How does the presence of CO2 in tissues affect hemoglobin's affinity for oxygen?

• A. It enhances affinity
• B. It maintains affinity
• C. It decreases affinity
• D. It has no effect

Answer: (C)

The presence of carbon dioxide (CO2) in tissues plays a crucial role in regulating hemoglobin's affinity for oxygen through a phenomenon known as the Bohr effect. When CO2 levels increase in tissues, it leads to a decrease in the pH of blood (making it more acidic). This acidic environment causes hemoglobin to change its shape, resulting in a lower affinity for oxygen.

As tissues metabolize and produce CO2, they create a need for more oxygen that can be delivered more readily when hemoglobin's affinity decreases. This allows for efficient oxygen unloading in areas where it is most needed—such as active tissues that are producing CO2 and consuming oxygen at high rates. Therefore, the correct choice indicates that the presence of CO2 indeed decreases hemoglobin’s affinity for oxygen, facilitating the release of oxygen into those metabolically active tissues.