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← Theoretical A

Q4 — Tumor Microenvironment: OCR and Extracellular pH

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license
Bioenergetics & Central Metabolism Overview

The extracellular pH of normal tissues is typically between 7.35 and 7.45. Meanwhile, in the tumor microenvironment, extracellular pH is mildly acidic in the range of 6.5–6.9. Figure 1B provides an overview of the average extracellular pH values observed in different tumor types compared to their respective normal cells. Cancer cells also exhibit changes in the oxygen consumption rates (OCR). This phenomenon is demonstrated in Figure 1A by comparing the OCR of normal and cancer cells from three patients.

Panel A: bar chart of single-cell oxygen consumption rate for normal (green) vs. cancer (blue) cells from three patients, with cancer cells higher in each case and Patient 2’s cancer cells showing the widest spread. Panel B: dot plot of extracellular pH for tumor tissue (blue) vs. normal tissue (black) across skin, vulvar, uterus, lung, breast, brain, and muscle, with tumor tissue consistently more acidic. Figure 1. A Oxygen consumption rates (OCR) in arbitrary units (AU) of normal and cancer cells. B Extracellular pH of normal tissue and corresponding tumor tissue. Asterisk indicates a significant difference.

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Difference in oxygen consumption between cancerous and normal cells indicates that tumor cells exhibit decreased metabolic rate.
B. Differences in extracellular pH values can be explained by the altered ratio of glucose fermentation to oxidative phosphorylation in cancer cells compared to normal ones.
C. The tumor microenvironment is typically hyperoxic due to elevated oxygen consumption by cancer cells.
D. The cancer cells of patient 3 are more heterogeneous compared to the cancer cells of the other two patients.
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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)