Question 1
Multiple choiceEasy1 markSolutes X and Y each have lower concentrations outside a cell than inside. Membrane protein P transports X into the cell, but not Y; this movement stops when ATP is unavailable. Which description best explains P’s action?
Show answer and explanation
Answer: D. The concentration of X is lower outside the cell, so inward movement is against its concentration gradient. P transports X but not Y, showing selectivity, and its activity depends on ATP. It therefore acts as a selective pump using ATP for active transport.
A: Confuses active transport with facilitated diffusion, which does not use ATP to move particles against a concentration gradient.
B: Reverses the observed direction of X transport.
C: Treats P as non-selective, although it transports X but not Y.
Remember: pumps use ATP to move specific particles against concentration gradients.