Answer:
Active uptake (which I think you mean active transport) is important when the concentration gradient is against that of a certain substance, so it doesn't cross the membrane through diffusion or passive transport. It is sometimes necessary if a substance needs to move across a membrane but can't do so due to electrical charge or that there is a substance on the other side of the membrane preventing diffusion.
Explanation:
DNA can illustrate that evolution has occurred since in the process of natural selection advantegeous genes or traits have been selected to pass on through generations and further more evolve as long as the species survies and is successful in reproducing.