Cells and organisation · GCSE Biology
Eukaryotic and prokaryotic cells
Compare eukaryotic and prokaryotic cells for GCSE Biology: nucleus versus a DNA loop, plasmids, organelles, and the diagram tests that decide Combined and Triple marks.
Nucleus present: eukaryotic (animal, plant, fungus). No nucleus, DNA as a loop in the cytoplasm: prokaryotic (bacterium). Then hunt for plasmids, flagella and a cellulose wall.
The important bits
What you need to know
- 1
Eukaryotic cells store DNA as chromosomes inside a nucleus. Animal, plant and fungal cells are eukaryotic. Typical animal cell diameter is about 10–30 µm; plant cells are often larger.
- 2
Prokaryotic cells have no nucleus. Chromosomal DNA is a single circular loop in the cytoplasm. Many bacteria also carry plasmids: extra small rings of DNA that can carry genes such as antibiotic resistance.
- 3
Both cell types have a cell membrane (controls entry and exit), cytoplasm (site of most chemical reactions) and ribosomes (protein synthesis). Ribosomes in prokaryotes are smaller (70S) than in eukaryotes (80S) — Triple may mention size, Combined needs the function.
- 4
Mitochondria are eukaryotic organelles: the site of aerobic respiration. Prokaryotic cells have no mitochondria; they respire using enzymes in the cytoplasm and cell membrane.
- 5
Chloroplasts are eukaryotic plant organelles containing chlorophyll. Bacteria that photosynthesise do not have chloroplasts; some have chlorophyll in the cytoplasm instead.
- 6
A cellulose cell wall is a plant eukaryotic feature. Bacterial cell walls are not cellulose (often peptidoglycan). Do not write “all cells have a cell wall”.
- 7
Flagella (singular: flagellum) rotate or whip to move some bacterial cells. Some eukaryotic cells (sperm) also have a flagellum, so the presence of a flagellum alone does not prove the cell is prokaryotic.
- 8
Scale: bacteria are typically 1–5 µm, so a light microscope can show the outline but not plasmids. Electron microscopes resolve the DNA loop, ribosomes and flagella in detail.
Quotations worth analysing
Short evidence. Real method.
“Eukaryotic cells have a nucleus; prokaryotic cells do not.”
This is the first sorting rule. Name the nucleus (or its absence) before listing extra structures, or you lose the classification mark.
“Bacterial DNA is a single loop, not chromosomes inside a nucleus.”
Examiners reject “the bacterium’s nucleus”. Call it chromosomal DNA or a loop of DNA in the cytoplasm, plus plasmids if shown.
“Mitochondria are the site of aerobic respiration.”
Use this phrase, then add that prokaryotes lack mitochondria. “Where energy is made” is too vague and scores poorly.
Go deeper
How do I tell the cell type from a blank diagram?
Start with the nucleus test, not a memorised list. A clearly drawn nucleus with a nuclear membrane means eukaryotic: then decide animal versus plant. Plant extras are a cellulose cell wall, chloroplasts and a large permanent vacuole of cell sap. No nucleus and a coiled loop of DNA means prokaryotic. Next look for plasmids and a flagellum. Mitochondria appear only in eukaryotes that respire aerobically; never add them to a bacterium. Ribosomes sit in both, but school light microscopes cannot resolve them, so an exam diagram that shows dots labelled ribosomes is usually an electron micrograph. Write the type first, then one function for each labelled part. “It is a cell” earns nothing; “prokaryotic because DNA is a loop in the cytoplasm” earns the mark.
Go deeper
Why do bacteria still respire if they have no mitochondria?
Respiration is a chemical process, not a building. Enzymes in the cytoplasm (and in the bacterial cell membrane) transfer energy from glucose. Mitochondria simply package those reactions in eukaryotes and transfer much more energy when oxygen is available. That is why a root hair cell is packed with mitochondria for active transport, but a bacterium can still take up ions using membrane proteins and energy from respiration. In the exam, “no mitochondria so bacteria cannot respire” is a classic wrong line. Write: prokaryotes respire in the cytoplasm; they just lack the organelle. If the question asks where aerobic respiration happens in a liver cell, the answer is mitochondria. If it asks in a bacterium, the answer is cytoplasm.
Go deeper
What extra structures actually matter on Triple papers?
Combined wants the nucleus test plus plasmids, flagella and the plant trio. Triple may add slime capsules (protect against drying and phagocytosis), pili, and the idea that bacterial ribosomes are smaller. Do not invent a nucleus “sort of in the middle”. Plasmids are the genetic-engineering hook: they can be cut with restriction enzymes and used to insert human insulin genes. Flagella explain motility in pond-water bacteria questions. A cellulose wall versus a bacterial wall is the plant-versus-bacterium discriminator when both cells are box-shaped. Keep fungal cells in the eukaryotic camp: they have a nucleus and a wall, but the wall is chitin, not cellulose. If the paper shows a yeast cell, treat it as eukaryotic and mention the nucleus.
See the idea in action
A diagram shows a cell 2 µm long with a cell wall, cell membrane, cytoplasm, a loop of DNA and two small rings of DNA. It has no nucleus and no mitochondria. Classification: prokaryotic (bacterial). The loop is chromosomal DNA; the rings are plasmids. Protein synthesis occurs at ribosomes in the cytoplasm. Aerobic respiration, if it occurs, uses enzymes in the cytoplasm and membrane, not mitochondria. An animal cell of 20 µm would show a nucleus and mitochondria and would lack the DNA loop and plasmids.
Exam technique
Turn knowledge into marks
On compare questions, use a running pair: “eukaryotes have a nucleus, prokaryotes have a DNA loop”. Then add one unique prokaryotic feature (plasmid or flagellum) and one unique eukaryotic organelle (mitochondrion or chloroplast). Never write that bacteria have a nucleus.
Common mistakes
Do not give these marks away
- 01
Calling the bacterial DNA loop a nucleus, or drawing mitochondria inside a prokaryotic cell.
- 02
Assuming any cell with a wall is a plant: bacterial and fungal cells also have walls, but not cellulose (plants).
- 03
Writing that prokaryotes cannot respire, or that plasmids are found in animal cells.
Which feature is found in a typical prokaryotic cell but not in an animal cell?
ANucleus
BMitochondria
CPlasmid DNA
DChloroplasts
Show the answer
Plasmid DNA. Bacteria store extra genes on plasmids. Animal cells are eukaryotic: they have a nucleus and mitochondria, but not plasmids or chloroplasts.
Quick questions
If this is the bit you searched
What is the difference between eukaryotic and prokaryotic cells GCSE?
Eukaryotic cells (animals, plants, fungi) have a nucleus. Prokaryotic cells (bacteria) have no nucleus; their chromosomal DNA is a loop in the cytoplasm, often with plasmids.
Do bacteria have mitochondria?
No. Mitochondria are eukaryotic organelles. Bacteria respire using enzymes in the cytoplasm and cell membrane.
What are plasmids in bacteria?
Small rings of DNA separate from the chromosomal loop. They may carry genes such as antibiotic resistance and are used in genetic engineering.
Are plant cells eukaryotic or prokaryotic?
Eukaryotic. They have a nucleus, mitochondria, a cellulose cell wall, chloroplasts and a permanent vacuole.