USA Biology Olympiad (USABO) Practice Exam

In plant cells grown in the presence of a metabolic poison that inhibits mitochondrial F1ATP synthase, what alteration is expected?

1. The overall pH difference across the cristae will change

2. The production of ATP will be unaffected

3. The number of mitochondria will increase

4. The plant will show enhanced photosynthesis

The correct answer is: The overall pH difference across the cristae will change

In the scenario described, where plant cells are exposed to a metabolic poison that inhibits mitochondrial F1ATP synthase, the most significant alteration expected is a change in the overall pH difference across the cristae of the mitochondria. F1ATP synthase is crucial for synthesizing ATP, utilizing the proton gradient established by the electron transport chain. When this enzyme is inhibited, ATP production is drastically affected because protons can no longer flow back into the mitochondrial matrix through the ATP synthase complex. This inhibition results in a disruption of normal proton movement, which alters the proton gradient and thus modifies the pH across the cristae membranes. The increased accumulation of protons in the intermembrane space (due to lack of usage by ATP synthase) would lead to a lower pH compared to the matrix, ultimately causing an overall change in the pH difference that is fundamental for cellular respiration processes. In contrast, ATP production would indeed be significantly impaired, making it incorrect to expect it to remain unaffected. The demand for ATP is critical, and in the presence of the poison, the plant cells would struggle to generate sufficient energy. The number of mitochondria in the cells may not necessarily increase as a direct response to the inhibition of ATP synth