Question

the table shows the concentrations of substances inside and outside of the cell and the direction the substances move over time.

substance	concentration inside the cell	concentration outside the cell	direction of movement
molecule 2	high	low	out of cell
molecule 3	low	high	out of cell
molecule 4	high	low	into cell

which two molecules cross the cell membrane by active transport?
molecules 2 and 3
molecules 1 and 2
molecules 1 and 4
molecules 3 and 4

Explanation:

Active transport moves substances against their concentration gradient (from low - concentration to high - concentration). Molecule 1 moves from low concentration outside to high concentration inside, and Molecule 4 moves from low concentration outside to high concentration inside. Molecule 2 and Molecule 3 move down their concentration gradients (from high to low), which is passive transport.

Answer:

C. Molecules 1 and 4