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
The substance moves from high to low concentration, with the concentration gradient.
c
The cell membrane is very thick.
d
Lack of the substance makes the cell weak.
a
The substance moves from low to high concentration, against the concentration gradient.
The correct answer is option a: The substance moves from low to high concentration, against the concentration gradient.
Active transport requires energy because it moves molecules or ions against their concentration gradient, from an area of low concentration to an area of high concentration. This process is in contrast to passive transport, which occurs down the concentration gradient. By actively transporting molecules against their concentration gradient, the cell can maintain or create concentration gradients that are essential for various cellular processes. The energy necessary for active transport is typically obtained from ATP, or adenosine triphosphate, which is generated through cellular respiration.