Membrane transport mechanisms: diffusion through the cell membrane. Substance must be nonpolar/lipid soluble (oxygen, carbon dioxides, large alcohols) Must be able to get through the inner portion of the bilayer. Fick"s first law of diffusion predicts rate: Negative sign because the concentration gradient produces a negative slope, so we need the negative sign to make the rate of diffusion positive. Rate is proportional to: area for diffusion, temperature, concentration gradient. Inverse of the viscosity of the medium: diffusion through protein channels/pores. Molecules passing through the channels don"t physically interact with them: facilitated diffusion. Large molecules (i. e. glucose) use facilitated diffusion. Conformational change in protein, which moves the molecule across the membrane. Form of carrier-mediated transport, but driving force is still the concentration gradient. Form of carrier mediated transport: chemical specificity, competitively inhibited, shows saturation kinetics. Moves substances against concentration gradient, which requires energy (i. e. atp) Pumps 3 na out & 2 k in for every atp.