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Detailed notes on Movement into and out of Cells for Cambridge IGCSE Biology, covering key concepts, explanations, examples, and exam-focused revision points.
Movement of particles AGAINST a concentration gradient, using ATP from respiration and specific protein carriers. The cell's way of accumulating substances even when concentrations outside are low.
Mapped to the Cambridge IGCSE 0610 syllabus (2026-2028).
Against gradient + ATP + protein carriers. All three for full marks.
Cambridge definition (Extended):
"Movement of particles through a cell membrane from a region of LOWER concentration to a region of HIGHER concentration (AGAINST the concentration gradient), using ENERGY from respiration and PROTEIN CARRIER molecules."
Three keywords Cambridge marks:
Where the energy comes from. ATP is generated by respiration in mitochondria. Cells with lots of active transport (e.g. root hair cells, kidney tubule cells, gut lining cells) have MANY MITOCHONDRIA to supply ATP.
How it works (simplified).
Specificity. Each carrier protein only handles ONE type of substance (like a key fits one lock). Different ions need different carriers.
Direction, energy, mechanism — three big differences.
| Feature | Diffusion | Active transport |
|---|---|---|
| Direction | Down concentration gradient (high → low) | Against (low → high) |
| Energy from cell? | NO (passive) | YES (ATP) |
| Mechanism | Random molecular motion | Specific protein carriers |
| Speed | Limited by gradient | Limited by carriers + ATP supply |
| Stopping condition | Equilibrium | When ATP runs out or carrier saturated |
| Examples | Gas exchange in alveoli; CO₂ to chloroplasts | Mineral uptake by roots; glucose reclamation in kidneys |
Worked qualitative. A respiring root cell suddenly has its O₂ supply cut. What happens to mineral uptake?
Worked qualitative. Why does diffusion not get a cell as much glucose as it needs sometimes?
Cambridge tip. When asked "why is active transport important?", give an example: "Root cells use active transport to take up mineral ions like nitrates from soil — the soil concentration is usually lower than inside the cell, so diffusion would not work."
Roots, kidneys, intestines — wherever cells need to accumulate substances against a gradient.
1. Root hair cells absorbing mineral ions from soil.
2. Kidney tubules reclaiming glucose.
3. Glucose absorption in the small intestine.
4. Sodium-potassium pump in nerve cells.
Worked qualitative. Why are root hair cells so rich in mitochondria? They do a lot of active transport (mineral ion uptake), which needs continuous ATP. Many mitochondria → high ATP supply → high transport rate → cells absorb minerals efficiently.
Verbatim phrases and definitions Cambridge mark schemes credit.
Active transport appears every Paper 4 (4-6 marks): define, distinguish from diffusion, give examples. Examiner reports flag students missing 'protein carrier' from the definition and saying active transport is faster than diffusion (it's not — direction is the key, not speed).
Sources: Cambridge IGCSE Biology 0610 syllabus 2026-2028 (3.3); 0610/42 May/Jun 2024 — Q6 (active transport); 0610 Examiner Reports 2022-2024. Last reviewed 2026-05-07.
Step-by-step solutions to past-paper-style questions on active transport, written exactly the way a tutor would explain them at the board.
Question
Give the Cambridge Extended definition of active transport.
Step-by-step solution
Step 1
MOVEMENT of particles through a CELL MEMBRANE.
Step 2
From a region of LOWER concentration to a region of HIGHER concentration (AGAINST the concentration gradient).
Step 3
Using ENERGY released by respiration.
Step 4
Through PROTEIN CARRIER molecules in the membrane.
Answer
The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against the concentration gradient), using energy from respiration and protein carrier molecules.
Examiner tip
Four marking points: against the gradient, energy from respiration, membrane, protein carrier.
Question
For each, state whether it is diffusion or active transport: (a) oxygen entering a cell down its gradient; (b) mineral ions entering a root hair cell from soil where they are at lower concentration; (c) carbon dioxide leaving a respiring cell.
Step-by-step solution
Step 1
(a) Oxygen moves DOWN its gradient with no energy needed → diffusion.
Step 2
(b) Ions move AGAINST the gradient (lower outside to higher inside) → this needs energy → active transport.
Step 3
(c) CO₂ moves DOWN its gradient out of the cell → diffusion.
Answer
(a) Diffusion; (b) active transport; (c) diffusion.
Examiner tip
The test is the direction relative to the gradient: down the gradient = diffusion; against the gradient = active transport.
Question
Compare active transport with diffusion using THREE differences.
Step-by-step solution
Step 1
Direction: diffusion = down the gradient; active transport = AGAINST the gradient.
Step 2
Energy: diffusion = no metabolic energy needed (passive); active transport = REQUIRES energy from respiration (ATP).
Step 3
Mechanism: diffusion = particles move randomly through the membrane; active transport = via specific PROTEIN CARRIERS.
Answer
Diffusion: down the gradient, passive, random. Active transport: against the gradient, uses energy from respiration, via protein carriers.
Question
Give THREE examples of active transport in living organisms.
Step-by-step solution
Step 1
Mineral ion uptake by root hair cells — ion concentrations in soil are usually lower than in the cell, so uptake is against the gradient.
Step 2
Reabsorption of glucose from the kidney tubule back into the blood, even when tubule glucose is lower than blood glucose.
Step 3
Absorption of glucose and amino acids from the small intestine into the blood when their concentration in the gut is lower than in the blood.
Answer
Mineral uptake by roots; glucose reabsorption in the kidney; glucose/amino acid absorption in the small intestine at low concentrations.
Question
Root tissue takes up potassium ions from a solution. When the oxygen supply is increased, the rate of uptake increases; when a respiratory poison (such as cyanide) is added, uptake almost stops. Explain how these results show that the ions are taken up by active transport.
Step-by-step solution
Step 1
Active transport requires energy released by respiration, and aerobic respiration needs oxygen.
Step 2
When more oxygen is supplied, respiration speeds up, releasing more energy, so the rate of ion uptake rises — showing uptake depends on respiration.
Step 3
A respiratory poison such as cyanide stops respiration, so no energy is released; uptake almost stops — confirming the ions cannot be taken up without respiratory energy.
Step 4
If the ions were entering only by diffusion, changing oxygen or adding a respiratory poison would have little effect, because diffusion does not use respiratory energy. So the dependence on respiration proves it is active transport.
Answer
Uptake rises with more oxygen (more respiration → more energy) and almost stops with a respiratory poison (no energy). Since diffusion would be unaffected by either, the dependence on respiration shows the ions are moved by active transport.
Examiner tip
The reasoning examiners want: active transport needs respiratory energy, so anything affecting respiration affects uptake — unlike diffusion.
Question
Compare diffusion, osmosis and active transport in terms of what moves, the direction of movement, and whether energy from respiration is needed.
Step-by-step solution
Step 1
Diffusion: any particles (e.g. O₂, CO₂); move DOWN the concentration gradient (high → low); no respiratory energy needed (passive).
Step 2
Osmosis: only WATER molecules; move from higher to lower water potential through a partially permeable membrane (down the water potential gradient); no respiratory energy needed (passive).
Step 3
Active transport: particles such as ions, glucose; move AGAINST the concentration gradient (low → high); requires energy from respiration and protein carriers.
Step 4
So the key difference is that active transport works against the gradient and needs respiratory energy, while diffusion and osmosis are passive and work down a gradient.
Answer
Diffusion: any particle, down the gradient, passive. Osmosis: water only, down the water potential gradient through a partially permeable membrane, passive. Active transport: ions/molecules, against the gradient, needs respiratory energy and protein carriers.
Examiner tip
A clear three-way comparison along the same criteria (what moves / direction / energy) is exactly what higher-mark answers do.
High-scoring sample answers for active transport on the Cambridge IGCSE 0610 paper, with examiner-style notes mapping each response to the mark scheme and assessment objectives.
State where the energy for active transport comes from. (1 mark)
Model answer
From respiration (which releases energy / ATP).
Why this scores
One mark for 'respiration' (or energy/ATP from respiration). 'Energy' alone, without the source, is risky.
State two differences between active transport and diffusion. (2 marks)
Model answer
Active transport moves particles against the concentration gradient (from low to high concentration), whereas diffusion moves them down the gradient (from high to low). Active transport also requires energy from respiration, whereas diffusion does not (it is passive).
Why this scores
Two genuine contrasts, each comparing both processes. Direction and energy are the safest points.
Define active transport. (3 marks)
Model answer
Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against the concentration gradient), using energy from respiration and protein carrier molecules.
Why this scores
Three marks: (1) through a cell membrane; (2) against the concentration gradient / low to high; (3) using energy from respiration. Mentioning protein carriers strengthens the answer.
Explain how mineral ions are taken up from the soil into a root hair cell by active transport. (4 marks)
Model answer
The concentration of mineral ions is usually lower in the soil water than inside the root hair cell, so the ions must move against their concentration gradient, which diffusion cannot do. The ions are moved across the cell membrane by protein carrier molecules. This requires energy released by respiration in the cell's many mitochondria. Because energy is used, the ions can be taken in even though they are moving from a lower to a higher concentration.
Why this scores
Four marks: ions lower in soil than cell / against gradient; carried by protein carriers in the membrane; energy from respiration (mitochondria); so uptake occurs against the gradient.
In an experiment, root tissue was placed in a potassium ion solution. The rate of ion uptake was measured at different oxygen concentrations and then after adding a respiratory poison. Uptake increased as oxygen increased, and fell almost to zero when the poison was added. Explain what these results show about how the ions are absorbed. (5 marks)
Model answer
The results show the ions are absorbed by active transport, which uses energy from respiration. As the oxygen concentration increased, the rate of aerobic respiration increased, releasing more energy, so more energy was available for active transport and the rate of ion uptake rose. When the respiratory poison was added, respiration stopped, so no energy was released and uptake fell almost to zero. If the ions had been entering only by diffusion, neither the oxygen level nor the respiratory poison would have changed the rate, because diffusion does not use respiratory energy. Because uptake clearly depends on respiration, the ions must be taken up by active transport, against their concentration gradient.
Why this scores
Five marks across: identifies active transport; more oxygen → more respiration → more energy → faster uptake; poison stops respiration → uptake stops; diffusion would be unaffected; conclusion that uptake depends on respiration. Reward use of the data trend.
Compare diffusion, osmosis and active transport. In your answer, refer to what moves, the direction of movement and whether energy from respiration is required. (6 marks)
Model answer
In diffusion, any small particles (such as oxygen or carbon dioxide) move from a region of their higher concentration to a region of their lower concentration, i.e. down the concentration gradient, and no energy from respiration is needed because the particles move using their own random kinetic energy. In osmosis, only water molecules move, from a region of higher water potential to a region of lower water potential through a partially permeable membrane — again down a gradient and without respiratory energy, so osmosis is a special case of diffusion. In active transport, particles such as mineral ions or glucose are moved against the concentration gradient, from a region of lower concentration to a region of higher concentration, through protein carrier molecules in the membrane, and this does require energy from respiration. So diffusion and osmosis are passive and move substances down a gradient, while active transport is the only one that uses respiratory energy to move substances against the gradient.
Why this scores
Up to 6 marks for comparing all three along the three criteria: what moves (any particle / water only / ions and molecules); direction (down / down water-potential / against gradient); energy (none / none / from respiration). A clear concluding contrast is rewarded.
Definitions to memorise and the exact keywords mark schemes credit for active transport answers — sharpened from recent examiner reports for the 2026 0610 sitting.
Movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, using energy from respiration and via protein carrier molecules.
Energy released by respiration (especially in mitochondria) and used to power active transport, muscle contraction, protein synthesis, etc.
A membrane protein that binds specific molecules or ions and uses energy from respiration to move them across the cell membrane against a gradient.
The traps other students keep falling into on active transport questions — taken from recent Cambridge IGCSE 0610 examiner reports and mark schemes — and how to avoid them.
Why it happens
Students associate 'active' with 'fast'.
How to avoid it
Active means AGAINST the gradient (from low to high concentration). Speed isn't the defining feature — direction and energy use are.
Why it happens
Students focus on 'against gradient' and 'energy'.
How to avoid it
Cambridge mark schemes give a separate mark for 'protein carriers' or 'transport proteins'. Always include.
Why it happens
Anything involving membranes might seem active.
How to avoid it
Active transport REQUIRES energy from respiration. Osmosis is PASSIVE — it does not use respiratory energy.
The things students keep getting wrong in this sub-topic, answered.