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GCSE Biology

Cell structure and microscopy

Compare animal, plant and bacterial cells, know what each part does, and calculate magnification and real size from microscope images.

  • Tier Combined Science and Separate Biology
  • Boards AQA, Edexcel, OCR, Eduqas, WJEC, CCEA
  • Time about 14 min
  • Unit Cells and organisation
NotesWorksheetQuiz

Notes

Key idea: all living things are made of cells. Eukaryotic cells (animals, plants, fungi, protists) have a nucleus. Prokaryotic cells (bacteria) do not.

Animal and plant cells

Animal and plant cells are both eukaryotic. These parts are found in both:

Part What it does
Nucleus Contains the genetic material (DNA) and controls the cell's activities
Cytoplasm A jelly-like liquid where most chemical reactions happen
Cell membrane Controls what moves into and out of the cell
Mitochondria Where aerobic respiration releases energy
Ribosomes Where proteins are made (protein synthesis)

Plant cells also have:

Part What it does
Cell wall Made of cellulose. Strengthens the cell and supports the plant
Permanent vacuole Filled with cell sap. Keeps the cell firm
Chloroplasts Contain chlorophyll. Where photosynthesis happens

Bacterial cells

Bacteria are prokaryotes. They are much smaller than animal and plant cells (typically a few micrometres across).

  • Cytoplasm, a cell membrane and a cell wall (not made of cellulose)
  • No nucleus. The genetic material is a single loop of DNA free in the cytoplasm
  • Often extra small rings of DNA called plasmids
  • Some have a flagellum (a tail-like structure) for movement

Specialised cells

Cells become specialised for a job. A few examples:

Cell Special feature Why it helps
Sperm cell Tail and many mitochondria Swims to the egg, using energy from respiration
Muscle cell Many mitochondria and protein fibres that shorten Releases energy for contraction
Nerve cell Long axon and branched ends Carries electrical impulses over long distances
Root hair cell Long, thin hair-like extension Large surface area for absorbing water and minerals

Microscopes

  • Light microscope: cheap and easy to use. Shows the nucleus, cytoplasm and sometimes chloroplasts and the cell wall.
  • Electron microscope: much higher magnification and resolution (the ability to see two close points as separate). Shows tiny structures such as ribosomes, plasmids and the inside of mitochondria.

Magnification

$$\text{magnification} = \frac{\text{size of image}}{\text{size of real object}}$$

Rearranged: real size = image size ÷ magnification, and image size = real size × magnification.

Always use the same units. Convert first:

  • 1 mm = 1000 µm (micrometres)
  • 1 µm = 1000 nm (nanometres)

Example 1: an image is 12 mm across and the real cell is 0.06 mm. The magnification is $12 \div 0.06 = 200$, so ×200.

Example 2: an image is 45 mm long and the magnification is ×300. The real length is $45 \div 300 = 0.15$ mm, which is $0.15 \times 1000 = 150$ µm.

Common mistakes

  • Mixing units in the magnification calculation. Convert to the same unit first.
  • Saying plant cells "have a cell wall and animal cells don't have a cell membrane". All cells have a membrane.
  • Writing that bacteria "have no DNA". They do. It isn't in a nucleus.
  • Muddling magnification and resolution: electron microscopes are better at both.

Worksheet

Websink Prep UK · GCSE Biology: Cell structure and microscopy

Name: ____________________   Date: ____________   Score: ______

  1. Match each part to its job: nucleus, mitochondria, ribosomes, chloroplasts, cell wall, cell membrane.
    • (a) Controls what enters and leaves the cell
    • (b) Where aerobic respiration takes place
    • (c) Where protein synthesis happens
    • (d) Contains the genetic material
    • (e) Where photosynthesis happens
    • (f) Made of cellulose and strengthens the cell
  2. Give two features found in plant cells but not in animal cells.
  3. Explain why a muscle cell has many mitochondria.
  4. Give two differences between a bacterial cell and an animal cell.
  5. An image of a cell is 12 mm long. The real cell is 0.06 mm long. Calculate the magnification.
  6. A student's drawing of a cell is 45 mm long. The microscope magnification was ×300. Calculate the real length of the cell. Give your answer in µm.
  7. Convert 0.02 mm to µm.
  8. A cell is 25 µm wide. How many of these cells would fit side by side across 1 mm?
  9. Explain why an electron microscope can show more detail of a cell than a light microscope.

Quick quiz

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