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II.active processes – cellular energy is used to drive the substance “uphill”against its concentration and electrical gradient. Cellular energy used isusually ATP. i.e. active transport.a.Vesicles – tiny, spherical membrane sacs that can be used by othersubstance to enter and leave cells.III.Diffusion – is a passive process in which the random mixing of particles ina solution occurs because of the particles’ kinetic energy.a.Solutes – dissolved substance.b.Solvents – the liquid that does the dissolving.IV.factors that influence diffusion rate
a.steepness of the concentration gradient – the greater thedifference in concentration between two side of the membrane, thehigher is the rate of diffusion.b.Temperature – the higher the temperature, the faster the rate ofdiffusion. i.e. feverc.mass of the diffusing substance – the larger the mass of thediffusing particle, the slower its diffusion rate.d.surface area – the larger the membrane surface area available fordiffusing, the faster is the diffusion rate. i.e. air sacs of lungs havelarge surface area for oxygen diffusion into the blood, but ifaffected by lung diseases, it reduce the surface area, slowing theoxygen diffusion rate which results to difficulty breathing.e.diffusion distance – the greater the distance over which diffusionmust occur, the longer it takes. i.e. diffusion across plasmamembrane only takes a fraction of a second because themembrane is so thin.V.simple diffusion – passive process in which the substances move freelythough the lipid bilayer of the plasma membranes of cells without the helpof membrane transport proteins; important in the movement of oxygen andcarbon dioxide between blood and body cells and between blood and airwithin the lungs during breathing.VI.facilitated diffusion – passive process wherein an integral membraneassists a specific substance across the membrane. The integral membranecan either be a membrane channel or a carrier.a.channel-mediated facilitated diffusion – solute moves down itsconcentration gradient across the lipid bilayer through membranechannel.i.ion channels – integral transmembrane proteins that allowpassage of small inorganic ions that are too hydrophilic topenetrate the non-polar interior of the lipid bilayer; mostmembranes are these.ii.gated channels – when part of the channel protein acts as aplug or gate changing the shape in one way to open the poreand in another way to close it; can be randomly alternatebetween open or closed positions; could be regulated bychemical or electrical changes inside and outside the cell.b.carrier-mediated facilitated diffusion – a carrier moves a solutedown its concentration gradient across the plasma membrane; nocellular energy is required in this passive process.
i.transport maximum – the upper limit on the plasmamembrane placed by the carriers at which the facilitateddiffusion can occur.