Answer:
B. active transport using ATP
Explanation:
In order to move the molecules across the cell membrane against the concentration gradient energy is required. ATP is most abundant energy resource used to start chemical processes in biological systems. There is membrane transport proteins which need ATP for activation. Active transport of molecules can be classified in to two groups. Primary active transport which require energy like ATP. Secondary active transport involves the use of an electrochemical gradient, and does not use energy produced in the cell.
