Mechanisms of Transport Practice Test

A drug blocks a specific membrane carrier. After treatment, a polar nutrient no longer enters cells, even though extracellular nutrient concentration remains higher than intracellular. ATP levels in the cell are unchanged. When the drug is removed, nutrient entry resumes and stops at equilibrium. Which mechanism best explains nutrient entry when the carrier is not blocked?

A transporter binds glucose on the extracellular side and releases it into the cytosol. Extracellular glucose is 1 mM and cytosolic glucose is 10 mM, yet glucose still enters the cell. The transport rate decreases sharply when ATP is depleted and resumes when ATP is restored. Blocking Na$^+$ gradients has no effect. Which mechanism best explains glucose entry in this experiment?