Click within the box to reset all the particles to a single point. For a more extensive review of Diffusion, Osmosis, and Nernst Potentials, see my separate chapter on that subject. Facilitated Diffusion Proteins act as carriers or pores permit flux of substances that cannot diffuse directly through the membrane. Occurs across cell membranes only. Saturates when substance reaches high concentrations due to lack of available protein.
Related substances can compete for the same carrier or pore.
Primary Active Transport Proteins in the membrane can also act as pumps. Require cellular energy, usually as ATP Saturates when substance reaches high concentrations due to lack of available protein. Secondary Active Transport Uses proteins similar to those for facilitated diffusion. Couples the movement of several different molecules in each cycle. Saturates when substance reaches high concentrations due to lack of available protein.