GCSE · Biology · AQA · Spec 8461

Eukaryotes and prokaryotes

Animal and plant cells are eukaryotic; bacterial cells are prokaryotic — and the key difference is whether DNA is enclosed in a nucleus.

What you need to know

  • Animal and plant cells are eukaryotic: they have a cell membrane, cytoplasm, and genetic material enclosed in a nucleus.
  • Bacterial cells are prokaryotic: much smaller than eukaryotic cells, with cytoplasm and a cell membrane surrounded by a cell wall.
  • Prokaryotic cells have no nucleus — the genetic material is a single loop of DNA free in the cytoplasm, and there may also be one or more small rings of DNA called plasmids.
  • Cell sizes span many orders of magnitude; use standard form and prefixes (centi, milli, micro, nano) to compare them.

The big picture

Animal and plant cells are eukaryotic: their genetic material is enclosed inside a nucleus. Bacterial cells are prokaryotic: they are much smaller than eukaryotic cells and have no nucleus. Their genetic material is a single DNA loop free in the cytoplasm, and they may also contain one or more small rings of DNA called plasmids. Cell sizes can be compared using standard form and the prefixes centi, milli, micro and nano.

TONIGHT'S REVISION

Eukaryotes and prokaryotes

The nucleus makes all the difference — here is how animal, plant and bacterial cells compare.

Building both cell types — stage by stage

Follow each stage to build a clear picture of eukaryotic and prokaryotic cells.

Stop and predict

Commit to your answer before revealing — this is where your understanding is tested.

A cell description reads: 'cell membrane present, cytoplasm present, cell wall present, genetic material is a single loop of DNA'. Does this cell have a nucleus?

Why does the nucleus matter so much?

?

Reason it through

Why does the presence or absence of a nucleus define the two categories of cell?

Link 1 of 3

First link · your turn

What does having a nucleus mean for how the genetic material is stored in a eukaryotic cell?

2
Locked — reveal the link above first
3
Locked — reveal the link above first

Relationship matrix

Tap any cell to reveal it. Tap a column header to read one property down every item.

Nucleus present?Form of genetic materialPlasmids stated?Cell wall present?
Eukaryotic celle.g. animal or plant cell
Prokaryotic celle.g. bacterium

Each cell hides a short answer and the reason behind it. Predict before you tap.

Exam-style practice

Practice: describe the differences — 3 marks.

Check your answer covers each marking point.

Question

Describe the differences between a eukaryotic cell and a prokaryotic cell. [3 marks]

Student answer

Eukaryotic cells have a nucleus that contains the genetic material, whereas prokaryotic cells have no nucleus. In prokaryotic cells the genetic material is a single loop of DNA free in the cytoplasm. Prokaryotic cells are much smaller than eukaryotic cells.

Method marks0/3

Key points

1Eukaryotic = nucleus present; prokaryotic = no nucleus — this is the defining difference.
2Bacteria are prokaryotic: their DNA is a single loop free in the cytoplasm, not enclosed in a nucleus.
3Plasmids are small rings of DNA that may be present in prokaryotic cells.
4Prokaryotic cells are much smaller than eukaryotic cells.
5Plant and animal cells share a cell membrane, cytoplasm, and a nucleus; bacterial cells have a cell wall outside the cell membrane.

Worked example

Problem

A student is given two cells to compare. Cell A is 10 µm across and has its DNA enclosed in a nucleus. Cell B is 2 µm across, has no nucleus, and has a cell wall surrounding its cell membrane. Identify each cell type and justify your answer.

🧠

Memory hook

Plant and animal cells: genetic material inside a nucleus. Bacterial cells: no nucleus — a single DNA loop is free in the cytoplasm.

⚠ Watch out

Students write that bacteria have 'no DNA' — this is wrong. Bacteria do have DNA; it is simply not enclosed in a nucleus. It exists as a single loop free in the cytoplasm.

✓

Check yourself

Without looking — name three structural features of a bacterial cell, and state the one key feature it does NOT have that animal and plant cells do.

Flashcards

(24)
What does 'eukaryotic' mean?
A cell type that has its genetic material enclosed in a nucleus. Animal and plant cells are eukaryotic.
What does 'prokaryotic' mean?
A cell type with no nucleus. The genetic material is a single loop of DNA free in the cytoplasm. Bacteria are prokaryotic.
Name three features shared by plant and animal cells.
Cell membrane, cytoplasm, and genetic material enclosed in a nucleus.
Name three structural features a bacterial (prokaryotic) cell has.
Cell membrane, cytoplasm, and a cell wall surrounding the cell membrane.
What is a plasmid?
A small ring of DNA that may be present in prokaryotic cells, separate from the main DNA loop.
How many plasmids can a prokaryotic cell have?
One or more — the specification states there 'may be one or more small rings of DNA called plasmids'.
How does the size of a prokaryotic cell compare to a eukaryotic cell?
Prokaryotic cells are much smaller than eukaryotic cells.
Where is the genetic material in a prokaryotic cell?
Free in the cytoplasm as a single loop of DNA — not enclosed in a nucleus.
Where is the genetic material in a eukaryotic cell?
Inside the nucleus.
What is the shape of bacterial DNA?
A single loop (circular shape) of DNA.
What type of cell is a bacterium?
Prokaryotic.
What type of cells are animal and plant cells?
Eukaryotic.
What is the single most important structural difference between eukaryotic and prokaryotic cells?
Eukaryotic cells have a nucleus enclosing their genetic material; prokaryotic cells have no nucleus — the DNA is free in the cytoplasm.
Do bacterial cells have a cell wall?
Yes — bacterial cells have a cell wall surrounding their cell membrane.
What prefix means one millionth (10⁻⁶)?
Micro (µ) — as in micrometre (µm).
What prefix means one thousandth (10⁻³)?
Milli (m) — as in millimetre (mm).
What prefix means one billionth (10⁻⁹)?
Nano (n) — as in nanometre (nm).
What prefix means one hundredth (10⁻²)?
Centi (c) — as in centimetre (cm).
A cell is 0.000002 m across. Write this in standard form.
2 × 10⁻⁶ m (2 µm).
A bacterium is 3 µm long. Express this in metres in standard form.
3 × 10⁻⁶ m.
Why is it wrong to say bacteria have no DNA?
Bacteria do have DNA — a single loop free in the cytoplasm. They have no nucleus, but they do have genetic material.
Name one thing that is the same in both prokaryotic and eukaryotic cells.
Both have a cell membrane and cytoplasm.
What structural feature does a bacterial cell have outside its cell membrane that an animal cell does not?
A cell wall.
How can you identify a prokaryotic cell from a written description?
No nucleus is mentioned; DNA is described as a loop free in the cytoplasm; the cell is much smaller than a eukaryotic cell; a cell wall is present.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

Learn Eukaryotes and prokaryotes properly — interactive practice, marked questions and flashcards.

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