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AQA GCSE Biology

Cell structure and organelles — AQA GCSE Biology revision

Free revision notes, key terms, common exam traps and 5 practice questions with answers. About 5 minutes to read.

Two cell types

  • Prokaryotic cells (bacteria) are tiny, have no nucleus, and keep their DNA as a single loop plus small rings called plasmids.
  • Eukaryotic cells (plants, animals, fungi) keep DNA inside a nucleus and have membrane-bound organelles.

What each part does

  • Nucleus: stores genetic instructions and controls the cell.
  • Mitochondria: site of aerobic respiration — energy transfer. Busy cells (muscle) have loads.
  • Ribosomes: build proteins.
  • Chloroplasts (plants only): contain chlorophyll for photosynthesis.
  • Permanent vacuole (plants): stores cell sap and keeps the cell firm.

Key terms

Organelle
A structure inside a cell with a specific job.
Plasmid
A small ring of extra DNA found in bacteria.
Differentiation
When a cell changes to become specialised for a job.
Magnification
How many times bigger the image is than the real object.
Eukaryote
An organism made of cells with a nucleus and membrane-bound organelles.
Prokaryote
An organism made of a single simple cell with no nucleus, e.g. bacteria.

Common exam traps

  • Saying plant cells have no mitochondria — they do; they respire too.
  • Mixing up cell wall (plants, made of cellulose) with cell membrane (all cells).
  • Forgetting units when converting mm → µm (×1000).

Practice questions with answers

  1. 1. Which structure is found in a prokaryotic cell but NOT in an animal cell?

    • • Ribosome
    • • Plasmid
    • • Cell membrane
    • • Cytoplasm

    Answer: Plasmid

    Plasmids are small DNA rings unique to bacteria among these options.

  2. 2. A muscle cell contains many mitochondria. Why?

    • • To store extra genetic material
    • • To release energy through aerobic respiration
    • • To make the cell rigid
    • • To absorb more water

    Answer: To release energy through aerobic respiration

    Contraction needs a lot of energy transfer, so more mitochondria.

  3. 3. State one adaptation of a root hair cell and explain how it helps.

    Answer: A long, thin projection gives a large surface area, so more water and minerals are absorbed.

    Always link the adaptation to the function for the mark.

  4. 4. An image is 50 mm wide and the real object is 100 µm. What is the magnification?

    Answer: ×500

    50 mm = 50 000 µm; 50 000 ÷ 100 = 500.

  5. 5. Which organelle controls the activities of a eukaryotic cell?

    • • Vacuole
    • • Nucleus
    • • Ribosome
    • • Cell wall

    Answer: Nucleus

    It contains the DNA that codes for proteins that run the cell.

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