Describe fertilisation as fusion of gamete nuclei
Distinguish contact, transfer and the actual nuclear event.
Section B15.2 · Sexual reproduction
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
Before you begin
- Recall DNA, inherited characteristics, nuclei and the distinction between growth and reproduction.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is fertilisation?
What you will learn
- Locate the defining event
- Avoid confusing earlier and later stages
Describe fertilisation as fusion of gamete nuclei
| Feature | Meaning |
|---|---|
| Contact | Gametes may be near or touching |
| Fertilisation | Gamete nuclei fuse |
| Pollination | Pollen transfer, not nuclear fusion |
| Later growth | Development after the reproductive event |
Locate the defining event
Fertilisation is fusion of the nuclei of gametes. Use nuclei in the definition rather than merely saying that two cells touch. A supplied sequence may show approach, contact, entry and nuclear fusion. The last of these establishes the defining event in this lesson; contact alone does not prove that fusion has occurred successfully.
The gamete nuclei carry inherited information. Their fusion forms the nucleus of the zygote. The surrounding cell structures and any later divisions have separate roles. Read the labels carefully: two nearby circles can represent nuclei still separate, while a later shared nucleus represents the supplied completed fusion. Diagram symbols are not direct measurements of microscopic timing.
Avoid confusing earlier and later stages
In a plant record, pollen transfer to a stigma is pollination, an earlier event distinct from fusion of gamete nuclei. A pollen grain arriving at a stigma does not by itself prove fertilisation. The plant pathway will later explain the intervening structures and processes. Here, use the supplied fusion statement rather than treating every transferred pollen grain as a zygote.
Fertilisation also differs from germination of a seed or growth of a young organism. Those later stages need their own evidence. A strong answer identifies which event the question actually supplies and gives the nuclear-fusion definition when asked. This foundation does not mark the separate plant reproduction, human anatomy or supervised practical sections as complete.
Sources for this lesson
Pause and explain
Does a contact-only photograph establish successful fertilisation?
Worked example
A sequence labels A as gametes touching and B as their nuclei fusing. Which establishes fertilisation?
Show the worked solution
- Contact alone is insufficient.
- B supplies nuclear fusion.
Answer B establishes fertilisation.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Define fertilisation precisely.
Give me a hint
Identify what fuses.
Compare my reasoning
- The reproductive cells are gametes.
- Their nuclei fuse.
Fertilisation is fusion of the nuclei of gametes.
Look for these in your work
- Name nuclei
- Name gametes
A record shows pollen moved from an anther to a stigma. Does it directly establish fertilisation?
Give me a hint
Separate transfer from nuclear fusion.
Compare my reasoning
- The event is pollen transfer.
- Gamete-nucleus fusion is not supplied.
No. The record establishes pollination, not the later fusion of gamete nuclei.
Look for these in your work
- Identify pollination
- State missing fusion evidence
A diagram shows two separate gamete nuclei after cell contact, then one combined zygote nucleus. Explain which stage establishes fertilisation.
Give me a hint
Read the nuclei rather than only the cell boundary.
Compare my reasoning
- The first stage keeps nuclei separate.
- The later stage supplies completed fusion.
The combined zygote-nucleus stage establishes the supplied nuclear fusion; the contact stage alone does not.
Look for these in your work
- Compare the nuclear stages
- Link the later stage to the definition
Common mistakes
- Defining fertilisation as contact only.
- Calling pollen transfer nuclear fusion.
What can you explain now?
Does a contact-only photograph establish successful fertilisation?
Compare with the explanation
No; nuclear fusion is not established
More event information is needed.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Define fertilisation and distinguish it from pollination and contact.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.