Pollination only delivers the pollen to the stigma. The male gamete still has to reach the ovule hidden inside the ovary, and the seed that forms will only start to grow when the conditions are right. The growth of the pollen tube is Extended content.
Fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule. Extended: after pollination a pollen tube grows out of the pollen grain, down through the style to an ovule, and enters it through the micropyle, carrying the pollen nucleus. Seeds need water, oxygen and a suitable temperature to germinate.
Fig. 1: germination experiment; only tube A has water, oxygen and a suitable temperature
Section 01
The pollen tube and fertilisation.
Extended. Press Land a pollen grain in the lab and follow it. Watch the stage and nuclei readings change as the pollen tube grows through the style and into the ovule.
Pollination: the pollen grain lands on the sticky stigma.
Pollen tube (Extended): a tube grows out of the pollen grain and down through the style towards an ovule, carrying the pollen nucleus at its tip.
Entry (Extended): the tube enters the ovule through a small hole, the micropyle.
Fertilisation: the pollen nucleus fuses with a nucleus in the ovule, forming a zygote. (Both gamete nuclei are haploid; the zygote nucleus is diploid.)
Afterwards: the fertilised ovule develops into a seed and the ovary into a fruit.
Examiner trap
Pollination and fertilisation are different events. Pollination is pollen landing on the stigma; fertilisation happens later, inside the ovule, when the nuclei fuse. A pollen grain does not travel down the style: its tube grows down, carrying the nucleus.
Section 02
Conditions for germination.
Four tubes of seeds are set up, each missing one condition except the control A. Press Leave for 5 days and read the table. Then change the temperature of tube A with the slider and run it again.
Tube
Conditions
Missing
Germinated
A
damp cotton wool, air, 20 °C
nothing (control)
4 of 4
B
dry cotton wool, air, 20 °C
water
0 of 4
C
boiled water with an oil layer, 20 °C
oxygen
0 of 4
D
damp cotton wool, air, fridge at 4 °C
suitable temperature
0 of 4
Water: lets the seed swell and activates its enzymes, which break down stored food for growth.
Oxygen: needed for aerobic respiration, which releases energy for growth. Boiling removes dissolved oxygen and the oil stops more dissolving.
Suitable temperature: enzymes work slowly in the cold and are denatured if it is too hot. In the lab, tube A germinates fully at about 20 to 30 °C, less at 10 or 15 °C, and not at all at 5 °C or below or at 45 °C or above.
Fair test: same type and number of seeds in each tube; change one condition only; tube A is the control.
Examiner trap
Light is not one of the conditions needed for germination: the seed uses its food store, not photosynthesis. Do not add light, carbon dioxide or soil to your list.
Stage 1 · Learn
Check what the sim just showed you
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Quick check+10 XP
Extended: in the pollen tube tab, how does the pollen tube enter the ovule?
Quick check+10 XP
What does the nuclei reading show at the end of the pollen tube run?
Quick check+10 XP
In the germination tab at 20 °C, which tube is the only one where seeds germinate?
Quick check+10 XP
Tube C uses boiled water covered with a layer of oil. Which condition does this remove?
Stage 2 · Exam
Exam-style questions
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Finish the four checks above to unlock the exam questions
Exam style+20 XP
Which describes fertilisation in a flowering plant?
Exam style+20 XP
Extended: which is the correct order of events?
Exam style+20 XP
Why do seeds kept in a fridge at 4 °C not germinate, even with water and air?
Exam style+20 XP
Why do germinating seeds need oxygen?
Skill unlocked
Fertilisation and germination, mastered.
This skill is now recorded on your profile. Keep the chain going.