A Level Biology Practice Exam 2025 – All-in-One Study Guide to Excel in Your A Levels!

The increased release of oxygen from oxyhaemoglobin in active tissues is primarily influenced by the physiological mechanism known as the Bohr effect. When tissues engage in higher levels of metabolic activity, they consume more oxygen and produce more carbon dioxide as a byproduct of respiration.

As carbon dioxide levels rise, they contribute to a decrease in blood pH (increased acidity), which causes a conformational change in the structure of hemoglobin. This change reduces the affinity of hemoglobin for oxygen, promoting the release of oxygen where it is needed most—in actively metabolizing tissues. Additionally, the presence of carbon dioxide helps in binding protons (H+ ions), further enhancing this oxygen release.

In contrast, factors like decreased temperature or increased affinity would promote the retention of oxygen rather than its release. Higher concentrations of nitrogen do not directly influence hemoglobin's oxygen-carrying capacity or its ability to release oxygen. Thus, increased carbon dioxide concentration directly facilitates oxygen release in active tissues, making it the correct mechanism in this context.