Explain that new cells come from existing cells
Connect cell division with increases in cell number.
Core and Extended; Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall the distinction between plant, animal and bacterial cells. Read the supplied evidence before drawing a conclusion.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which event directly increases the number from one cell to two?
What you will learn
- State the origin of new cells.
- Use an ideal doubling model without confusing number with size.
Division is the source of new cells
New cells are produced by division of existing cells. One dividing cell can produce two daughter cells. This is different from one cell merely becoming larger: growth of an individual cell need not immediately increase the number of cells.
Division contributes to growth and repair in multicellular organisms. Before division, cell material and genetic information must be prepared for daughter cells. This lesson establishes the origin of cells; detailed mitosis and meiosis belong to later syllabus sections.
A calculation has stated assumptions
If every cell divides once in each round and none dies, the number doubles each round. Starting with three cells gives 3, 6, 12 and 24 after three rounds. Count rounds as transitions, not the number of entries in the sequence.
Real tissues do not necessarily divide synchronously; some cells stop dividing or die. The ideal arithmetic cannot predict a real tissue count without those assumptions. A new cell does not appear spontaneously from cell sap or from an empty space.
Pause and explain
Why can an ideal doubling prediction fail in a real tissue?
Worked example
Four cells each divide once in every round with no deaths. How many after three rounds?
Show the worked solution
- Round 1: 8.
- Round 2: 16.
- Round 3: 32.
Answer 32 cells.
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.
Two cells each divide once. How many result if none dies?
Give me a hint
Each original produces two.
Compare my reasoning
- 2 × 2 = 4.
- Count daughter cells, not division events.
4 cells.
Look for these in your work
- Correct doubling.
- Give cell count.
Five cells undergo two complete division rounds with no deaths. Calculate the final number.
Give me a hint
Double twice.
Compare my reasoning
- 5 → 10 → 20.
- There are two transitions.
20 cells.
Look for these in your work
- Two doublings.
- State the model assumptions.
A tissue has larger cells but the same number after treatment. Does this observation alone show cell division? Explain.
Give me a hint
Compare cell number and cell size.
Compare my reasoning
- The number has not increased.
- Larger cells indicate enlargement.
- The observation alone does not establish division; balanced division and loss would need further evidence.
No; enlargement alone does not prove division.
Look for these in your work
- Separate size from number.
- Avoid claiming no division could ever have occurred.
Common mistakes
- Division increases cell number; enlargement alone does not.
- Doubling requires all cells to divide and none to die in the model.
What can you explain now?
Where do new cells originate?
Compare with the explanation
From division of existing cells.
They do not form spontaneously from non-cellular material.
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Make it stick
Explain cell enlargement versus cell division using a counted example.
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.