a. moved against a concentration gradient/lower to higher concentration
b. energy/ATP required/used
c. pump/carrier «protein» «carries out active transport»
d. absorption «by active transport» into a cell is possible even if exterior concentrations are «very» low
OR
allows all/nearly all of/more of the substance/calcium to be absorbed «whereas diffusion can only even out concentrations»
OR
unidirectional/allows the direction of movement to be controlled
OR
allows a concentration gradient to be built up/potential energy to be stored/membrane potential to be generated/maintained
OR
allows a specific concentration to be maintained «in a cell»
3 max