Pearson Edexcel International GCSE Biology · specification 4BI1 · Paper 1 | Whole paper: Core content, all five topics · Free · no account needed
2(d) Movement of substances into and out of cells (4BI1 specification)
Three ways substances cross a membrane, and the one that costs the cell energy.
Learn it on Incandio
The 3 Incandio pages that teach this — each explained in full, then proved in marked questions, taught back to an AI pupil and defended in a debate. Completely free.
- Enzymes and pH — Why acid ruins one enzyme and is the only condition another will work in — and how to find an enzyme's best pH by experiment.
- Diffusion, Osmosis and Active Transport — The three ways anything gets into or out of a cell — which need energy, which do not, and what makes each one fast or slow.
- Photosynthesis — How a plant builds itself out of air, where the energy for that comes from, and the one job the soil is actually doing.
The teaching route this belongs to: Topic 2 · Structures and functions in living organisms (Biology) — the lessons in order, with every gate.
Specification coverage
Topic 2 Structures and functions in living organisms (d) Movement of substances into and out of cells — statements 2.13–2.19
Assessment objectives: AO1, AO2, AO3. Suggested learning time: 70 minutes.
Required knowledge
- Diffusion, osmosis and active transport as means of transport across membranes
- Osmosis as the net movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane
- Active transport as movement against a concentration gradient, requiring energy from respiration
- The factors affecting the rate of movement: surface area, temperature, concentration gradient and distance
Required skills
- Choose the correct process for a described situation
- Explain results from an osmosis investigation using potato or visking tubing
- Calculate percentage change in mass
- Describe and evaluate the required practical: Investigate osmosis, for example using potato tissue in a range of sucrose concentrations, and calculate percentage change in mass.
How it is examined
- Multiple-choice and short-answer recall
- Application of the content to an unfamiliar context
- Extended open-response, marked on the quality of a connected explanation
- Practical questions on method, variables, data and sources of error
Common mistakes
- Saying water moves 'from high to low concentration' without saying concentration of what. Water moves from a dilute solution to a concentrated one — that is, from high water potential to low.
- Describing osmosis as a type of active transport. It is passive and requires no energy.
- Reporting a change in mass rather than a percentage change, which removes the effect of different starting masses.
This page maps the specification. The pages above teach it, and the Biology lessons hold the whole course — completely free.