American Society for Clinical Pathology (ASCP) Technologist in Cytogenetics certification (ASCP CG) Practice Test

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A change of 1 pH unit in culture medium is caused by what change in CO2 concentration?

5-fold change
2-fold change
10-fold change
20-fold change

The correct answer is: 10-fold change

The relationship between pH and carbon dioxide (CO2) concentration is governed by the bicarbonate buffer system in biological systems. When CO2 levels increase, it reacts with water to form carbonic acid, which dissociates into bicarbonate and hydrogen ions, ultimately lowering the pH. Conversely, a decrease in CO2 leads to fewer hydrogen ions and an increase in pH. The change in pH is logarithmic; specifically, a change of 1 pH unit corresponds to a 10-fold change in hydrogen ion concentration. Since CO2 concentration directly influences hydrogen ion concentration, a change of 1 pH unit reflects a 10-fold change in CO2 concentration as well. Therefore, the choice indicating a 10-fold change corresponds directly to the established biochemical principle involving pH and CO2 levels, making it the correct answer.