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2.5.3Inquiry Process

Specialised Cells — IB Biology HL Revision Notes & Topical Questions

5 min read 6 parts Lesson 61 of 160

📚 IB Biology HL Hub / Topical Revision
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Part 1 of 6Animal Cells

2.5.3 Specialised Cells

Differentiated cells have structures that suit their jobs.

Red blood cell
  • Biconcave shape with no nucleus gives a high surface area and room for haemoglobin to carry oxygen.
Neurone
  • Long axon carries impulses over distance, and branched dendrites receive signals from many cells.
Sperm cell
  • Flagellum for swimming, many mitochondria for energy and an acrosome with enzymes to penetrate the egg.
Egg cell
  • Large size with a store of food and cortical granules that help block entry of more than one sperm.
CellFeatureFunction
Red blood cellNo nucleus, biconcaveCarry oxygen
NeuroneLong axonTransmit impulses
SpermFlagellum, acrosomeReach and penetrate egg
Ciliated cellCiliaMove mucus

Part 2 of 6Plant Cells

Plant Cells
Palisade cell
  • Contains many chloroplasts and is tall and tightly packed to absorb light for photosynthesis.
Root hair cell
  • A long extension increases surface area for absorbing water and mineral ions.
Xylem vessel
  • Dead cells with lignified walls and no end walls form hollow tubes for water transport.
Guard cell
  • Pairs of cells that change shape to open and close stomata and control gas exchange.

Part 3 of 6Connecting Structure and Function

1
Identify what job the cell has to perform.
2
Look at which organelles are abundant, such as mitochondria for energy-demanding cells.
3
Note shape features such as extensions and folds that raise the surface area.
4
Link each feature to a specific advantage.
5
Check that the explanation uses the structure and the function.

Part 4 of 6Surface Area and Efficiency

Larger surface
  • Microvilli and root hairs increase the surface through which substances are absorbed.
Short diffusion distance
  • Thin cells such as alveolar cells allow fast gas exchange.
More organelles
  • Cells with high energy needs have large numbers of mitochondria.
Missing organelles
  • Red blood cells lose the nucleus to make room for haemoglobin.

Part 5 of 6Worked Example

Question

  • A scanning micrograph shows a red blood cell as 56 mm across at a magnification of ×8000.
  • Calculate its real diameter in micrometres.

  1. Actual size = image size ÷ magnification.
  2. 56 mm ÷ 8000 = 0.007 mm.
  3. 1 mm = 1000 µm, so 0.007 mm = 7 µm.

Answer The red blood cell has a diameter of 7 µm.

Part 6 of 6Exam Checklist & Tips

2.5.3 – Key Points for the Exam

  • Specialised cell A cell with a structure that suits a particular function.
  • Differentiation The process by which a cell becomes specialised.
  • Acrosome A vesicle at the sperm tip containing digestive enzymes.
  • Biconcave Shaped like a disc with a dip in the centre on both sides.

Common Mistakes

  • Giving a function without linking it to structure.
  • Saying specialised cells have different DNA.
  • Stating that red blood cells have mitochondria.
  • Describing xylem vessels as living cells.

Last updated:

Cambridge 9700 AS Biology Core Formula

Magnification Triangle & Unit Conversion

Formula: M = I / A  ⇔  A = I / M  ⇔  I = M × A

Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.