Passive Transport

Overview

This is lesson 7 of 20 in the unit Transport Systems in Living Things. Students investigate diffusion as a passive transport mechanism using food colouring in water, then connect their observations to how substances move in cells and why transport systems are important in multicellular organisms.

Learning intentions

• WALT explain diffusion as a form of passive transport.
• WALT investigate how particles spread from a high concentration to a low concentration.
• WALT record observations and use evidence to explain what happened.
• WALT identify examples of passive transport in living things.

Success criteria

• I can define diffusion using the terms particles, concentration and movement.
• I can describe the pattern I observed in the food-colouring investigation.
• I can explain that diffusion does not require cellular energy.
• I can give a relevant real-life example of passive transport.

Curriculum links

• Transport systems in plants and humans: comparing substance movement in single-celled and multicellular organisms.
• Body Systems: explaining why multicellular organisms require transport systems to move substances efficiently.
• Human transport system: understanding osmosis as the passive movement of water across a selectively permeable membrane.
• Science capabilities: investigating, interpreting evidence, communicating explanations and evaluating ideas.

Lesson structure (60 minutes)

1. 0–5 min · Do Now. Display the starter question from the opening question slide: “If a drop of food colouring is placed in still water, how will it spread?” Students answer independently, draw a prediction and identify what they think will cause the movement.

2. 5–13 min · Share and teach. Use the diffusion teaching slides to gather predictions through think-pair-share, then introduce passive transport, diffusion, concentration gradient and equilibrium. Explain that diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, and that it does not require energy from the cell. Students annotate a simple particle diagram and ask questions.

3. 13–18 min · Practical briefing. Display the practical instructions and safety slide and model the first step. Place one drop of food colouring into a clear beaker of room-temperature water without stirring. Students work in groups of three, with roles for equipment manager, observer/timekeeper and recorder. Emphasise careful handling of glassware, no tasting, and immediate reporting of spills.

4. 18–33 min · Diffusion investigation. Distribute the diffusion investigation worksheet and provide each group with a beaker, water, food colouring and timer. Students record the starting appearance, observe at one-minute intervals, sketch or describe the spreading pattern, and note when the water appears evenly coloured. They must not stir the water. Circulate to question groups: “Where is the concentration highest?” and “What evidence shows that particles moved?”

5. 33–43 min · Analyse the evidence. Students complete the results and explanation questions on the diffusion investigation worksheet. They write a conclusion using the structure: “The food colouring moved from ___ to ___ because ___.” Pairs compare observations and discuss why groups may have recorded slightly different times, including differences in drop size, water temperature or observation judgement.

6. 43–54 min · Apply and discuss. Show the real-life examples and discussion prompts. Groups sort examples into “likely passive transport” and “not passive transport”, justifying each decision: oxygen entering cells, carbon dioxide leaving cells, perfume spreading through a room, water entering plant root cells, and glucose being moved through the bloodstream. Clarify that osmosis is the diffusion of water across a selectively permeable membrane, and connect this to plant health. Groups share one explanation with the class.

7. 54–60 min · Plenary and exit question. Use the plenary slide to display the exit question: “Explain how diffusion could help a cell obtain oxygen. Why is diffusion alone not enough to transport substances around a large multicellular organism?” Students answer independently in two or three sentences before handing in their worksheet.

Resources

• the passive transport slide deck
• the diffusion investigation worksheet
• Clear beakers or cups, one per group
• Room-temperature water
• Food colouring and droppers
• Timers or classroom clock
• Paper towels and waste container
• Safety glasses, if required by school procedures
• Board or visualiser

Assessment

• Listen to predictions and questioning during the Do Now and teaching discussion; identify misconceptions such as “particles stop moving at equilibrium”.
• Check group observations, particle diagrams and conclusions for correct use of concentration and evidence.
• Use the exit response to assess whether students can explain diffusion and the need for transport systems in larger organisms.

Differentiation

• Provide the practical as numbered, step-by-step instructions on the diffusion investigation worksheet, model the first step, and assign clear group roles.
• Support learners with a word bank, labelled particle diagrams, sentence starters and the option to record observations using drawings or speech-to-text.
• Use a dyslexia-friendly worksheet layout: clear sans-serif font, generous spacing, short instructions, high contrast and minimal text per section. Read key instructions aloud and allow students to work with a supportive partner.
• For EAL learners, pre-teach key terms with visuals and accept labelled diagrams before requiring full written explanations. Provide challenge prompts for students ready to extend their reasoning.

Extension

• Research osmosis and explain its importance in plant health, including what may happen to a plant cell in a very dilute or very concentrated solution.
• Design a fair investigation to test one factor affecting diffusion, such as water temperature, while identifying the independent, dependent and controlled variables.
• Explain why a single-celled organism can rely mainly on diffusion, whereas a large multicellular organism needs specialised transport systems.