Classify reproductive histories using nuclear events
Identify what the record establishes and what is missing.
Section 16.2 · Sexual reproduction
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
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
Which supplied event supports sexual reproduction?
What you will learn
- Compare origin evidence
- Keep uncertainty separate from a classification
Classify reproductive histories using nuclear events
Faithful vegetative copying supports asexual reproduction; gamete-nucleus fusion supports sexual reproduction; enlargement alone establishes growth. Original teaching model.
| Feature | Meaning |
|---|---|
| Vegetative copying | Asexual in the supplied no-mutation history |
| Nuclear fusion | Sexual in the supplied history |
| Enlargement alone | Growth only |
| Missing history | State the limit rather than inventing an origin |
Compare origin evidence
Compare three supplied histories: a rooted stem cutting with faithful copying, two gamete nuclei fusing to form a zygote, and a leaf expanding on an existing plant. The first supports asexual reproduction, the second supports sexual reproduction, and the third establishes growth only. They may all involve living cells, but their origin events differ.
A record can show genetically different offspring without describing the mechanism. That supports the supplied genetic difference, but is not alone a complete history of fertilisation. Mutations and other sources of variation also exist. Use the nuclear-fusion statement when it is supplied, rather than treating any difference as proof of sexual reproduction.
Keep uncertainty separate from a classification
Likewise, the word seed is not a universal substitute for an event history. Many familiar seeds follow fertilisation, but an unfamiliar record still needs its origin stated. A seed potato is a vegetative tuber planting term, not the fertilised ovule route. Do not turn a familiar name or storage shape into a complete reproductive diagnosis.
An evidence-based answer can state that information is insufficient. Name the missing observation, such as gamete-nucleus fusion or a documented vegetative origin, and avoid choosing a category from resemblance or proximity alone. This protects a useful definition from overgeneralisation while preparing learners for the more detailed plant and human reproductive pathways.
Pause and explain
What should an answer do when origin evidence is absent?
Worked example
A photograph shows two similar seedlings without any origin information. What additional record would establish the supplied sexual route?
Show the worked solution
- Resemblance does not show fusion.
- A reproductive record could show gamete-nucleus fusion and zygote formation.
Answer A supplied gamete-nucleus fusion and zygote-formation history.
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.
Classify a faithful-copying cutting, a gamete-fusion zygote and an enlarging leaf.
Give me a hint
Look at the supplied origin events.
Compare my reasoning
- Vegetative copying supports asexual reproduction.
- Fusion supports sexual reproduction; enlargement alone is growth.
Cutting: asexual. Gamete-fusion zygote: sexual. Enlarging leaf: growth only.
Look for these in your work
- Classify all three
- Use event evidence
Two descendants have a documented DNA difference but no reproductive history. Does the difference alone prove fertilisation?
Give me a hint
Variation and its origin are distinct.
Compare my reasoning
- The DNA difference is established.
- Its reproductive mechanism is not supplied.
No. A DNA difference alone does not establish fusion of gamete nuclei; the reproductive origin needs separate evidence.
Look for these in your work
- Retain the genetic observation
- State missing mechanism evidence
A seed potato grows from a supplied tuber bud while another record states gamete fusion before seed formation. Compare their routes.
Give me a hint
Use the organ and origin, not the shared word.
Compare my reasoning
- The tuber bud is vegetative.
- The other history supplies nuclear fusion.
The seed potato record is vegetative asexual propagation; the supplied gamete-fusion seed record is sexual reproduction.
Look for these in your work
- Distinguish the planting term
- Apply both event histories
Common mistakes
- Using genetic difference alone as a complete fusion history.
- Assuming every word seed denotes the same mechanism.
What can you explain now?
What should an answer do when origin evidence is absent?
Compare with the explanation
State the limit and name the missing information
Uncertainty is an evidence-based result.
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Make it stick
Classify three histories and explain when information is insufficient.
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.