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Correct Answer: A
Correct Answer: A
Method / Topic: Biology
The correct option matches the required rule and the given information.
Short Explanation
Detailed Explanation
Correct Answer: A
Method / Topic: Biology
The apical carrier couples downhill Na+ entry to uphill glucose uptake. The carrier does not hydrolyze ATP itself, so it is secondary active transport; the Na+/K+ ATPase indirectly supplies the energy by maintaining the Na+ gradient. For an MCAT biology problem, first identify the biological level being tested: molecule, cell, tissue, organ system, population, or experiment. Translate the stem into a cause-and-effect chain and use only the stated data plus a well-established biological principle. In physiology, follow the variable being regulated and decide whether the response is negative feedback. In genetics, separate parental from recombinant outcomes and show every probability step. In experiments, distinguish the manipulated variable, measured outcome, and appropriate comparison. Check units whenever a calculation is required. Then test every option against the mechanism; distractors often reverse direction, confuse correlation with causation, or name a true process occurring in the wrong cell, membrane, compartment, or stage. A final reasonableness check should confirm the
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PASSAGE 1 — INTESTINAL GLUCOSE TRANSPORT Researchers grow intestinal epithelial cells as a polarized sheet. Glucose enters across the apical membrane together with Na+ and exits across the basolateral membrane through a glucose carrier. A basolateral Na+/K+ ATPase maintains low intracellular Na+. Removing extracellular Na+ immediately reduces apical glucose uptake. Adding ouabain, an inhibitor of the Na+/K+ ATPase, reduces glucose uptake more gradually. The cells are joined near their apical surfaces by tight junctions. QUESTION 1: Which transport mechanism most directly moves glucose into these cells across the apical membrane?
Explanation
Correct Answer: A
Method / Topic: Biology
The correct option matches the required rule and the given information.
Short Explanation
Detailed Explanation
Correct Answer: A
Method / Topic: Biology
The apical carrier couples downhill Na+ entry to uphill glucose uptake. The carrier does not hydrolyze ATP itself, so it is secondary active transport; the Na+/K+ ATPase indirectly supplies the energy by maintaining the Na+ gradient. For an MCAT biology problem, first identify the biological level being tested: molecule, cell, tissue, organ system, population, or experiment. Translate the stem into a cause-and-effect chain and use only the stated data plus a well-established biological principle. In physiology, follow the variable being regulated and decide whether the response is negative feedback. In genetics, separate parental from recombinant outcomes and show every probability step. In experiments, distinguish the manipulated variable, measured outcome, and appropriate comparison. Check units whenever a calculation is required. Then test every option against the mechanism; distractors often reverse direction, confuse correlation with causation, or name a true process occurring in the wrong cell, membrane, compartment, or stage. A final reasonableness check should confirm the
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