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Q13 - Renal Handling of Glucose

Theoretical A Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license
Human Excretory System

The following graph shows how glucose handling in the kidney changes with plasma concentration.

Graph with x-axis plasma glucose concentration (mg/100ml) from 0-800, y-axis glucose filtered load/reabsorption/excretion (mg/min) from 0-900. Curve A is a straight diagonal line from the origin, rising steepest of all four and reaching ~870 at x=800. Curve B starts flat at zero, curves upward starting around x=250, and rises roughly parallel to A but offset below it. Curve C rises from zero in a shallow S-curve and plateaus at y≈400 from about x=400 onward. A small bracket labeled D marks a specific x-axis position around x=100-180. Fig.1. Axis 1 = Plasma glucose concentration (mg/100 ml). Axis 2 = Glucose filtered load, reabsorption or excretion (mg/min).

Match the letters from the figure (A-D) to the correct parameter in the list below.

Q13.1. Glucose is freely filtered in glomeruli.
Q13.2. The graph plots glucose filtered load, reabsorption, and excretion (mg/min) against plasma glucose concentration as curves A-D. Which curve is glucose EXCRETED?
Q13.3. Which curve is glucose FILTERED?
Q13.4. Which curve is glucose REABSORBED?
Q13.5. Which marking indicates "normal levels" (a reference point for normal fasting plasma glucose)?
Q13.6. What is the maximum rate of glucose reuptake (the transport maximum, Tm)? Round to the nearest hundred, in mg/min.
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Question reproduced from IBO 2019, Theoretical Exam A, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Official answer key