Membranes and Transport

Overview

In lesson 9 of the unit, students connect membrane structure with the movement of substances into and out of cells. They revise cell structures, learn the fluid mosaic model and compare four transport processes before planning a safe investigation into membrane transport.

Learning intentions

Students will:

• Describe how the fluid mosaic model explains plasma membrane structure.
• Distinguish diffusion, osmosis, facilitated diffusion and active transport.
• Formulate a testable question and identify independent, dependent and controlled variables.
• Identify and apply risk controls when handling biological materials.

Success criteria

• I can label and explain the roles of phospholipids, proteins, cholesterol and carbohydrates in a plasma membrane.
• I can compare the direction of movement, energy requirement and membrane proteins involved in four transport processes.
• I can write a testable question and correctly identify the variables.
• I can select suitable risk controls for a membrane transport investigation.

Curriculum links

• Cells as the basis of life: cell structures and functions, cells and their environments, and biochemical processes.
• Students explain how cell structures enable biological processes needed for life.
• Students explain how cells contribute to complex multicellular organisms by linking membrane transport to cell function and homeostasis.
• Working scientifically: questioning, planning investigations, identifying variables and applying safe laboratory practices.

Lesson structure (60 minutes)

1. 0–5 min · Hook and retrieval. Open with the membrane hook and retrieval slides showing a cell in a salty environment and ask, “Why might a cell shrink?” Students complete a three-question retrieval task in pairs: name two cell structures, state one function of the plasma membrane and predict what happens to a cell in a concentrated solution. Take brief responses and identify misconceptions.

2. 5–17 min · Fluid mosaic model. Use the fluid mosaic model slides to explicitly teach the phospholipid bilayer, hydrophilic heads, hydrophobic tails, embedded proteins, cholesterol and carbohydrate chains. Students annotate the membrane diagram on the membrane structure and transport worksheet and write one sentence explaining how the bilayer acts as a selectively permeable barrier. Emphasise that structure enables control of the cell’s internal environment.

3. 17–30 min · Transport comparison. Present the transport comparison slides and model each process: simple diffusion, osmosis, facilitated diffusion and active transport. Students complete the comparison table on the worksheet, recording the direction of movement, whether energy is required, whether a membrane protein is involved and one biological example. Pause after each process for a whole-class check using “move, no move” and “energy, no energy” hand signals.

4. 30–40 min · Apply and explain. Display the transport scenario slides with four short scenarios, such as oxygen entering a cell, water moving across a membrane, glucose using a carrier protein and mineral ions entering a root cell against a concentration gradient. Pairs classify each process and justify one answer using the terms “concentration gradient”, “selectively permeable” and “ATP”. Cold-call a range of students and correct the common misconception that all movement across membranes requires energy.

5. 40–53 min · Investigation planning and safety. Introduce a proposed investigation using potato cylinders or another approved biological material to examine how solution concentration affects mass or length. Distribute the membrane investigation planning section. In groups of four, students formulate a question, prediction and method outline, then identify the independent variable, dependent variable and at least three controlled variables. Use the investigation and safety slides to establish controls: wear eye protection, use clean equipment, handle biological material with forceps or gloves, disinfect benches, wash hands, manage spills and dispose of material as directed. Groups conduct a risk check and share one control with the class. The practical investigation is conducted in the following lesson.

6. 53–60 min · Plenary and exit check. Return to the plenary slides and revisit the hook question. Students complete the worksheet exit ticket: define osmosis, explain why active transport requires energy, and write one testable question for the proposed investigation. Collect responses to identify students needing support before the practical lesson.

Resources

• the membrane transport teaching deck
• the membrane structure and transport worksheet
• Projector or interactive display
• Whiteboard and markers
• Sample potato cylinder or photograph of potato cylinders in solutions
• Approved biological-material handling equipment for teacher demonstration
• Eye protection, disposable gloves and disinfectant for safety demonstration
• Access to the laboratory risk-assessment procedure

Assessment

• Check annotated membrane diagrams and questioning during direct teaching for accurate structure–function links.
• Review group investigation questions and variable identification, requiring revision where questions are not measurable or variables are unclear.
• Use the exit ticket to assess distinctions among transport processes and readiness for the practical investigation.

Differentiation

• Provide a partially labelled membrane diagram, a transport comparison word bank and sentence starters such as “The substance moves from… because…”.
• Use colour coding consistently: concentration gradient, membrane proteins and ATP are each represented by a different colour on the slides and worksheet.
• Allow EAL/D students to rehearse explanations with a partner and provide definitions for “gradient”, “permeable”, “carrier” and “energy”.
• Extend capable students by asking them to predict how changing temperature or membrane surface area could affect the investigation and to justify the prediction.