BRAINCAKECell Transport Mechanisms
Revision notes for Cell Transport Mechanisms in Edexcel Biology (8BI0). Read the start of any lesson here, then sign in free for the whole lesson, the R.E.C.I.P.E. recall steps and the quiz.
- The Need for TransportEvery living cell must exchange substances with its surroundings to stay alive.
- Transport Across the Cell MembraneThe cell surface membrane is partially permeable: it lets some substances through but not others.
- Passive and Active TransportSubstances cross cell membranes either by passive transport or by active transport.
- DiffusionDiffusion is the net movement of particles (molecules or ions) from a region of higher concentration to a region of lower concentration, down a…
- Facilitated DiffusionFacilitated diffusion is the passive movement of molecules or ions down their concentration gradient through specific membrane proteins.
- Water Potential ψWater potential, symbol ψ (the Greek letter psi), is a measure of the tendency of water molecules to move out of a solution.
- OsmosisOsmosis is the net movement of water molecules across a partially permeable membrane, from a region of higher water potential to a region of lower…
- Modelling OsmosisOsmosis can be modelled in the laboratory using Visking tubing (dialysis tubing).
- Osmotic ConcentrationsSolutions can be described by comparing their water potential with that of a cell: • Isotonic: the solution has the same water potential as the…
- Osmosis in Animal CellsAnimal cells are surrounded only by a cell surface membrane.
- Water Potential in Plant CellsPlant cells behave differently from animal cells in osmosis because of their structure: • a strong, fully permeable cellulose cell wall, which…
- Osmosis in Plant CellsWhen plant cells are placed in solutions of different water potential, water moves by osmosis, but the cell wall changes what happens.
- Turgor Pressure (P)Turgor pressure (P) is the pressure exerted by the protoplast (the cell contents) pushing outwards against the cell wall.
- Osmotic Potential (π)Osmotic potential (π) is the part of water potential that is due to dissolved solutes.
- Water Potential, Turgor Pressure and Osmotic PotentialThe water potential of a plant cell has two parts: the effect of the solutes and the effect of the pressure of the cell wall.
- Active TransportActive transport is the movement of molecules or ions across a membrane from a region of lower concentration to a region of higher concentration…
- Evidence for Active TransportSeveral lines of evidence show that some substances enter cells by active transport rather than by diffusion.
- Endocytosis and ExocytosisSome molecules and particles are far too large to pass through channel or carrier proteins.