A cell is placed into a 1 millimolar solution of substance X and over time you witness the concentration of X inside the cell increase to 5 millimolar. What is the best explanation for this observation?
A) X is moving into the cell by simple diffusion.
B) X is moving into the cell by diffusion through a protein channel.
C) X is moving into the cell by facilitated diffusion.
D) X is moving into the cell by primary active transport.
E) Water is leaving the cell by osmosis.

Question

Quizplus · Accepted Answer

The concentration of substance X inside the cell has increased from 1 millimolar to 5 millimolar, which cannot be explained by simple diffusion or facilitated diffusion. This suggests an active transport mechanism, specifically primary active transport, which requires ATP to move molecules against their concentration gradient. Therefore, option D is the best explanation for this observation.

A Cell Is Placed into a 1 Millimolar Solution of Substance