Cell structure is the foundation of the National 5 Biology course—and a frequent source of quick-win marks. In this guide, we’ll break down the key organelles, what they do, and how to spot the exam traps. If you’d like 1-to-1 help, our SQA-experienced biology tutors at Central Tutors can build a study plan around your next prelim or the final exam.
What counts as a “cell” at National 5?
At this level, you compare animal, plant, fungal and bacterial cells and relate structure to function. You should be able to label diagrams, identify organelles in micrographs, and match each part to its job. (Find more information on Cell Structure from SQA here).
Key organelles and structures (with roles)
- Cell membrane – selectively permeable barrier controlling entry/exit of substances.
- Cytoplasm – site of many enzyme-controlled reactions.
- Nucleus (animals/plants/fungi) – contains genetic material; controls cell activities.
- Mitochondria – site of aerobic respiration; releases energy for cellular processes.
- Ribosomes – site of protein synthesis.
- Cell wall – provides shape/support; in plants (cellulose), fungi (chitin), and bacteria (peptidoglycan).
- Chloroplasts (plants, some algae) – photosynthesis (chlorophyll absorbs light).
- Vacuole (plant cells) – fluid-filled; maintains turgor pressure.
- Plasmids (bacteria) – small circular DNA; can carry useful genes.
This aligns with SQA’s organelle list and functions for Nat 5. BBC bitesize has a great page with more information on this, you can view it here.
Compare at a Glance: Animal, Plant, Fungal & Bacterial Cells
When revising for National 5 Biology, exam questions often ask you to spot similarities and differences between cell types. Here’s a clear comparison:
| Feature / Organelle | Animal Cell | Plant Cell | Fungal Cell | Bacterial Cell |
|---|---|---|---|---|
| Cell membrane | ✅ Present | ✅ Present | ✅ Present | ✅ Present |
| Cell wall | ❌ Absent | ✅ Cellulose | ✅ Chitin | ✅ Peptidoglycan |
| Nucleus | ✅ Present | ✅ Present | ✅ Present | ❌ Absent (DNA free in cytoplasm) |
| Cytoplasm | ✅ | ✅ | ✅ | ✅ |
| Mitochondria | ✅ | ✅ | ✅ | ❌ (respiration in cytoplasm) |
| Ribosomes | ✅ | ✅ | ✅ | ✅ |
| Chloroplasts | ❌ | ✅ (in green plants only) | ❌ | ❌ |
| Large Vacuole | ❌ | ✅ Central vacuole | ❌ (may have small ones) | ❌ |
| Plasmids | ❌ | ❌ | ❌ | ✅ (extra DNA rings) |
Key differences in cells explained
- Cell walls differ:
- Plants → cellulose
- Fungi → chitin
- Bacteria → peptidoglycan
- Animals → none
- Nucleus vs no nucleus:
- Animal, plant, fungal = eukaryotic (have nucleus)
- Bacteria = prokaryotic (DNA loose in cytoplasm + plasmids)
- Energy & food production:
- Plants → photosynthesis in chloroplasts
- Animals/fungi → no chloroplasts; rely on consuming/absorbing food
- Bacteria → no mitochondria; respiration in cytoplasm
- Storage:
- Plant cells → large central vacuole for water/sugars
- Animal cells → small vacuoles (if any)
- Fungal cells → small vacuoles; no chloroplasts
How cells are viewed and measured (exam-ready)
Using a Light Microscope
In National 5 Biology, you need to know how to prepare and use a light microscope. Key parts to remember are the eyepiece lens, objective lenses, stage, and focusing knobs. Stains such as iodine or methylene blue are often added to make structures easier to see. You may be asked to label a diagram of a microscope or describe how to focus on a specimen in an exam.
Measuring and Magnification
Cells and organelles are very small, so you’ll need to calculate their actual size using magnification. The formula is:
Magnification = Image size ÷ Actual size
Be careful with units — 1 mm = 1000 μm, and 1 μm = 1000 nm. Converting between these is a common exam hurdle, so always show your working.
Drawing Biological Diagrams
When asked to draw what you see under a microscope, examiners want clear, simple outlines — no shading or sketchy lines. Use a sharp pencil, label structures with straight lines, and include a scale bar if given. Marks are awarded for neatness, accuracy, and correct labelling, so practice drawing cells as part of your revision.
Typical exam questions (and how to answer)
Label the diagram (e.g., plant cell): memorise positions of wall, membrane, chloroplast, vacuole, nucleus, cytoplasm, mitochondria.
Match organelle → function: ribosome → protein synthesis; mitochondrion → aerobic respiration; vacuole → turgor.
Compare cells: one similarity + one difference (e.g., both have membranes; only plants have chloroplasts).
Bacteria focus: identify plasmids, absence of nucleus, cell wall composition difference
FAQs: National 5 Biology – Cell Structure
Q: What are the main differences between animal and plant cells at National 5?
A: Both have a cell membrane, cytoplasm, nucleus, mitochondria, and ribosomes. Plant cells also have a cell wall, chloroplasts for photosynthesis, and a large central vacuole.
Q: Do bacteria have a nucleus?
A: No. Bacterial cells are prokaryotic, which means they don’t have a nucleus. Instead, their DNA is free in the cytoplasm, often with extra rings of DNA called plasmids.
Q: What does the mitochondrion do?
A: Mitochondria are the site of aerobic respiration. They release energy in a form that the cell can use for processes such as growth, repair, and movement.
Q: How can I remember the functions of cell organelles for my exam?
A: Flashcards, quick quizzes, and simple mnemonics help. For example, “Mighty Mitochondria Make Energy” can remind you of their role in respiration.
Q: What type of microscope do you need to study cells in National 5 Biology?
A: You’ll be expected to know about the light microscope. It allows you to view basic cell structures like the nucleus, cytoplasm, and cell wall, but not smaller organelles like ribosomes.
Q: How do I calculate magnification in an exam question?
A: Use the formula Magnification = Image size ÷ Actual size. Always check your units — converting between millimetres (mm) and micrometres (µm) is a common place to slip up.
Q: Why do fungal cells not have chloroplasts?
A: Fungi don’t photosynthesise. Instead, they absorb nutrients from their surroundings, so they don’t need chloroplasts.
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