Explain the role of mitosis in growth of multicellular organisms
Completed mitotic cell cycles can increase cell number during growth. The invented one-cell lineage doubles to eight after three stated rounds, adding seven cells.
Section B16.2 · Cell division
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-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. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Recall chromosomes, genes, chromosome sets, selective gene expression and the distinction between a nucleus and a whole cell.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
How does normal completed mitotic division contribute to growth?
What you will learn
- Connect growth with increased cell number
- Keep growth models conditional
Original teaching model. Counts and records are stipulated; drawings are schematic.
| Feature | Meaning |
|---|---|
| Role | More cells contribute to multicellular growth |
| Model rounds | 0, 1, 2 and 3 |
| Model totals | 1, 2, 4 and 8 cells |
| Limit | No timing or universal growth-rate prediction |
Connect growth with increased cell number
Mitosis contributes to growth by allowing dividing cells to produce daughter cells with the same genetic information. After normal nuclear division and subsequent cell division, one cell gives two, increasing the cell number by one. In a growing multicellular organism, many such events can build tissues containing more cells while preserving the chromosome complement in each product.
Growth of an organism is not explained only by mitosis. Cells may also enlarge, synthesise material and become specialised, and tissues must organise those products. A cell increasing its volume is not itself evidence that mitosis occurred. To explain the specified mitotic contribution, connect complete division with more cells rather than treating every increase in mass as a nuclear event.
Keep growth models conditional
An invented lineage starts with one cell and states that every cell completes division once per round, with no loss. Its counts are one, two, four and eight across rounds zero to three. These numbers describe the stipulated pattern, not the timing or growth rate of an actual embryo, plant or tissue. Different cells need not divide together or at a constant rate.
For this model, three rounds are not three individual divisions. The successive rounds contain one, two and four completed division events, adding seven cells to the original one. Label a round, an event, a total population and a net increase separately. Such arithmetic is useful only when the biological assumptions are supplied; normal mitosis does not imply unlimited exponential growth.
Sources for this lesson
Pause and explain
One starting cell undergoes three stipulated doubling rounds. What is the final count?
Worked example
One cell completes three whole-population rounds with no loss. What is the final count?
Show the worked solution
- Double at each stated round.
- Distinguish total from increase.
Answer The count is eight cells, a net increase of seven.
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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.
Explain the mitotic contribution to multicellular growth.
Give me a hint
Connect nuclear division with completed daughter cells.
Compare my reasoning
- Describe genetic information preserved in daughter nuclei.
- Connect subsequent cell division with more cells.
Normal mitosis followed by cell division produces additional cells with the same genetic information, contributing to growth.
Look for these in your work
- Preserve the chromosome information
- Explain increased cell number
One cell completes three synchronous no-loss rounds. Calculate the final total and net increase.
Give me a hint
Use the sequence one, two, four, eight.
Compare my reasoning
- Double three times.
- Subtract the initial cell from the final total.
The final total is eight cells and the net increase is seven cells.
Look for these in your work
- State the doubling assumptions
- Separate total and increase
A tissue gains mass, but no cell-count or nuclear-division evidence is supplied. Can its mass change alone establish mitosis?
Give me a hint
Consider cell enlargement and synthesis.
Compare my reasoning
- Identify the observed mass change.
- State that division evidence is missing.
No. Increased mass can involve enlargement or synthesis; cell-number and nuclear-division evidence are needed to establish the mitotic contribution.
Look for these in your work
- Use the observed quantity
- Avoid an unsupported mechanism claim
Common mistakes
- Cell enlargement is not itself mitosis.
- Synchronous no-loss doubling is a stated model, not a universal growth rate.
What can you explain now?
One starting cell undergoes three stipulated doubling rounds. What is the final count?
Compare with the explanation
Eight cells
The counts are one, two, four and eight.
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Make it stick
Without your notes, connect growth with increased cell number and keep growth models conditional. Distinguish nuclear division, chromosome copies and completed daughter cells 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.