Question

Active transport performs which function in a cell?

Answer 1

Answer:

Moves substances against a concentration gradient.(Ans. C)

Explanation:

Active transport is defined as movements of molecules against a concentration gradient across a membrane from lower concentration to higher concentration, which requires the cell energy harvested from the ATP which is obtained from cellular metabolism.

Such metal ions include Mg+, K+, Ca+, Na+ these are transported across the cell membrane via active transport. These metal ions cross the cell membrane with the help of ion channels and pumps.

Primary active transport uses adenosine triphosphate and secondary active transport uses electrochemical gradient as an energy source.

Answer 2

Its C, as in active transport the substance tends to move from a reigon of high concentration to a reigon of lower concentration, against the concentration gradient. for example: mineral salts from soil move by active transport to the root hair cell.
D is not the answer as water always moves by the process of osmosis. 
i hope that helped (: