Q55 — X-Irradiation of Yeast — NAD(P)H Fluorescence and Metabolic Recovery

Theoretical 2 Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

Bioenergetics & Central Metabolism Overview

The metabolic activity of equal-sized cultures of yeast was explored under 3 conditions: non-irradiated, X-irradiated and recovered (during 24-hour post-irradiation incubation), determined as the relative increase in NADPH fluorescence intensity (FI) during forced aerobic-anaerobic (AA) transition, using the equation ΔFI = (FI_AN - FI_AE) × 100, where FI_AN and FI_AE represent the FI under anaerobic and aerobic conditions respectively.

Figure. Fluorescence intensity curves of NADPH during the aerobic-anaerobic transition for non-irradiated, X-irradiated, and recovered yeast cells. AS = air sparging, NS = nitrogen sparging. Figure. NADPH fluorescence intensity during the aerobic-anaerobic transition, compared across the three conditions.

Using the figure and data above, determine whether the following statements are true or false.

A. The metabolic activity of yeast cells was disrupted under the influence of X-radiation, i.e. the metabolism of yeast cells stopped, and they all died.

B. Metabolic processes in yeast changed under the influence of X-radiation, and, as a result, the fluorescent properties of intracellular NADP(H) were altered due to the structural damage of NADPH.

C. During the post-irradiation incubation period, due to the repair processes in yeast cells, their metabolism was recovered, and they began to function like native yeasts.

D. The weak fluorescence intensity of intracellular NADPH of X-irradiated yeasts is associated with a decrease in the amount of NADPH due to a severe decrease in metabolism.

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Question reproduced from IBO 2022, Theoretical Paper 2, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)