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GCSE Biology Cell Structure Notes (AQA 8461)
Eukaryotic and prokaryotic cells, animal and plant cells, specialised cells, differentiation, microscopy and culturing bacteria – in quick bullet points with memory tricks. Follows AQA GCSE Biology 4.1.1, including required practicals 1 and 2.
Try the calculatorsBook a 1-to-1 lessonWritten by Ms. Humaira Asim, a science teacher with 15+ years of teaching experience. Checked against the AQA GCSE Biology (8461) specification, section 4.1.1.
Eukaryotic cells (animal and plant) keep their DNA in a nucleus. Prokaryotic cells (bacteria) are much smaller, with no nucleus – just a DNA loop and plasmids. Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes; plant cells also have chloroplasts, a permanent vacuole and a cellulose cell wall.
- Only in AQA: eukaryotes vs prokaryotes, orders of magnitude and standard form, light vs electron microscopes (resolution), cell differentiation, required practical 1 (microscopy), culturing bacteria and required practical 2 Biology only.
- Different specialised cells: AQA = sperm, nerve, muscle, root hair, xylem, phloem. IGCSE = ciliated, root hair, palisade, neurone, red blood cell, sperm, egg.
- Only in IGCSE: levels of organisation (cell → tissue → organ → system) are in this topic. (AQA covers them in 4.2 Organisation.)
- Studying Cambridge IGCSE instead? See the IGCSE Cells notes.
What is the difference between eukaryotic and prokaryotic cells?
Prokaryotes have no nucleus. Eukaryotes have a true nucleus.
| Eukaryotic | Prokaryotic | |
|---|---|---|
| Examples | Animal, plant (and algal) cells | Bacteria |
| Genetic material | In a nucleus | Single DNA loop + plasmids, no nucleus |
| Size | Larger (about 10–100 µm) | Much smaller (about 1–10 µm) |
| Always has | Cell membrane, cytoplasm | Cell membrane, cytoplasm, cell wall |
Size, scale and units
- mm → µm → nm: ×1000 each step. Smaller unit = bigger number.
| Unit | In metres | Example |
|---|---|---|
| millimetre (mm) | 10−3 m | Ant’s head |
| micrometre (µm) | 10−6 m | Cells (bacteria ~1 µm) |
| nanometre (nm) | 10−9 m | Ribosomes (~20 nm) |
- Order of magnitude = how many powers of 10 bigger. A 100 µm plant cell is about 102 times bigger than a 1 µm bacterium (2 orders of magnitude).
- Use standard form for very big or small answers, e.g. 0.000 002 m = 2 × 10−6 m.
What are the parts of animal and plant cells?
- Animal cells: nucleus, cytoplasm, cell membrane, mitochondria, ribosomes.
- Plant and algal cells have a cellulose cell wall that strengthens the cell.
- Plant cells often (not always) have chloroplasts and a permanent vacuole.
- Be able to estimate the relative size of parts, e.g. the nucleus takes up about a tenth of an animal cell’s width.
What does each part do?
| Part | Job | Hook |
|---|---|---|
| Nucleus | Genetic material; controls the cell | Boss’s office |
| Cytoplasm | Chemical reactions happen here (enzymes) | Kitchen |
| Cell membrane | Controls what goes in and out | Bouncer |
| Mitochondria | Aerobic respiration | Power station |
| Ribosomes | Protein synthesis | Protein factory |
| Chloroplasts | Photosynthesis (contain chlorophyll) | Solar panels |
| Permanent vacuole | Contains cell sap | Water balloon |
| Cell wall (cellulose) | Strengthens the cell | Brick wall |
| DNA loop / plasmids | Bacterial genetic material | Loose loop |
What specialised cells do you need to know?
Sperm · Nerve · Muscle (animal) · Root hair · Xylem · Phloem (plant)
| Cell | Job | Adaptations |
|---|---|---|
| Sperm | Reach and fertilise the egg | Tail to swim; many mitochondria for energy; enzymes in the head to get into the egg |
| Nerve | Carry electrical impulses | Long, to cover distance; branched endings to connect to other cells |
| Muscle | Contract | Protein fibres that slide to contract; many mitochondria |
| Root hair | Absorb water and mineral ions | Hair-like extension = large surface area; many mitochondria for active transport |
| Xylem | Carry water and ions up the plant | Dead, hollow tubes with no end walls; lignin makes them strong |
| Phloem | Carry dissolved sugars | Sieve plates with pores; companion cells supply energy |
What is cell differentiation?
- Differentiation = a cell changes to become specialised, gaining the sub-cellular structures it needs for its job.
- Animals: most cells differentiate early. In adults, cell division is mainly for repair and replacement.
- Plants: many cells keep the ability to differentiate throughout life.
Light microscope vs electron microscope
- Resolution = the smallest distance between two points that can still be seen as separate. Higher resolution = sharper detail.
| Light microscope | Electron microscope | |
|---|---|---|
| Magnification | Up to about ×2000 | Up to about ×2 000 000 |
| Resolution | About 200 nm | About 0.2 nm (much higher) |
| Can see | Cells, nucleus, chloroplasts | Also ribosomes, inside mitochondria |
| Specimens | Living or dead, in colour | Dead only, black and white |
- Electron microscopes helped biologists see and understand many more sub-cellular structures.
How do you calculate magnification?
- magnification = size of image ÷ size of real object
- Put both sizes in the same unit first.
- Give very big or small answers in standard form.
Required practical 1: microscopy
- Put a drop of water on a slide; add a thin layer of onion epidermis.
- Add a drop of iodine to stain the cells.
- Lower a coverslip at an angle with a mounted needle (no air bubbles).
- Start with the lowest-power objective; focus with the coarse, then fine focus.
- Draw in pencil: clear lines, no shading, labelled, with a scale / magnification.
- Total magnification = eyepiece × objective (e.g. ×10 × ×40 = ×400).
Culturing microorganisms Biology only
- Bacteria divide by binary fission – as often as every 20 minutes with enough nutrients and a suitable temperature.
- Grow them in nutrient broth or as colonies on agar gel plates.
- Number of bacteria = start number × 2number of divisions Higher tier give the answer in standard form.
- Area of a clear zone = πr².
Aseptic technique
- Sterilise Petri dishes and agar before use.
- Flame the inoculating loop to kill microbes on it.
- Tape the lid on, but don’t seal it all round.
- Store the dish upside down.
- Incubate at 25 °C in school.
- Why 25 °C? Harmful pathogens that grow at body temperature (37 °C) are less likely to grow.
- Why upside down? Condensation drips away from the agar.
- Why not fully sealed? Oxygen can get in, so harmful anaerobic bacteria don’t grow.
Required practical 2: antiseptics or antibiotics Biology only
- Spread bacteria on an agar plate; add paper discs soaked in different antiseptics or antibiotics (plus a control disc in sterile water).
- Incubate at 25 °C, then measure the clear zone (zone of inhibition) around each disc.
- Bigger clear zone = more effective at killing or stopping bacteria.
Worked examples
Example 1: magnification with different units
An image of a bacterium is 5 mm long. The real bacterium is 2.5 µm long. Calculate the magnification.
- Same units: 5 mm = 5000 µm
- M = 5000 ÷ 2.5
- = ×2000
Example 2: real size in standard form
A mitochondrion is 20 mm long in an electron micrograph at ×10 000. Find its real size in metres.
- Real size = image ÷ magnification = 20 ÷ 10 000 = 0.002 mm
- 0.002 mm = 2 µm = 2 × 10−6 m
Example 3: bacterial growth (Biology only)
One bacterium divides every 20 minutes. How many are there after 2 hours?
- 2 hours = 120 min → 120 ÷ 20 = 6 divisions
- Number = 1 × 26
- = 64 bacteria
Example 4: clear zone area (Biology only)
A clear zone has a diameter of 16 mm. Calculate its area.
- r = 16 ÷ 2 = 8 mm
- Area = π × 8²
- ≈ 201 mm²
Calculators
Magnification (I AM)
The calculator converts the units for you.
Bacterial growth Biology only
number = start × 2divisions
Clear zone area Biology only
area = πr² (r = diameter ÷ 2)
Quick quiz
Quick quiz: cell structure (AQA)
Instant feedback on every answer.
1. Which type of cell has no nucleus?
2. Why can an electron microscope show ribosomes but a light microscope cannot?
3. Which cell is NOT on the AQA specialised cell list?
4. How many micrometres are in 1 millimetre?
5. Why are school bacterial cultures incubated at 25 °C or below?
6. A bacterium divides every 20 minutes. How many bacteria after 1 hour, starting from 1?
Common mistakes
- Mixing up magnification and resolution. Resolution is about detail, not size.
- Forgetting to convert units before using I AM.
- Saying all plant cells have chloroplasts. Root cells don’t.
- Saying bacteria have a nucleus. They have a DNA loop and plasmids.
- Incubating at 37 °C in school – it must be 25 °C.
Frequently asked questions
What is the difference between eukaryotic and prokaryotic cells?
Eukaryotic cells (plant and animal cells) have their genetic material inside a nucleus. Prokaryotic cells (bacteria) are much smaller and have no nucleus: their DNA is a single loop, and they may have small rings of DNA called plasmids.
What is required practical 1 in AQA GCSE Biology?
Required practical 1 is using a light microscope to observe, draw and label plant and animal cells, including a magnification scale.
Why does an electron microscope show more detail than a light microscope?
An electron microscope has a much higher magnification and resolution (resolving power), so it can show small sub-cellular structures such as ribosomes in much finer detail.
What specialised cells do I need to know for AQA GCSE Biology?
Animal cells: sperm cells, nerve cells and muscle cells. Plant cells: root hair cells, xylem cells and phloem cells.
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Book a 1-to-1 lessonFree worksheetsThese notes follow the AQA GCSE Biology (8461) specification, section 4.1.1. Always check the current specification on the AQA website. Also see: IGCSE Cells notes · Combined Science notes.