Question

a scientist observes a cell actively expelling waste products against its concentration gradient, requiring the cell to use atp. which of the following statements best describes this process? a. this is an example of passive transport, as molecules are moving from an area of high concentration to low concentration. b. this process is diffusion, where water molecules move across a semipermeable membrane without energy expenditure. c. this illustrates facilitated diffusion, which uses protein channels but still follows the concentration gradient without atp. d. this is active transport, which utilizes energy from atp to move substances against their concentration gradient to maintain homeostasis.

Explanation:

Active transport moves substances against their concentration gradient using energy from ATP. The cell expelling waste products against the concentration gradient and using ATP is an example of this. Passive transport (A) moves from high - to low - concentration without ATP. Diffusion (B) is a type of passive transport and doesn't require energy. Facilitated diffusion (C) also follows the concentration gradient without using ATP.

Answer:

D. This is active transport, which utilizes energy from ATP to move substances against their concentration gradient to maintain homeostasis