GCSE Biology · AQA 8461 · Topic 4.1.1
Cell structure
Key points
- Animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. Plant cells also have a cellulose cell wall, chloroplasts and a permanent vacuole of cell sap.
- Bacteria are prokaryotic: no nucleus, a single loop of DNA in the cytoplasm and often small rings of DNA called plasmids. They are much smaller than eukaryotic cells.
- Specialised cells: sperm cells (tail, many mitochondria), nerve cells (long, branched ends), muscle cells (can contract), root hair cells (large surface area), xylem and phloem (transport).
- Differentiation is when a cell becomes specialised. Most animal cells differentiate early; many plant cells can differentiate throughout life.
- Electron microscopes have much higher magnification and resolution (the ability to tell two close points apart) than light microscopes.
- Magnification = image size ÷ real size. Remember 1 mm = 1000 µm; use standard form for very small sizes.
- Bacteria can be grown on agar plates using aseptic technique; gives the size of a clear zone around an antibiotic disc.
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Cells are the building blocks of all living things, but they come in two very different designs. Knowing the parts of each cell type, what they do and how scientists see them is the starting point for almost every other topic.
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