17. Protein pumps actively transport molecules (and especially
ions) across plasma membranes. This process often involves moving molecules
or ions from lower concentrations to higher concentrations.
Such a process involves the input of energy in order to function.
ATP is a small energy molecule all cells use as short term energy storage molecules.
The ATP gives a small measured dose of energy to the protein pump which then
is able to "pump" the required particles across the membrane.
[----------------
Slichter