Describe a haploid nucleus as one chromosome set
Haploid means one chromosome set. A three-type model has three chromosomes in one set; usual human model gametes have 23 individual chromosomes, not pairs.
Exam scope and assessment notes
Extended only (Supplement) · 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 the nucleus, DNA base pairing, gametes, fertilisation, enzymes, membrane carriers and chemical synapses.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What defines a haploid nucleus?
What you will learn
- Define haploid using sets rather than one chromosome
- Read one representative of each supplied chromosome type
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Definition | One chromosome set |
| Stipulated n = 3 | Three individuals, one of each supplied type |
| Stipulated n = 5 | Five individuals in one set |
| Human gamete model | 23 chromosomes, not 23 pairs |
Define haploid using sets rather than one chromosome
A haploid nucleus contains a single set of chromosomes. One set does not mean one chromosome: the set can contain several different chromosome types. In a stipulated model with three types, a haploid nucleus has one representative of type 1, one of type 2 and one of type 3, giving three chromosomes in that single set.
The number in one set is commonly written n. If n = 3 in the supplied model, the haploid total is 3; if another model has n = 5, its haploid total is 5. Species and models can have different set sizes, so the word haploid alone does not supply a universal chromosome total for every organism.
Read one representative of each supplied chromosome type
Human gametes in the usual syllabus model have one set of 23 chromosomes. That is 23 individual chromosomes, not 23 pairs. An X-bearing or Y-bearing sperm still has the one-set total under this model; changing which sex chromosome is present does not change the total to two chromosome sets.
The original three-type diagram uses one labelled rod per supplied type. The rods represent stipulated individual, unreplicated chromosomes rather than DNA strands or a measured human karyotype. Use the key to count both set number and total number, and avoid assigning a cell’s ploidy solely from an unlabelled collection of rods.
Pause and explain
A supplied model has n = 5. What is the haploid total?
Worked example
A model has n = 3. How can one haploid set contain three chromosomes?
Show the worked solution
- Identify one representative of each of three types.
- Distinguish a set from one object.
Answer The single set contains one chromosome of each of the three supplied types, so it contains three chromosomes rather than one.
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 a haploid nucleus and explain why it need not contain one chromosome.
Give me a hint
Use one set containing several types.
Compare my reasoning
- Give the single-set definition.
- Allow one representative of multiple supplied types.
A haploid nucleus contains one chromosome set; if the set has several types, it contains several chromosomes, not just one.
Look for these in your work
- Define one set
- Distinguish set and total
Calculate the haploid total for stipulated set size n = 5.
Give me a hint
One set has the stated n chromosomes.
Compare my reasoning
- Use the supplied set size of five.
- Keep the total as individual chromosomes rather than pairs.
The haploid total is five individual chromosomes in one set.
Look for these in your work
- Use n correctly
- Label individual chromosomes
Compare X-bearing and Y-bearing human sperm totals in the usual model.
Give me a hint
The alternative sex-chromosome label does not double the set.
Compare my reasoning
- Retain one set of 23 in either sperm.
- Distinguish the sex-chromosome alternative from total count.
Both model sperm types have 23 individual chromosomes in one set; one includes X and the other Y as the sex-chromosome contribution.
Look for these in your work
- Keep both totals at 23
- Distinguish type and set number
Common mistakes
- Haploid does not mean one chromosome.
- A human model gamete has 23 chromosomes, not 23 pairs.
What can you explain now?
A supplied model has n = 5. What is the haploid total?
Compare with the explanation
Five individual chromosomes
One set contains five specified types.
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Make it stick
Explain define haploid using sets rather than one chromosome and read one representative of each supplied chromosome type. Use the stated cell, chromosome sets and information pathway before opening the solutions.
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.