Cell Membrane Functions

Overview

Today’s focus is how the cell membrane controls what enters and leaves the cell. Students will model permeability and explain why the membrane is selectively permeable for maintaining homeostasis in living things.

Learning intentions

• Students will describe the cell membrane as a selectively permeable barrier.
• Students will compare diffusion, osmosis, and active transport as transport mechanisms.
• Students will explain how transport supports cell survival and cell function.
• Students will use models and evidence to justify claims about membrane permeability.

Success criteria

• I can define permeability and selective permeability in my own words.
• I can explain how diffusion and osmosis move materials based on concentration differences.
• I can describe active transport as energy-requiring movement against a concentration gradient.
• I can use a model to predict which substances enter or leave a cell and why.

Curriculum links

• Ontario Science and Technology: Understanding life systems through basic cell structures and their functions.
• Scientific inquiry and communication: Using evidence, models, and reasoning to answer questions.
• Skills for addressing problems: Connecting mechanisms to outcomes in systems (cells maintaining conditions).
• Environmental and technological literacy (light connection): Relating transport to real biological processes.

Lesson structure (45 minutes)

1. 5 min — Starter: “Door or Filter?”

• Prompt students with: “Is the cell membrane a door or a filter?” Students do a quick pair share and write one sentence justification.
• Teacher listens for misconceptions such as “anything can pass freely.”

2. 8 min — Mini-lesson: Selective permeability

• Teach using simple diagrams of a cell with different-sized molecules and “allowed vs blocked” pathways.
• Clarify that the membrane regulates movement to protect the cell while still allowing needed substances in.

3. 10 min — Build and test a model

• Students receive a simple hands-on model (e.g., cut-out membrane with holes of different sizes plus “molecules” cards).
• In small groups, they test which items can pass through under different conditions (size/charge/specific “channels” provided by the teacher).
• Groups record observations: which “substances” entered, which stayed out, and any pattern.

4. 7 min — Transport mechanisms stations (rotation)

• Three short stations with teacher-directed prompts:
• Diffusion: particles move from higher to lower concentration.
• Osmosis: water moves to balance solute concentrations (through a membrane).
• Active transport: movement requires energy and can move against the gradient.
• Students complete a brief “Claim–Reason–Model” note for each station.

5. 8 min — Guided practice: Case study

• Present a scenario (e.g., a cell in fresh water vs a salty environment) and ask: “Predict what happens to water movement and how the cell responds.”
• Whole-class discussion using student evidence from stations.

6. 5 min — Exit ticket: Explain and predict

• Students answer two questions:
• “Why is selective permeability important for cells?”
• “Which transport mechanism fits this statement: ‘Particles move from low to high concentration’—and why?”
• Collect to check understanding of diffusion/osmosis/active transport.

Resources

• Cell membrane diagram handout (teacher-made or textbook page)
• “Membrane model” materials (paper/card membrane, fasteners, elastic or tape, hole templates)
• Particle/molecule cards (different sizes; optional “water” and “salt/solute” cards)
• Station cards or slides describing diffusion, osmosis, active transport scenarios
• Student recording sheet with short sections: Observation, Pattern, Claim–Reason–Model
• Highlighters or coloured pens for marking key words (selective, concentration, energy)
• Exit ticket slips or worksheet
• Visual supports for ESL learners: sentence frames and word bank (diffusion, osmosis, active transport, concentration, energy)

Assessment

• Formative assessment through the starter discussion and teacher listening for misconceptions.
• Station notes using “Claim–Reason–Model” to evaluate understanding of each mechanism.
• Exit ticket to assess key concepts: selective permeability and correct mechanism identification.

Differentiation

• Support (scaffolded language): Provide sentence frames such as “The membrane is selective because…”, “Diffusion happens when…”, “Active transport is needed when…”
• Support (visuals): Use clear diagrams and colour-coding for concentration gradients; provide model steps in numbered format.
• ESL: Allow students to explain with partner rehearsal before writing; offer bilingual glossaries if available; accept oral responses in addition to written responses where appropriate.
• Extension (deeper reasoning): Challenge students with a “What if?” prompt (e.g., “What would happen if the membrane stopped working?”) and require an evidence-based explanation using transport mechanisms.