Question

which of the following accurately describes an example of how materials can move across the cell membrane through active transport?
○ a a protein acts as a channel to allow large, hydrophilic molecules to diffuse across the cell membrane.
○ b a protein acts as a pump and moves calcium ions from an area of low - concentration to an area of high concentration.
○ c the cell membrane folds to surround a substance and bring the substance inside the cell during endocytosis.
○ d water moves by osmosis from higher concentration to lower concentration by passing through protein - lined aquaporins.

Explanation:

Active transport requires energy and moves substances against their concentration gradient. Option b describes a protein acting as a pump moving calcium ions from low to high concentration, which is an example of active transport. Option a is passive - facilitated diffusion, option c is endocytosis, and option d is osmosis (a form of passive transport).

Answer:

B. A protein acts as a pump and moves calcium ions from an area of low concentration to an area of high concentration.