IGCSE Biology: Movement Into and Out of Cells (Cambridge 0610)

Topic 3 of Cambridge IGCSE Biology (0610) covers the three ways substances cross a cell membrane: diffusion, osmosis and active transport. It follows directly from Topic 2: Organisation of the organism, which establishes cell structure, and is one of the shorter topics in the syllabus – but it underpins how you explain gas exchange, nutrient uptake and water balance in every topic that follows.

Where this topic sits

Extended (Supplement) candidates need all three sub-topics below; Core candidates studying for grades C-G can stop at the Core-only statements marked in each section. Both tiers are examined on Papers 1 and 3 (Core) or Papers 2 and 4 (Extended), plus the practical paper.

3.1 Diffusion

Core

• Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement.
• State that the energy for diffusion comes from the kinetic energy of random movement of molecules and ions.
• State that some substances move into and out of cells by diffusion through the cell membrane.
• Describe the importance of diffusion of gases and solutes in living organisms.
• Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance.

There is no Supplement-only content for diffusion – 3.1 is entirely Core, which makes it a reliable, high-value topic to secure fully regardless of which tier you’re sitting.

3.2 Osmosis

Core

• Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport.
• State that water diffuses through partially permeable membranes by osmosis.
• State that water moves into and out of cells by osmosis through the cell membrane.
• Investigate osmosis using materials such as dialysis tubing.
• Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations.
• State that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall.

Supplement

• Describe osmosis as the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.
• Explain the effects on plant cells of immersing them in solutions of different concentrations by using the terms: turgid, turgor pressure, plasmolysis, flaccid.
• Explain the importance of water potential and osmosis in the uptake and loss of water by organisms.

Osmosis is the sub-topic most likely to trip up Core candidates who have half-learned the Supplement definition: the Core-level statement only requires you to know that water moves by osmosis through a partially permeable membrane, not the higher/lower water potential language, which is Supplement-only.

3.3 Active transport

Core

• Describe active transport as the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (i.e. against a concentration gradient), using energy from respiration.

Supplement

• Explain the importance of active transport as a process for movement of molecules or ions across membranes, including ion uptake by root hairs.
• State that protein carriers move molecules or ions across a membrane during active transport.

Active transport is the shortest sub-topic in this unit, but it is also the one most often confused with diffusion in exam answers: the defining feature to state clearly is that active transport moves particles against a concentration gradient and requires energy from respiration, whereas diffusion and osmosis are both passive processes that need no energy input from the cell.

How the three processes compare

Process	Direction	Energy required?	Example use in organisms
Diffusion	High to low concentration	No (kinetic energy only)	Gas exchange in alveoli, small solutes crossing membranes
Osmosis	High to low water potential	No	Water uptake by root hairs, water balance in cells
Active transport	Low to high concentration	Yes (from respiration)	Ion uptake by root hairs, glucose reabsorption in the kidney

Examiners frequently set questions that ask you to identify which of the three processes is occurring in an unfamiliar context and justify the choice – being able to state the direction of movement and whether energy is required, from memory, is worth more in practice than being able to recite the definitions in isolation.

How to approach it

Learn diffusion and active transport as a contrasting pair first, since they move different particles in opposite directions relative to the concentration gradient, then treat osmosis as diffusion’s special case restricted to water moving across a partially permeable membrane. If you are entered for the Extended tier, practise applying the turgid/turgor pressure/plasmolysis/flaccid vocabulary to unfamiliar plant-tissue scenarios (for example, why a wilted plant recovers after watering), since this is where Supplement questions on osmosis are most often set. For the practical investigations, be ready to describe both the dialysis-tubing osmosis investigation and how you would measure the effect of surface area, temperature or concentration gradient on diffusion rate, since practical technique questions on this topic appear on the written papers as well as the practical paper.

Official syllabus

Cambridge International, Cambridge IGCSE Biology (0610) syllabus for examination in 2026, 2027 and 2028 (Version 3, published August 2026): official syllabus PDF, Subject content, section 3 “Movement into and out of cells”. Verified 2026-09-02.