Myers Science HubCambridge IGCSE Co-ordinated Sciences 0654
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Biology B2–B3 · Core + Supplement

Cells: structure, scale and exchange

Explore cells, calculate real biological sizes and model how substances cross membranes. Each lesson ends with Cambridge-style questions and instant feedback.

Plant · animal · bacterialmm ↔ µmDiffusion · osmosis · active transport
Your route

Three connected lessons

  1. Cell structure: identify structures, connect structure to function, compare cells and recognise specialised cells.
  2. Cell size and magnification: convert units and rearrange the magnification equation accurately.
  3. Movement in and out: distinguish diffusion, osmosis and active transport and interpret practical data.
Exam focus: recall matters, but Cambridge also assesses application, numerical work, interpretation and experimental skills.

Syllabus alignment

This suite follows the current 2025–2027 Cambridge 0654 syllabus: B2.1 Cell structure, B2.2 Size of specimens, and B3.1–B3.3 Movement into and out of cells. “Core + Supplement” labels identify Extended detail.

Official syllabus link appears in the Sources section at the end of the suite.

Lesson 1 · B2.1

Cell structure and organisation

Success criteria: I can identify organelles from diagrams, state precise functions, compare three cell types, identify the required specialised cells, and explain how their structures are adapted to their functions.

Interactive cell explorer

Select a structure in the plant cell.

Select an organelle to reveal its function.

Watch: cell types and structures

Cognito, “Cell Types and Cell Structure”. If embedding is blocked by school filtering, open the video on YouTube.

Compare

StructureAnimalPlantBacterium
Cell membrane, cytoplasm, ribosomes✓✓✓
Nucleus✓✓—
Cell wall—CellulosePresent
Circular DNA / plasmids——✓
Chloroplasts, large vacuole—Often—
Required content · B2.1

Specialised cells: structure is linked to function

Core idea: specialised cells have structures that help them carry out particular functions. For each cell, learn the function first, then connect the structural adaptations to that function.

Watch: specialised cells

The specialised-cells section begins at about 4:40. It reviews ciliated cells, root hair cells, palisade mesophyll cells, red blood cells, neurones, sperm cells and egg cells. If embedding is blocked by school filtering, open the video on YouTube.

Animal cell

Ciliated cell

Cilia sweep mucus along

Function: moves mucus in the trachea and bronchi.

Adaptations: hair-like cilia beat in coordinated waves to move mucus containing trapped dust and microorganisms toward the throat.

Plant cell

Root hair cell

Long root hair

Function: absorption of water and mineral ions from the soil.

Adaptations: long hair-like extension gives a large surface area; thin wall gives a short pathway for water; many mitochondria provide energy for active transport of mineral ions.

Plant cell

Palisade mesophyll cell

Packed with chloroplasts

Function: photosynthesis.

Adaptations: many chloroplasts absorb light; cells are packed near the upper surface of the leaf; elongated shape allows many cells to fit where light intensity is high.

Animal cell

Neurone

Myelin sheath on axon

Function: conducts electrical impulses.

Adaptations: long axon carries impulses over long distances; branched ends connect with other cells; insulating myelin can increase the speed of transmission.

Animal cell

Red blood cell

Biconcave discNo nucleus → more space for haemoglobin

Function: transports oxygen.

Adaptations: contains haemoglobin to bind oxygen; biconcave shape provides a large surface area; no nucleus leaves more space for haemoglobin; flexible shape helps it pass through capillaries.

Gamete

Sperm cell

AcrosomeFlagellum for swimming

Function: male gamete for reproduction; delivers male genetic material to the egg.

Adaptations: flagellum enables movement; many mitochondria provide energy for swimming; acrosome contains enzymes that help penetrate the egg; haploid nucleus contains one set of chromosomes.

Gamete

Egg cell

Large nutrient-rich cytoplasm

Function: female gamete for reproduction; fuses with sperm during fertilisation.

Adaptations: large cytoplasm contains resources for early development; haploid nucleus contains one set of chromosomes; cell surface changes after fertilisation help prevent entry of additional sperm.

Exam technique: when asked how a cell is adapted to its function, write a structure → function link. Example: “A root hair cell has a long extension, which increases surface area, allowing faster absorption of water and mineral ions.”

Specialised-cell check

Which cell is correctly matched to its function?

Adaptation check

Why does a palisade mesophyll cell contain many chloroplasts?

Organisation sorter

Choose the correct sequence from smallest to largest.

Lesson 2 · B2.2

Cell size and magnification

Success criteria: I can convert mm and µm, select and rearrange the equation, include units and show clear working.

The essential relationship

magnification = image size ÷ actual size

Non-negotiable: image size and actual size must be in the same unit before division. 1 mm = 1000 µm.
01 mm2 mm3 mm4 mm

Watch: magnification calculations

Open on YouTube if the embedded player is restricted.

Magnification laboratory

Choose what to find and enter the other two values.

Convert sizes to the same unit before using the calculator.

Worked example

An electron micrograph shows a cell measuring 45 mm. Its actual diameter is 15 µm.

  1. Convert: 45 mm = 45 000 µm
  2. M = image ÷ actual
  3. M = 45 000 ÷ 15 = ×3000
Magnification has no unit; write it as ×3000. Do not write “3000 µm”.
Quick check: 0.075 mm equals…
Lesson 3 · B3.1–B3.3

Movement into and out of cells

Success criteria: I can compare diffusion, osmosis and active transport, predict cell changes, explain factors affecting rate and interpret an osmosis investigation.

Particle model: diffusion

Move the slider to model time. Particles spread because of random movement; the net movement is down the concentration gradient.

Faster diffusion: larger surface area, higher temperature, steeper concentration gradient, shorter diffusion distance.

Process comparison

Direction
DiffusionHigh → low
OsmosisHigher → lower water potential, through a partially permeable membrane
Active transportLow → high; energy from respiration

Plant-cell predictor

Pure water outside: water enters; vacuole expands; cell becomes turgid. The wall resists expansion and turgor pressure develops.
Concentrated solution outside: water leaves; cell becomes flaccid. If the membrane pulls away from the wall, the cell is plasmolysed.

A plant cell has lower water potential than the surrounding solution. What happens?

Watch: active transport

Open active transport video on YouTube.

IGCSE application: root hair cells take up mineral ions even when the soil has a lower ion concentration than the cell. This requires energy released by respiration.
Original Cambridge-style practice

Paper 2, Paper 4 and Paper 6 practice

Answer first, then reveal the indicative mark points. Structured responses are not auto-graded because valid scientific wording can vary.

Paper 2 · Multiple choice

1. Which structure contains circular DNA but is not surrounded by a nucleus?[1]
2. A cell image is 36 mm wide and the actual cell is 12 µm wide. What is the magnification?[1]
3. Which change increases diffusion rate?[1]

Paper 4 · Structured theory

4. Compare the structures of a plant cell and a bacterial cell.[4]
Any four: both have cell wall / membrane / cytoplasm / ribosomes; plant has nucleus but bacterium has circular DNA free in cytoplasm; bacterium may have plasmids; plant may have chloroplasts / large vacuole; bacterial cell lacks mitochondria.
5. Explain why a root hair cell may contain many mitochondria.[3]
Mitochondria are the site of aerobic respiration; respiration transfers/releases energy; energy is required for active transport of mineral ions against a concentration gradient.

Paper 6 · Alternative to Practical

A student places equal potato cylinders in sucrose solutions for 60 minutes.

Sucrose / mol dm⁻³Initial mass / gFinal mass / g% change
0.04.004.72+18.0
0.24.104.35+6.1
0.43.953.87−2.0
0.64.053.52−13.1
6(a). Estimate the concentration at which there is no net movement of water.[1]
Approximately 0.35 mol dm⁻³ (accept a sensible interpolation between 0.2 and 0.4).
6(b). Explain the decrease in mass at 0.6 mol dm⁻³ using water potential.[3]
The solution has lower water potential than the potato cells; water moves out of the cells; through partially permeable cell membranes by osmosis.
6(c). State two control variables and one improvement that increases reliability.[3]
Controls: time, temperature, initial cylinder dimensions/volume, potato source, solution volume. Reliability: repeat each concentration and calculate a mean (identify anomalies if appropriate).

Sources and teacher note

Cambridge IGCSE Co-ordinated Sciences 0654 syllabus for 2025–2027

Videos: Cognito cell structure, diffusion, osmosis and active transport; magnification calculation video linked in Lesson 2. Video links were checked during creation on 14 September 2026.

This independent learning resource is not endorsed by Cambridge International. Cambridge-style questions are original and are not copied from past papers.

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