollen tube: Stigma
Style
Micropyle
Two male gametes
Tube nucleus
Double fertilisation: $M a l e g am e t e + e g g = z y g o t e ∣ M a l e g am e t e + tw o p o l a r n u c l e i = e n d os p er mn u c l e u s$
After fertilisation: Ovule becomes seed
Ovary becomes fruit
Zygote becomes embryo
Integuments become seed coat
Embryo sac: Egg cell
Two synergids
Three antipodals
Two polar nuclei

Pollen Tube, Double Fertilisation and Changes After Fertilisation in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

A delivery to an apartment

Suppose a courier has to deliver two parcels to one apartment: one for the owner and one for the shared storeroom, both entering through the same door.

Compare this with fertilisation.

Try it first, then show the solutionSolution

The courier is the pollen tube entering by the micropyle.
Two parcels are the two male gametes.
One goes to the egg, the other to the polar nuclei.

Answer: One door (micropyle), two parcels (gametes), two destinations.

Memory hook: Double delivery.

Tricks to remember Pollen Tube, Double Fertilisation and Changes After Fertilisation

Short memory aids. Say each one aloud once, then use it on a question the same day.

Z and E
Zygote from the egg; Endosperm from the polar nuclei.
Use it when: Double fertilisation.
O-S, O-F
Ovule to Seed, Ovary to Fruit.
Use it when: Post-fertilisation.

Pollen Tube, Double Fertilisation and Changes After Fertilisation: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Name the part · 2 marks · Short answerBoard level

Name the structure through which (a) the pollen tube enters the ovule, (b) the seed coat forms. [2]

Try it first, then show the solutionSolution

(a) Micropyle.
(b) Integuments.

Answer: (a) Micropyle (b) Integuments of the ovule.

Example 2: Why double · 3 marks · Short answerBoard level

Why is the fertilisation in flowering plants called double fertilisation? What does each fusion form? [3]

Try it first, then show the solutionSolution

Two fusions take place in the embryo sac.
Male gamete with egg forms the zygote.
Male gamete with polar nuclei forms the endosperm nucleus.

Answer: Two fusions: zygote and endosperm nucleus.

Example 3: Chromosome count · 3 marks · Short answerHarder board level

A plant has 24 chromosomes in a root cell. State the number in (a) the male gamete, (b) the zygote, (c) the primary endosperm nucleus. [3]

Try it first, then show the solutionSolution

Gametes are haploid: 12.
Zygote restores diploid: 24.
Endosperm nucleus has three haploid sets: 12 + 12 + 12 = 36.

Answer: (a) 12 (b) 24 (c) 36.

Example 4: Failure of tube · 3 marks · Short answerHarder board level

If the pollen tube fails to reach the micropyle, state three consequences. [3]

Try it first, then show the solutionSolution

No fertilisation.
The ovule does not become a seed.
The ovary may drop without forming a fruit.

Answer: No zygote, no seed and usually no fruit.

Example 5: Case: tomato flower · 5 marks · Case-basedHOTS / competency

Case. After pollination a tomato flower drops its petals while its ovary swells. (i) Which part becomes the fruit? [1] (ii) Which part becomes seeds? [1] (iii) What happens to the zygote? [1] (iv) Why do petals fall? [2]

Try it first, then show the solutionSolution

(i) Ovary.
(ii) Ovules.
(iii) It grows into the embryo.
(iv) They are no longer needed once pollination is done, so resources go to the fruit.

Answer: (i) Ovary (ii) Ovules (iii) Becomes embryo (iv) No longer needed after pollination.

Where students lose marks in Pollen Tube, Double Fertilisation and Changes After Fertilisation

The slips examiners see most often, and what to write instead.

Mistake: Writing that the ovary becomes the seed
Ovule and ovary are confused.
Do this: Ovule forms the seed; ovary forms the fruit.
Usually costs: 1 mark.
Mistake: Stating one male gamete only
Two male gametes are released.
Do this: Name both fusions.
Usually costs: 1 mark.
Mistake: Chromosome number errors for endosperm
Polar nuclei not counted.
Do this: Endosperm is triploid.
Usually costs: 1 mark.

Exam tips

Draw the labelled embryo sac with eight nuclei grouped as 3-2-3.
Write what each part becomes in a two-column table.
Use haploid and diploid terms correctly.
Mention the micropyle in pollen tube answers.

Practice questions on Pollen Tube, Double Fertilisation and Changes After Fertilisation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Triple fusion involves:
(a) egg + male gamete
(b) two polar nuclei + male gamete
(c) two male gametes
(d) two antipodals
Hint
Three nuclei.
Answer
(b).
Q2 · 1 mark · Very short answerBoard level
Name the part of the ovule through which the pollen tube enters. [1]
Hint
Opening.
Answer
Micropyle.
Q3 · 2 marks · Very short answerBoard level
What are the antipodal cells and where are they placed? [2]
Hint
Embryo sac.
Answer
Three cells at the end of the embryo sac away from the micropyle.
Q4 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Double fertilisation is found only in flowering plants.
Reason (R): Only flowering plants have an embryo sac with polar nuclei.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Polar nuclei.
Answer
(a).
Q5 · 3 marks · Short answerHarder board level
Differentiate a true fruit from a false fruit with one example of each. [3]
Hint
Thalamus.
Answer
A true fruit develops only from the ovary (mango); a false fruit also involves other parts such as the thalamus (apple).
Q6 · 2 marks · Very short answerHarder board level
Explain the role of the endosperm in a developing embryo. [2]
Hint
Food.
Answer
It stores food that nourishes the embryo as it grows.
Q7 · 3 marks · Short answerHarder board level
Trace the fate of the ovary wall, ovule and zygote in a pea flower. [3]
Hint
Pod.
Answer
Ovary wall becomes the pod, ovule becomes the seed, zygote becomes the embryo.
Q8 · 3 marks · Long answerHOTS / competency
Why is fertilisation without pollination impossible in a seed plant? Link the stages. [3]
Hint
Sequence.
Answer
Pollen must reach the stigma, germinate and form the pollen tube to carry gametes to the ovule; without pollination there is no tube and no fusion.
Q9 · 4 marks · Case-basedHOTS / competency
Case. In an experiment, the style of a flower is cut after pollination. (i) What is likely to happen to fertilisation? [2] (ii) Give reasons. [2]
Hint
Tube path.
Answer
(i) Fertilisation may fail. (ii) The pollen tube grows through the style; if the style is cut early, the tube cannot reach the ovule.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Entry point of pollen tube?Show answer
Micropyle.
2.Endosperm is formed by?Show answer
Fusion of a male gamete with two polar nuclei.
3.Ovary becomes?Show answer
Fruit.
4.Ovule becomes?Show answer
Seed.
5.Zygote ploidy?Show answer
Diploid.

Pollen Tube, Double Fertilisation and Changes After Fertilisation: frequently asked questions

Does the tube nucleus fuse?

No, it degenerates.

Which tissue feeds the embryo?

Endosperm or cotyledons.

What is syngamy?

Fusion of male gamete with egg.