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Ordinary Level Revision Notes
Leaving Cert Ordinary Level Biology
Chapter 10: Cell Division and the Cell Cycle
Mitosis, Meiosis & Cancer
Subtopics Covered
- Learning Outcomes
- Big Picture: Why Cell Division Matters
- Key Terms
- The Cell Cycle
- Mitosis: Definition and Function
- The Four Main Stages of Mitosis
What This Pack Includes
- Structured chapter notes formatted for ExamsLogic website reading
- Exam-focused diagrams, definitions, and worked examples
- Interactive practice sections carried over from the source notes
- Independent study guidance based on the official curriculum
- Print-friendly layout for future PDF export when needed
This publication is an independent educational resource developed by ExamsLogic and compiled by experienced educators. It is based on publicly available official curricula, including Cambridge, Pearson Edexcel, IB, and the Irish Leaving Certificate. This product is not endorsed by, affiliated with, or sponsored by any examination board or governing authority. All registered trademarks remain the property of their respective owners.
1. Learning Outcomes
- Explain why cells divide in living organisms.
- Describe the cell cycle, including interphase and nuclear division.
- Describe the four main stages of mitosis: prophase, metaphase, anaphase and telophase.
- State the functions of mitosis: growth, repair and asexual reproduction.
- Explain the purpose of meiosis in gamete formation.
- Understand chromosome reduction from diploid to haploid, written as 2n → n.
- Explain how meiosis helps introduce genetic variation.
- Define cancer and distinguish between benign and malignant tumours.
- Give examples of carcinogens and describe how they may increase cancer risk.
OL Focus: You do not need extremely detailed chromosome behaviour, but you must know the purpose, outcomes and key differences between mitosis and meiosis.
2. Big Picture: Why Cell Division Matters
Growth
New cells are made so a young organism can grow larger.
Repair
Damaged cells can be replaced after injury or normal wear.
Reproduction
Some organisms reproduce asexually using mitosis, while animals and plants make gametes using meiosis.
Biology link: Cell division must be carefully controlled. If control is lost, cells may divide too quickly and form a tumour.
3. Key Terms
| Term | Meaning | Exam detail |
|---|---|---|
| Cell cycle | The sequence of growth, preparation and division in a cell. | Includes interphase and division. |
| Interphase | The stage when a cell grows and copies its DNA. | It is not a resting stage; the cell is active. |
| Nuclear division | Division of the nucleus. | Mitosis and meiosis are types of nuclear division. |
| Chromosome | A structure made from DNA carrying genetic information. | Chromosomes become visible during cell division. |
| Diploid | A cell with two sets of chromosomes. | Written as 2n. |
| Haploid | A cell with one set of chromosomes. | Written as n. Gametes are haploid. |
| Tumour | A mass of abnormal cells. | May be benign or malignant. |
| Carcinogen | A cancer-causing agent. | Examples include tobacco smoke and UV radiation. |
Common Mistake: Saying interphase is “when nothing happens.” Actually, the cell grows, carries out normal activities and copies its DNA.
4. The Cell Cycle
The cell cycle is the ordered sequence of events by which a cell grows, prepares for division and divides.
| Stage | What happens? | Why it matters |
|---|---|---|
| Interphase | The cell grows, makes organelles and copies DNA. | Prepares the cell for division. |
| Nuclear division | The nucleus divides by mitosis or meiosis. | Genetic information is shared into new nuclei. |
| Cytokinesis | The cytoplasm divides. | New cells separate fully. |
Examiner Trap: DNA copying happens before mitosis, during interphase. Do not say chromosomes are copied during anaphase.
5. Mitosis: Definition and Function
Mitosis is nuclear division that produces two genetically identical daughter cells with the same chromosome number as the parent cell.
Parent cell→
DNA copied→
Nucleus divides→
Two identical cells
| Function of mitosis | Explanation | Example |
|---|---|---|
| Growth | Increases the number of cells. | A child growing taller. |
| Tissue repair | Replaces damaged or worn-out cells. | Healing a cut. |
| Asexual reproduction | Produces genetically identical offspring. | Some simple organisms and plant cuttings. |
Examiner Secret: In mitosis answers, the phrases “two daughter cells”, “genetically identical” and “same chromosome number” are high-value marking points.
6. The Four Main Stages of Mitosis
| Stage | What happens? | Simple memory clue |
|---|---|---|
| Prophase | Chromosomes become visible. The nuclear membrane begins to break down. | Prepare |
| Metaphase | Chromosomes line up across the middle of the cell. | Middle |
| Anaphase | Chromatids are pulled apart to opposite ends of the cell. | Apart |
| Telophase | New nuclei form. The cell prepares to split into two cells. | Two nuclei |
Exam Tip: For Ordinary Level, a simple labelled diagram of PMAT is often enough if your explanation clearly states what happens at each stage.
7. Mitosis Outcome Diagram
8. Meiosis: Definition and Function
Meiosis is nuclear division that produces gametes with half the chromosome number of the parent cell.
Diploid parent cell → Haploid gametes
2n → n
2n → n
| Feature | Meiosis detail | Why it matters |
|---|---|---|
| Purpose | Formation of gametes. | Gametes are needed for sexual reproduction. |
| Chromosome number | Reduced from 2n to n. | Prevents chromosome number doubling every generation. |
| Genetic variation | Gametes are not genetically identical. | Offspring show variation. |
| Examples of gametes | Sperm and egg cells. | They fuse during fertilisation. |
Examiner Trap: Meiosis does not make body cells for growth. It makes gametes for sexual reproduction.
9. Meiosis Outcome Diagram
Examiner Secret: The key Ordinary Level idea is simple: meiosis halves chromosome number and produces variation.
10. Mitosis vs Meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Main purpose | Growth, repair and asexual reproduction. | Gamete formation for sexual reproduction. |
| Number of daughter cells | Two. | Four. |
| Chromosome number | Same as parent cell. | Half the parent cell. |
| Symbol | 2n → 2n | 2n → n |
| Genetic similarity | Genetically identical. | Genetically different. |
| Variation | Does not normally introduce variation. | Introduces genetic variation. |
Exam Tip: In comparison questions, use matched pairs. For example, “mitosis produces two cells; meiosis produces four cells.”
11. Cancer: Definition and Cell Division Link
Cancer is a disease caused by uncontrolled cell division. The abnormal cells may form a mass called a tumour.
DNA damage→
Control lost→
Rapid cell division→
Tumour may form
| Term | Meaning | Exam detail |
|---|---|---|
| Cancer | Uncontrolled cell division. | Cells divide when they should not. |
| Tumour | A mass of abnormal cells. | Can be benign or malignant. |
| Metastasis | Spread of cancer cells to other parts of the body. | Associated with malignant tumours. |
Common Mistake: Not all tumours are cancerous. Benign tumours do not invade nearby tissues or spread around the body.
12. Benign vs Malignant Tumours
| Feature | Benign tumour | Malignant tumour |
|---|---|---|
| Cancerous? | Usually non-cancerous. | Cancerous. |
| Growth | May grow slowly and remain in one place. | May grow quickly and invade tissues. |
| Spread | Does not normally spread to other body parts. | Can spread through blood or lymph. |
| Danger | May still cause problems by pressing on organs. | More dangerous because it can invade and spread. |
Examiner Trap: “Malignant” means cancerous and capable of invading/spreading. “Benign” means non-cancerous or not spreading, but it can still be medically serious depending on location.
13. Causes of Cancer and Carcinogens
A carcinogen is an agent that increases the risk of cancer by damaging DNA or interfering with normal cell control.
| Carcinogen / risk factor | Example | How it may increase cancer risk |
|---|---|---|
| Tobacco smoke | Cigarettes and second-hand smoke. | Contains chemicals that can damage DNA. |
| UV radiation | Strong sunlight or sunbeds. | Can damage skin cell DNA. |
| Ionising radiation | X-rays at high or repeated doses. | Can damage DNA in cells. |
| Certain viruses | Some viruses are linked with cancer risk. | May affect cell control mechanisms. |
| Some chemicals | Asbestos and some industrial chemicals. | Can irritate tissues or damage DNA. |
Exam Tip: A question may ask for examples of carcinogens. Give named examples such as tobacco smoke, UV radiation or asbestos.
Examiner Secret: Cancer is not caused by mitosis itself. Normal mitosis is essential. Cancer happens when the control of cell division is lost.
14. Interactive Simulator: Cell Division Detective
Identify the Process
Clue: Produces two genetically identical cells.
Feedback
Ready
Look for cell number, chromosome number and whether division is controlled.
15. Interactive Simulator: PMAT Stage Checker
Choose the Stage
Description: Chromosomes line up in the middle of the cell.
Feedback
PMAT
Use the memory clues: Prepare, Middle, Apart, Two nuclei.
16. High-Value Exam Guidance
Exam Tip 1: For mitosis, always include “two genetically identical daughter cells.”
Exam Tip 2: For meiosis, always include “gametes” and “halves chromosome number.”
Exam Tip 3: In cancer questions, link cancer to uncontrolled cell division.
Examiner Trap 1: Do not say meiosis is for growth. Mitosis is for growth.
Examiner Trap 2: Do not say all tumours spread. Malignant tumours can spread; benign tumours usually do not.
Examiner Trap 3: Do not confuse chromosome number with number of cells.
Common Mistake 1: Saying mitosis produces four cells. Correct: mitosis produces two cells.
Common Mistake 2: Saying meiosis produces identical cells. Correct: meiosis produces genetically different gametes.
Examiner Secret 1: “2n → n” is a compact way to show chromosome reduction in meiosis.
Examiner Secret 2: Carcinogens increase cancer risk; they do not guarantee that cancer will happen.
17. MCQs with Instant Answers
1. What happens during interphase?
Answer: A. During interphase, the cell grows, makes organelles and copies DNA.
2. Mitosis produces:
Answer: B. Mitosis produces two genetically identical daughter cells.
3. In metaphase, chromosomes:
Answer: A. Metaphase means chromosomes line up across the middle.
4. Meiosis is important because it:
Answer: B. Meiosis produces haploid gametes and introduces genetic variation.
5. Which symbol represents chromosome reduction in meiosis?
Answer: C. Meiosis reduces chromosome number from diploid to haploid, 2n → n.
6. Cancer is best described as:
Answer: B. Cancer involves uncontrolled cell division.
7. Which one is a carcinogen?
Answer: A. Tobacco smoke contains chemicals that can increase cancer risk.
8. A malignant tumour:
Answer: C. Malignant tumours are cancerous and can spread.
18. Structured Exam Questions
- Define the cell cycle and name two main events that occur during interphase. [4]
- State three functions of mitosis. [3]
- Describe the four stages of mitosis using the terms prophase, metaphase, anaphase and telophase. [8]
- Explain why meiosis is important in sexual reproduction. [5]
- Compare mitosis and meiosis under four headings. [8]
- Define cancer and explain how it is linked to cell division. [4]
- Distinguish between benign and malignant tumours. [4]
- Name two carcinogens and explain what a carcinogen is. [4]
19. Detailed Mark Scheme
Q1. Cell cycle is the sequence of events by which a cell grows, prepares and divides [2]. Interphase: cell growth [1], DNA copied [1], organelles made/normal cell activities [1]. Max 4.
Q2. Growth [1], tissue repair/replacement of damaged cells [1], asexual reproduction [1].
Q3. Prophase: chromosomes become visible/nuclear membrane breaks down [2]. Metaphase: chromosomes line up in middle [2]. Anaphase: chromatids/chromosomes pulled apart to opposite ends [2]. Telophase: new nuclei form/cell prepares to divide [2].
Q4. Meiosis produces gametes [1]. Gametes are haploid [1]. Chromosome number is reduced from 2n to n [1]. Fertilisation restores diploid number [1]. Meiosis introduces genetic variation [1].
Q5. Mitosis: two cells [1], same chromosome number [1], genetically identical [1], growth/repair/asexual reproduction [1]. Meiosis: four cells [1], half chromosome number [1], genetically different [1], gamete formation [1].
Q6. Cancer is uncontrolled cell division [2]. It occurs when normal control of the cell cycle/division is lost [1], producing abnormal cells/tumour [1].
Q7. Benign tumour is usually non-cancerous/does not spread [2]. Malignant tumour is cancerous/can invade tissues and spread [2].
Q8. Carcinogen is a cancer-causing agent or factor that increases cancer risk [2]. Examples: tobacco smoke [1], UV radiation [1], ionising radiation/asbestos/certain chemicals [1]. Max 4.
Q2. Growth [1], tissue repair/replacement of damaged cells [1], asexual reproduction [1].
Q3. Prophase: chromosomes become visible/nuclear membrane breaks down [2]. Metaphase: chromosomes line up in middle [2]. Anaphase: chromatids/chromosomes pulled apart to opposite ends [2]. Telophase: new nuclei form/cell prepares to divide [2].
Q4. Meiosis produces gametes [1]. Gametes are haploid [1]. Chromosome number is reduced from 2n to n [1]. Fertilisation restores diploid number [1]. Meiosis introduces genetic variation [1].
Q5. Mitosis: two cells [1], same chromosome number [1], genetically identical [1], growth/repair/asexual reproduction [1]. Meiosis: four cells [1], half chromosome number [1], genetically different [1], gamete formation [1].
Q6. Cancer is uncontrolled cell division [2]. It occurs when normal control of the cell cycle/division is lost [1], producing abnormal cells/tumour [1].
Q7. Benign tumour is usually non-cancerous/does not spread [2]. Malignant tumour is cancerous/can invade tissues and spread [2].
Q8. Carcinogen is a cancer-causing agent or factor that increases cancer risk [2]. Examples: tobacco smoke [1], UV radiation [1], ionising radiation/asbestos/certain chemicals [1]. Max 4.
20. Mastery Checklist
- I can define the cell cycle.
- I can explain what happens during interphase.
- I can state the functions of mitosis.
- I can describe prophase, metaphase, anaphase and telophase.
- I can explain that mitosis produces two genetically identical cells.
- I can explain that meiosis produces gametes.
- I can use 2n → n to describe chromosome reduction in meiosis.
- I can compare mitosis and meiosis clearly.
- I can define cancer as uncontrolled cell division.
- I can distinguish between benign and malignant tumours.
- I can give examples of carcinogens.
- I can answer Ordinary Level exam questions using correct biological terms.