Why does active transport require energy to move molecules of a substance across a cell membrane?
a
The substance moves from low to high concentration, against the concentration gradient.
b
Lack of the substance makes the cell weak.
c
The substance moves from high to low concentration, with the concentration gradient.
d
The cell membrane is very thick.
a) The substance moves from low to high concentration, against the concentration gradient.
Active transport requires energy because it moves substances against their concentration gradient. This means that it moves substances from an area of lower concentration to an area of higher concentration. This process is energetically unfavorable and requires the input of energy to drive the transport.