What are the requirements for life: supply of replicators- self-reproducing molecules, replicator copy must be subject to error, supply of free energy for metabolism/growth/reproduction/movement, partial isolation from external environment. Selection is really important allows for the ability of different concentration of material to be found on different sides of the membrane. composed of 3 macromolecules: lipids www. notesolution. com. are insoluble in water: non polar hydrocarbon molecules go away from water, held by weak hydrophobic forces. Fluidity: crucial for function due to lipid, phospholipid can move laterally within the bilayer. move, flip: types of hydrocarbon tails (unsaturated) less packed- leaky ; vegetable oil saturated fatty acid tail (more packed, steroid cholesterol. has different effect on membrane fluidity at differ temp www. notesolution. com. Final exam notes biology: good cholesterol made by body to keep membrane secure, packs the spaced in unsaturated membrane, membranes are more dynamic at temp; cholesterol fills the space to prevent too much movement.