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Learn4BI1Paper 2B · Paper 2 (all content)Structure and functions in living organismsSpecialised cells and magnification
Structure and functions in living organisms · Subtopic 15 of 21

Specialised Cells and Magnification

Cells specialise to do particular jobs: root hair cells have a long extension for absorbing water; red blood cells have no nucleus and a biconcave shape to carry oxygen; sperm cells have a tail and many mitochondria. Similar cells form tissues, tissues form organs, organs form organ systems. Magnification =image sizeactual size=\frac{\text{image size}}{\text{actual size}}, using the same units; 1 mm=1000 μm1\ \text{mm}=1000\ \mu\text{m}.

Cambridge 5090 Paper 1Cambridge 5090 Paper 2Cambridge 0610 Papers 2, 4Cambridge 0610 Papers 1, 3Edexcel 4BI1 Paper 1BEdexcel 4BI1 Paper 2B≈ 40 minRevision 1 · updated 2026-10-30
Section 1 of 14

Learning objectives

  • Relate the structure of specialised cells to their function.
  • Describe levels of organisation.
  • Calculate magnification, image size and actual size, converting units.
Pause and think

Why doesn't your body just use one all-purpose type of cell?

Section 2 of 14

Core idea

Start hereShaped for the job

A sperm cell swims; a nerve cell stretches a metre; a red blood cell squeezes through capillaries narrower than itself. Every specialised cell's shape tells you what it does.

The big idea

Specialised cells have structures that suit their function. Cells group into tissues, organs and systems. Magnification = image ÷ actual size.

1. Specialised cells

  • Red blood cell: biconcave, no nucleus, haemoglobin.
  • Root hair: long extension, large surface area.
  • Palisade: many chloroplasts.
  • Neurone: long axon.
  • Ciliated: cilia sweep mucus.
  • Sperm: tail, mitochondria; egg: food store.

2. Magnification

M=IAM=\frac{I}{A}
where
M
magnification
I
image size
A
actual size (same units as I)
Worked exampleActual size of a chloroplast

A chloroplast in a photo is 12 mm long; magnification ×2400.

Goal
Actual length in μm.
Strategy
A=I/MA=I/M, then convert.
  1. A=122400=0.005 mmA=\frac{12}{2400}=0.005\ \text{mm}
    Divide image by magnification.
  2. 0.005×1000=5 μm0.005\times1000=5\ \mu\text{m}
    mm to μm: × 1000.
Answer5 μm5\ \mu\text{m}
✓ CheckChloroplasts are typically 2–10 μm ✓.
Levels of organisation

From smallest to largest.

Common misconceptionUnits Image and actual size must be in the same unit before dividing. Measure the drawing in mm and convert at the end.
Pause and think

Why can't you see ribosomes with a school light microscope?

Summary

  • Structure fits function.
  • Cell → tissue → organ → system.
  • M=I/AM=I/A; 1 mm = 1000 μm.
Key words
Tissue
Group of similar cells with a shared function.
Organ
Structure made of several tissues working together.
Magnification
How many times bigger the image is than the real object.
HistoryVan Leeuwenhoek. In the 1670s Antonie van Leeuwenhoek, a Dutch cloth merchant, ground his own tiny lenses and was the first to see bacteria and sperm cells, which he called "animalcules".
Fun factLongest cell. A single motor neurone running from the base of your spine to your big toe can be about a metre long.
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