Diffusion and Osmosis

Overview

In this lesson, students build understanding of diffusion and osmosis by observing them in simple, safe experiments using substances that model movement of particles across barriers. They connect the observations to cell-like systems and explain why water and dissolved substances move.

Learning intentions

• Students will be able to describe diffusion in terms of particle movement from areas of higher concentration to lower concentration.
• Students will be able to describe osmosis as the diffusion of water through a partially permeable membrane.
• Students will be able to record and interpret experimental observations and link them to the processes.
• Students will use scientific reasoning to explain how these processes relate to cells.

Success criteria

• I can explain diffusion using a particle model and concentration gradient language.
• I can explain osmosis as water movement through a partially permeable barrier.
• I can record measurements/observations and use them to support my explanation.
• I can communicate my findings clearly using science vocabulary (concentration, partially permeable, water movement, diffusion).

Curriculum links

• Scientific inquiry skills: planning, conducting, and interpreting investigations; recording observations; using evidence to draw conclusions.
• Cells and systems: understanding how structures and processes help cells survive; relating cell processes to transport of substances.
• Science communication: using appropriate terminology and clear explanations of experimental results.
• Understanding matter and energy connections: linking particle behaviour to observable changes.

Lesson structure (45 minutes)

1. 5 min – Starter (Do Now) Students view/think about a simple scenario: “A drop of food colouring in water spreads over time—why?” Students write 2–3 sentences or a quick sketch using the terms concentration and movement. Teacher collects 3–4 responses.

2. 8 min – Mini-lesson: Particle models Teacher presents a visual particle model of diffusion (particles spreading out) and osmosis (water moving through a barrier). Emphasise: diffusion involves dissolved particles; osmosis involves water specifically; osmosis needs a partially permeable membrane. Students complete a quick “Process Match” on scrap paper: statement → diffusion or osmosis.

3. 7 min – Safety, materials, and prediction In groups, students review experimental steps and safety rules. Teacher models how to label cups, track times, and measure/observe consistently. Each group makes a prediction: which cup will show more change and whether the change indicates diffusion or osmosis.

4. 15 min – Hands-on investigation (stations or one setup) Students conduct an experiment showing diffusion and osmosis. Example options (choose one set to run today):

• Diffusion: food colouring in water (or potassium permanganate in water) and compare rates by water temperature or concentration.
• Osmosis: model membrane using a barrier such as a semi-permeable setup (e.g., dialysis tubing/safer classroom equivalent) with solutions of different concentration; monitor change such as mass or visible volume. Students record observations at set intervals (e.g., every 3–5 minutes) and include a time log. Teacher circulates, prompting with questions: “What changed first? What stayed the same? What does that suggest about movement?”

5. 5 min – Data check and interpretation Groups share one key observation and one data point. Teacher helps students interpret what the evidence means: diffusion vs osmosis, and direction of movement (higher to lower concentration; water toward more concentrated solution).

6. 3 min – Science communication (exit mini-write) Students complete an “Evidence-Explanation” response: “Based on my observations, diffusion/osmosis occurred because…” Require one piece of evidence from their table and one sentence using a scientific term.

7. 2 min – Consolidation Teacher previews the link to the next lesson: how transport supports cell survival and why membranes matter. Students clean up and turn in observation sheets.

Resources

• Student lab handouts with prediction, observation table, and conclusion frames
• Cups/beakers, stirring sticks, measuring cups (as appropriate)
• Food colouring (for diffusion) and clear water
• Semi-permeable barrier materials (for osmosis) and two solutions of different concentration (prepared ahead)
• Labels/marker for each cup/tubing
• Measuring tools: ruler or scale (if measuring mass/volume), timer
• Gloves and eye protection as required by the school lab policy
• Paper towels, waste containers, and a simple class “science voice” rubric (listen, use evidence, respectful discussion)
• Access to visuals/diagram cards of diffusion/osmosis particle models

Assessment

• Formative checks during the mini-lesson: “Process Match” accuracy and vocabulary use.
• During investigation: teacher observation of group recording quality (time, repeated observations, clarity).
• Exit mini-write: evidence-based explanation using correct terms (diffusion vs osmosis, direction of movement, and membrane role).

Differentiation

• Support (ESL/learning needs): provide sentence frames for predictions and conclusions (e.g., “I predict that…, because…”). Offer word banks with pictorial supports (concentration gradient, partially permeable, water).
• Support (hands-on roles): assign roles in each group (timekeeper, measurer/recorder, materials manager, reporter) to reduce cognitive load.
• Extension (fast finishers): ask students to propose a modification to improve reliability (more trials, control variables like temperature/initial concentration) and predict how results would change.
• EAL/SEN: allow oral explanation option paired with a short written response; accept drawings with labels plus one sentence; pre-teach key terms using student-friendly definitions and gestures/visuals.
• Language and equity: encourage students to use home languages in brainstorming, then translate key ideas into English during reporting.

Unit/lesson breakdown (Exploring the World of Cells)

• Lesson 1: Introduction to cells and microscope basics
• Lesson 2: Cell structures and functions (nucleus, membrane, organelles)
• Lesson 3: Comparing plant and animal cells
• Lesson 4: Cell transport overview (why materials must move)
• Lesson 5: Passive vs active transport (big picture)
• Lesson 6: Membranes as barriers (selective permeability)
• Lesson 7: Diffusion (particle model and everyday examples)
• Lesson 8: Osmosis (water movement and water potential ideas)
• Lesson 9: Practice with concentration gradients (data interpretation)
• Lesson 10: Lab planning skills (controls, variables, reliability)
• Lesson 11: Student lab investigations (teacher-supported)
• Lesson 12: Understanding Diffusion and Osmosis (this lesson)
• Lesson 13: Transport in cells—linking to real organisms
• Lesson 14: Review and consolidation (concept mapping and practice)
• Lesson 15: Unit assessment and reflection