Movement across membranes explains how cells take in what they need and lose what they do not. This page shows the order of the lessons and where your next study session should start.
The chapter sits in SPM Biology after cells and organisation. It leads into leaves and photosynthesis, where gases and water cross membranes.
How do the four lessons connect?
Start with the comparison of the three processes, because later lessons use the same words.
- Comparing diffusion, osmosis and active transport separates them by direction and energy.
- Predicting cells in different solutions applies osmosis to cells.
- Explaining concentration gradients gives the idea behind every direction you state.
- Interpreting membrane-transport experiment data reads results tables.
What is the core idea in one example?
Direction comes from comparing two concentrations. Here is a worked example. A cell holds a solution with 20 units of solute, and the surrounding solution has 5 units.
The surroundings have less solute, so the water concentration outside is higher. Water therefore moves into the cell by osmosis. Solute would move out by diffusion if the membrane allowed it. Stating both directions, with the reason, is what the marks ask for.
Where should you start?
Start with the weakest last answer.
- You swap the three process names: open the comparison lesson.
- You cannot say whether a cell swells or shrinks: open the prediction lesson.
- Your direction statements lack a reason: open the gradient lesson.
- Tables of results confuse you: open the experiment data lesson.
- You want a full check: try the movement across membranes practice set.
Can one-to-one lessons help here?
They help when a student can define the terms but mixes them up on a new diagram. A teacher can draw a fresh situation and ask for direction and reason, step by step. See online one-to-one Biology tuition.