The Bohr effect describes the phenomenon where:

 # The Bohr effect describes the phenomenon where:

 A. An increase in CO₂ and H⁺ ions causes hemoglobin to release oxygen more readily.

 B. A decrease in temperature increases hemoglobin's affinity for oxygen.

 C. An increase in O₂ causes hemoglobin to release CO₂ more readily.

 D. An increase in CO₂ causes hemoglobin to bind more oxygen.

The correct answer is A. An increase in CO₂ and H⁺ ions causes hemoglobin to release oxygen more readily.

The Bohr effect describes how hemoglobin's affinity for oxygen decreases in conditions of increased carbon dioxide (CO₂) and hydrogen ion (H⁺) concentration (i.e., lower pH). This occurs in metabolically active tissues, where higher CO₂ and H⁺ levels promote oxygen release from hemoglobin to meet the tissue's oxygen demands. The effect enhances oxygen delivery where it is needed most.

• B. A decrease in temperature increases hemoglobin's affinity for oxygen: While temperature affects hemoglobin's oxygen affinity (lower temperatures increase affinity), this is not the Bohr effect, which specifically involves CO₂ and H⁺.
• C. An increase in O₂ causes hemoglobin to release CO₂ more readily: This describes the Haldane effect, not the Bohr effect.
• D. An increase in CO₂ causes hemoglobin to bind more oxygen: Incorrect, as increased CO₂ reduces hemoglobin's oxygen affinity, promoting oxygen release, not binding.