A Level Biology Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The Bohr effect describes how an increase in carbon dioxide concentration leads to a decrease in hemoglobin's affinity for oxygen. This physiological phenomenon is crucial for optimizing oxygen delivery to tissues that are metabolically active and producing more carbon dioxide, such as during exercise or in areas of high cellular respiration. The presence of carbon dioxide lowers the pH of the blood, which results in conformational changes in the hemoglobin molecule, promoting the release of oxygen.

This mechanism ensures that the tissues that need oxygen the most, which typically generate more carbon dioxide, receive it efficiently. Other options do not pertain to the direct relationship between carbon dioxide levels and hemoglobin's oxygen binding capacity. For instance, the choking effect deals with airway obstruction, Dalton's law relates to the behavior of gases in mixtures, and oxyhemoglobin dissociation describes the process of hemoglobin releasing oxygen but does not specifically address the influence of carbon dioxide concentration. The Bohr effect thus uniquely captures this critical interaction in oxygen transport physiology.