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Ordinary Level Revision Notes
Leaving Cert Ordinary Level Biology
Chapter 6: Cell Structure and Microscopy
Study Leaving Cert Ordinary Level Biology Cell Structure and Microscopy with ExamsLogic revision notes, diagrams, summaries, and exam-focused practice.
Subtopics Covered
- Chapter Overview
- Learning Outcomes
- Cell Theory and Organisation
- Main Cell Structures and Functions
- Plant Cell and Animal Cell Comparison
- Prokaryotic and Eukaryotic Cells
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. Chapter Overview
Cells are the basic units of life. This chapter explains the structures found in plant and animal cells, compares prokaryotic and eukaryotic cells, and explains how microscopes and stains are used to observe cells.
ExamsLogic Big Idea: Cell structure is always linked to function. If you know what a part does, you can remember why it is there.
2. Learning Outcomes
- I can identify main structures of plant and animal cells.
- I can state the function of each cell structure.
- I can compare plant and animal cells.
- I can compare prokaryotic and eukaryotic cells.
- I can describe how a light microscope is used.
- I can explain why iodine and methylene blue stains are used.
- I can compare light microscopes with electron microscopes.
3. Cell Theory and Organisation
All living organisms are made of cells. A cell is the smallest unit of life that can carry out life processes.
| Term | Meaning | Example |
|---|---|---|
| Cell | Basic unit of life. | Cheek cell, onion cell. |
| Tissue | Group of similar cells working together. | Muscle tissue. |
| Organ | Different tissues working together. | Heart, leaf. |
| Organ system | Organs working together. | Digestive system. |
4. Main Cell Structures and Functions
| Structure | Found in | Function |
|---|---|---|
| Cell membrane | Plant and animal cells | Controls movement of substances in and out. |
| Cell wall | Plant cells, bacteria, fungi | Supports and strengthens the cell. |
| Nucleus | Plant and animal cells | Controls cell activities and contains genetic material. |
| Cytoplasm | Plant and animal cells | Site of many chemical reactions. |
| Mitochondria | Plant and animal cells | Site of aerobic respiration and energy release. |
| Chloroplasts | Green plant cells | Site of photosynthesis; contain chlorophyll. |
| Ribosomes | Plant, animal and bacterial cells | Site of protein synthesis. |
| Vacuole | Large permanent vacuole in plant cells | Stores cell sap and helps support the cell. |
Examiner Tip: In cell questions, name the structure and state its function clearly.
5. Plant Cell and Animal Cell Comparison
| Feature | Plant Cell | Animal Cell |
|---|---|---|
| Cell membrane | Present | Present |
| Cell wall | Present | Absent |
| Nucleus | Present | Present |
| Cytoplasm | Present | Present |
| Mitochondria | Present | Present |
| Chloroplasts | Often present in green parts | Absent |
| Large vacuole | Usually present | Absent or small temporary vacuoles |
| Shape | More regular/box-like | More irregular/rounded |
Examiner Trap: Not all plant cells contain chloroplasts. Root cells usually do not photosynthesise.
6. Prokaryotic and Eukaryotic Cells
Cells are grouped as prokaryotic or eukaryotic based on whether they have a true nucleus and membrane-bound organelles.
| Feature | Prokaryotic Cell | Eukaryotic Cell |
|---|---|---|
| True nucleus | Absent | Present |
| DNA | Free in cytoplasm, often circular | Inside nucleus |
| Membrane-bound organelles | Absent | Present |
| Size | Usually smaller | Usually larger |
| Example | Bacteria | Plant and animal cells |
Student Common Mistake: Bacteria do have genetic material, but they do not have a true nucleus.
7. Microscopy
A light microscope uses visible light and lenses to magnify cells. An electron microscope uses electrons and has much higher magnification and resolution.
| Microscope Part | Function |
|---|---|
| Eyepiece lens | Magnifies the image. |
| Objective lens | Provides different magnifications. |
| Stage | Supports the slide. |
| Light source / mirror | Illuminates the specimen. |
| Coarse adjustment | Rough focusing, usually on low power. |
| Fine adjustment | Sharpens the image. |
Using a Light Microscope
- Place the slide on the stage.
- Start with the lowest power objective lens.
- Use coarse adjustment to find the specimen.
- Use fine adjustment to sharpen the image.
- Increase magnification if needed.
Examiner Tip: Always start with low power because it gives a wider field of view.
8. Staining Cells
Many cells are nearly transparent, so stains are used to make structures easier to see.
| Stain | Common use | Purpose |
|---|---|---|
| Iodine | Onion/plant cells | Improves contrast and makes structures easier to see. |
| Methylene blue | Cheek/animal cells | Stains the nucleus and improves contrast. |
Examiner Trap: Stains do not magnify cells. They improve contrast.
9. Light Microscope vs Electron Microscope
| Feature | Light Microscope | Electron Microscope |
|---|---|---|
| Uses | Visible light | Electrons |
| Magnification | Lower | Much higher |
| Resolution | Lower | Higher |
| Specimens | Can sometimes view living cells | Specimens usually dead/prepared |
| Detail visible | Basic cell structures | Ultrastructure and very small organelles |
10. Common Student Mistakes
- Confusing cell wall and cell membrane.
- Writing that animal cells have cell walls.
- Forgetting mitochondria are the site of aerobic respiration.
- Forgetting chloroplasts are the site of photosynthesis.
- Saying bacteria have no DNA.
- Starting microscope work on high power.
- Thinking stains magnify cells.
- Forgetting electron microscopes have higher resolution.
11. Examiner Traps
Trap 1: A cell membrane controls movement in and out. A cell wall supports and strengthens.
Trap 2: Bacteria are prokaryotic, not eukaryotic.
Trap 3: Plant cells have mitochondria as well as chloroplasts.
Trap 4: Ribosomes are involved in protein synthesis.
Trap 5: Electron microscopes give greater detail because of higher resolution.
12. Examiner Secrets
Secret 1: For any organelle, learn name + function as a pair.
Secret 2: In plant vs animal comparisons, use a table.
Secret 3: In microscopy questions, mention low power first and fine adjustment for sharp focus.
Secret 4: For prokaryotes, say “no true nucleus” rather than “no DNA”.
13. Section A: Multiple Choice Practice
- Which structure controls movement of substances in and out of the cell?
A. Cell wall B. Cell membrane C. Vacuole D. Ribosome - Which organelle is the site of aerobic respiration?
A. Chloroplast B. Nucleus C. Mitochondrion D. Cell wall - Which structure is found in plant cells but not animal cells?
A. Cell membrane B. Nucleus C. Cell wall D. Cytoplasm - Which type of cell has no true nucleus?
A. Eukaryotic B. Prokaryotic C. Plant only D. Animal only - Why are stains used in microscopy?
A. To kill the cell only B. To improve contrast C. To reduce magnification D. To remove the nucleus
14. Section B: Structured Practice Questions
- State the function of the cell membrane, nucleus and mitochondria. [6 marks]
- Give three differences between plant and animal cells. [6 marks]
- Compare prokaryotic and eukaryotic cells. [4 marks]
- Describe how to use a light microscope to view a prepared slide. [5 marks]
- Explain why stains are used when viewing cells. [2 marks]
- Compare a light microscope and an electron microscope. [4 marks]
15. Mark Scheme Answers
Section A:
1. B 2. C 3. C 4. B 5. B
Q1. Cell membrane controls movement in/out [2]; nucleus controls activities/contains genetic material [2]; mitochondria site of aerobic respiration/energy release [2].
Q2. Plant cells have cell wall/chloroplasts/large vacuole/regular shape [any 3]; animal cells lack these or differ [matching comparison, 6].
Q3. Prokaryotes have no true nucleus/DNA free in cytoplasm/no membrane-bound organelles/smaller [any 2]; eukaryotes have nucleus/DNA in nucleus/membrane-bound organelles/larger [any 2].
Q4. Place slide on stage [1]; start low power [1]; use coarse focus [1]; use fine focus [1]; increase magnification if needed [1].
Q5. Stains improve contrast [1] and make structures such as nucleus easier to see [1].
Q6. Light microscope uses light/lower magnification/lower resolution/can sometimes view living cells [any 2]; electron microscope uses electrons/higher magnification/higher resolution/more detail [any 2].
1. B 2. C 3. C 4. B 5. B
Q1. Cell membrane controls movement in/out [2]; nucleus controls activities/contains genetic material [2]; mitochondria site of aerobic respiration/energy release [2].
Q2. Plant cells have cell wall/chloroplasts/large vacuole/regular shape [any 3]; animal cells lack these or differ [matching comparison, 6].
Q3. Prokaryotes have no true nucleus/DNA free in cytoplasm/no membrane-bound organelles/smaller [any 2]; eukaryotes have nucleus/DNA in nucleus/membrane-bound organelles/larger [any 2].
Q4. Place slide on stage [1]; start low power [1]; use coarse focus [1]; use fine focus [1]; increase magnification if needed [1].
Q5. Stains improve contrast [1] and make structures such as nucleus easier to see [1].
Q6. Light microscope uses light/lower magnification/lower resolution/can sometimes view living cells [any 2]; electron microscope uses electrons/higher magnification/higher resolution/more detail [any 2].
16. Quick Revision Card
- Cell membrane: Controls movement in and out.
- Cell wall: Supports and strengthens.
- Nucleus: Controls cell activities and contains DNA.
- Cytoplasm: Site of many reactions.
- Mitochondria: Aerobic respiration.
- Chloroplast: Photosynthesis.
- Ribosome: Protein synthesis.
- Prokaryote: No true nucleus.
- Stains: Improve contrast.
- Electron microscope: Higher magnification and resolution.
17. Interactive Simulator: Cell Structure Detective
Identify the Cell Structure
Clue: This structure controls movement of substances in and out of the cell.
Examiner Feedback
Ready
Choose the cell structure that matches the clue.
Score: 0/0
18. Mastery Checklist
- I can identify plant and animal cell structures.
- I can state the function of each organelle.
- I can compare plant and animal cells.
- I can compare prokaryotic and eukaryotic cells.
- I can describe how to use a light microscope.
- I can explain why stains are used.
- I can compare light and electron microscopes.
- I can answer OL exam questions on cells and microscopy.