| Explain the role of the membrane as a barrier with selective permeability | The phospholipids are tightly packed together, and the membrane has a hydrophobic interior which causes the membrane to be selectively permeable. A membrane that has selective permeability allows certain molecules (lipid soluble) and block other molecules (large polar molecules) from moving freely though the cell membrane. |
| Describe the role of facilitated diffusion (uniporter) in regulating cell function | Transported molecule binds to a specific binding site on a carrier exposed to one side of the membrane. Binding results in in a conformational change of the carrier protein which exposes transported molecule to the other side of the membrane. The rate of the carrier-mediated transport is much slower, compared to the passage of ions through an ion channel pore. |
| Describe the role of primary active transport (pumps) in regulating cell function | In primary active transport, the carrier splits ATP to move a substance against its concentration gradient. Energy in the form of ATP is required to vary the affinity of the binding site when it is exposed on opposite sides of the plasma membrane. |
| Describe the role of secondary active transport (cotransporters) in regulating cell function | In secondary active transport, the carrier does not directly split ATP. Instead, it utilises the potential energy in the Na+ gradient. Movement of Na+ into the cell down its concentration gradient drives the uphill transport of another solute by a secondary active-transport carrier. |
| Describe the role of secondary active transport (counter transporters) in regulating cell function | Counter-transporters utilise the same mechanism of transport as cotransporters but the solute and Na+ move through the membrane in opposite directions. |
| Describe the role of Potassium (K+) ion channels in regulating cell function | K+ channels function to restore and maintain a resting membrane potential K+ “leak” channels are active at rest and maintain negative resting membrane potential |
| Describe the role of Sodium (Na+) ion channels in regulating cell function | Na+ channels cause excitatory responses Voltage gated Nav channels open rapidly in response to membrane depolarisation. Na+ entering the cell through Nav channels cause further membrane depolarization (positive feedback loop in action potential) |
| Describe the role of Calcium (Ca2+) ion channels in regulating cell function | Ca2+is an important second messenger, coupling stimuli to responses Voltage-gated Ca2+channels open in response to membrane depolarization, contributing to action potentials in neurons and cardiac muscle |
| Explain the ionic basis of the resting membrane potential | Ions are electrically charged chemical forces which move down the concentration gradient. The direction of ion movement across the plasma membrane depends on: concentration gradient and voltage gradient (membrane potential) In order for memebrane potential to be establidhed there must be: Symmetric distribution of ions across the plasmamembrane (i.e., ion concentration gradients) Selective ion channels in the plasma membrane. |
| Define osmosis and osmotic pressure | Osmosis: the flow of warer molecules through a semipermiable memerbane from a region of high solute concetration, until equilibrium is esablished Osomotic Pressure: pressure required to counter osmosis. |
