Why does active transport require energy to move molecules of a substance across a cell membrane?
A.
Lack of the substance makes the cell weak.
B.
The substance moves from low to high concentration, against the concentration gradient.
C.
The cell membrane is very thick.
D.
The substance moves from high to low concentration, with the concentration gradient.
B. The substance moves from low to high concentration, against the concentration gradient.
B. The substance moves from low to high concentration, against the concentration gradient.
The correct answer is B. The substance moves from low to high concentration, against the concentration gradient.
Explanation:
Active transport is a process in which molecules or ions are moved across a cell membrane against their concentration gradient, from an area of low concentration to an area of high concentration. This movement requires the cell to expend energy in the form of ATP (adenosine triphosphate).
Unlike passive transport, such as diffusion or facilitated diffusion, which move substances down their concentration gradient, active transport goes against the concentration gradient. This is because active transport allows cells to accumulate substances at higher concentrations than what is found in the surrounding environment.
To accomplish this, transport proteins embedded in the cell membrane called pumps are utilized. These pumps use ATP energy to pump molecules or ions across the membrane. By doing so, they create and maintain concentration gradients that are essential for many cellular processes, such as nerve cell signaling, nutrient uptake, and waste removal.
In summary, 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.