Final answer:
The absorption of glucose from the gut lumen depends on the sodium-potassium pump, symport cotransporter proteins, and the higher sodium ion concentration in the lumen than in the epithelial cell. All mechanisms contribute to the active transport and facilitated diffusion required for glucose uptake.
Step-by-step explanation:
The absorption of glucose from the gut lumen depends on several factors, including symport mechanisms and active transport processes. Glucose and sodium ions bind to the same cotransporter proteins on the apical surface of the epithelial cell layer, allowing their simultaneous transport into the cell. Once inside, glucose moves towards the interstitial space by facilitated diffusion, whereas sodium ions are actively pumped out across the basal side via the sodium-potassium pump (Na+/K+ ATPase), which requires ATP to function.
This arrangement establishes an electrochemical gradient that is necessary for the absorptive processes. Thus, the active transport of glucose against its concentration gradient is fundamentally linked to the electrochemical gradient created by the sodium-potassium pump. To answer the student's question: all of the provided answers are correct in explaining the dependence of glucose absorption from the gut lumen.