The shape of the lesson
By the end of the lesson, learners can
- Copy, line up, separate: The sim cell has two pairs of chromosomes: red ones came from one parent and blue ones from the other.
- What mitosis is for: Mitosis makes more cells that are just like the parent cell.
- Stem cells: Extended.
- Mitosis = nuclear division giving genetically identical cells.
- Roles: growth, repair of damaged tissues, replacement of cells, asexual reproduction.
- Extended: exact replication first, then the copies separate, so the chromosome number is kept.
- Extended: stem cells are unspecialised and divide by mitosis to give cells that can specialise.
One picture every idea returns to
Mitosis is nuclear division giving rise to genetically identical cells. It is used for growth, repair of damaged tissues, replacement of cells and asexual reproduction. Extended: the chromosomes are replicated exactly before mitosis, and during mitosis the copies separate, so each daughter cell keeps the same chromosome number.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Two cells, identical copies.. Every time your body grows, heals a cut or replaces worn-out cells, it uses mitosis: a nuclear division that makes genetically identical cells. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Copy, line up, separate | The sim cell has two pairs of chromosomes: red ones came from one parent and blue ones from the other. Project tab 5 of the lab (Mitosis step by step) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: What mitosis is for | Mitosis makes more cells that are just like the parent cell. | Pairs |
| 21 to 30 min | Teach and check: Stem cells | Extended. | Anticipation / Reaction Guide |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 17 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Stem cells, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Anticipation / Reaction Guide
Before the lesson, students mark five statements true or false. After the teaching they mark them again and justify any change of mind in one sentence each. The statements come from the examiner traps below.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Mitosis does not halve the chromosome number. | A human body cell with 46 chromosomes gives two cells that each have 46, with exactly the same alleles. |
| Stem cells are not already specialised. | They become specialised only after dividing, when a daughter cell develops a particular structure and job. |
Mitosis: worksheet
6 questions, 17 marks. Written in the style of the papers; no past paper question is reproduced.
Describe what is meant by mitosis.
State four roles of mitosis in living organisms, with an example of each.
Extended. Explain how mitosis makes sure that each daughter cell has the same chromosomes as the parent cell.
Extended. The mass of DNA in the nucleus of a cell was measured over time. It was 6 arbitrary units at the start, rose to 12 units, and then fell to 6 units in each of the two new cells. (a) Explain why the mass of DNA doubled. (b) Explain why it then halved.
Extended. Describe stem cells and explain why they are useful in the body.
A gardener takes cuttings from one rose plant. Explain why all the new plants have flowers of exactly the same colour as the parent.
Answer key and marking notes
- Nuclear division (division of the nucleus).
- That gives rise to genetically identical cells.
- Growth, for example a zygote developing into an embryo.
- Repair of damaged tissues, for example healing a wound in the skin.
- Replacement of cells, for example replacing worn-out red blood cells.
- Asexual reproduction, for example potato tubers or strawberry runners.
- Before mitosis each chromosome is replicated exactly, making two identical copies.
- During mitosis the copies of each chromosome separate and move to opposite ends of the cell.
- So each daughter cell receives one copy of every chromosome, keeping the chromosome number (and the alleles) the same.
- (a) The chromosomes (DNA) were replicated exactly before mitosis.
- (b) During mitosis the copies separated into two nuclei, one for each new cell.
- So each new cell has the same mass of DNA (6 units) as the original cell.
- Stem cells are unspecialised cells.
- They divide by mitosis to produce daughter cells that can become specialised for specific functions.
- So they supply new cells for growth and to replace or repair tissues, for example new blood cells from bone marrow.
- The new plants are produced by asexual reproduction, so their cells are made by mitosis.
- Mitosis gives genetically identical cells, so the new plants have the same alleles as the parent.
8 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Which describes the cells produced by mitosis?
- Agenetically identical to each other and to the parent cell
- Bgenetically different from each other and from the parent cell
- Cidentical to each other but with half the parent's chromosomes
- Ddifferent from each other but with the parent's chromosome number
In which of these is mitosis NOT the main type of cell division?
- Apollen grains forming in an anther
- Ba broken bone being repaired
- Ca bean seedling growing taller
- Da spider plant producing plantlets on runners
Red blood cells live for about 120 days. Which role of mitosis is shown by the bone marrow making new red blood cells all the time?
- Areplacement of cells
- Basexual reproduction
- Cproduction of gametes
- Dgrowth of the embryo
A cell from a mouse has 40 chromosomes. It divides by mitosis twice. How many cells are produced, and how many chromosomes does each have?
- A4 cells, each with 40 chromosomes
- B4 cells, each with 10 chromosomes
- C2 cells, each with 20 chromosomes
- D4 cells, each with 80 chromosomes
Gardeners grow new African violet plants from small pieces of leaf. Why are all the new plants the same flower colour as the parent?
- ATheir cells are produced by mitosis, so they have the same alleles
- BTheir cells are produced by meiosis, so they have the same alleles
- CLeaf cells contain only the gene for flower colour
- DFlower colour is not controlled by genes
The graph shows the mass of DNA in a cell during one cell cycle that ends in mitosis. What happens at A and at B?
- AA: chromosomes replicate; B: the copies separate into two cells
- BA: the copies separate; B: chromosomes replicate
- CA: meiosis halves the DNA; B: fertilisation doubles it
- DA: the cell absorbs DNA from food; B: DNA is broken down
Which statement about stem cells is correct?
- AThey are unspecialised and divide to form cells that can become specialised
- BThey are specialised cells that can change into any other specialised cell
- CThey divide by meiosis to produce new body cells
- DThey are found only in plants, at root and shoot tips
Why must the chromosomes be replicated exactly before mitosis?
- ASo each daughter cell receives a complete set of identical genes
- BSo the daughter cells have twice as many chromosomes as the parent
- CSo the daughter cells are genetically different from each other
- DSo the parent cell can stay alive after it has divided
Quiz key
Mitosis is nuclear division giving genetically identical cells, with the same chromosomes as the parent cell. Genetically different cells are produced by meiosis. Halving the chromosome number is also a feature of meiosis, not mitosis. Cells from mitosis are not genetically different from each other.
Pollen grains carry male gametes, so their formation involves meiosis. Bone repair, the growth of a seedling and asexual reproduction by runners all need genetically identical cells, so they use mitosis.
Worn-out red blood cells are replaced by new ones made by cell division in the bone marrow: replacement of cells. Asexual reproduction makes a new organism, not new cells within one. Gametes are made by meiosis. The adult is not growing; the number of red blood cells stays about the same.
One cell gives 2, and each of those gives 2, so 4 cells; mitosis keeps the chromosome number the same, so each has 40. Dividing the chromosome number (to 10 or 20) is what happens in meiosis, and only once, not at each mitosis. The chromosomes are copied before division but the copies separate, so the number never doubles to 80 in the daughter cells.
Asexual reproduction uses mitosis, which gives genetically identical cells, so the new plants have exactly the parent's alleles, including those for flower colour. Meiosis gives genetically different cells. Leaf cells contain all the plant's genes, not just one. Flower colour is controlled by genes, which is why it is passed on.
At A the mass doubles from 10 to 20 units, because each chromosome is replicated exactly before mitosis. At B it falls back to 10 because the copies separate and go to two daughter cells. Reversing the order would mean the copies separate before they exist. This cycle has no meiosis or fertilisation. Cells copy their own DNA; they do not take it in from food, and it is shared out, not broken down.
Stem cells are unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions. Stem cells are not already specialised. They divide by mitosis, not meiosis, which only makes gametes. Animals have stem cells too, for example in embryos and in bone marrow.
Exact replication makes two identical copies of every chromosome; when the copies separate, each daughter cell gets one copy of each, so it has the same genes and chromosome number as the parent. The number is not doubled in the daughter cells. Exact copying makes the cells identical, not different. The parent cell does not survive alongside its daughters: it becomes them.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.