A Level Biology Practice Exam

Haemoglobinic acid is formed when haemoglobin:

1. Releases oxygen

2. Binds with free hydrogen ions

3. Absorbs carbon dioxide

4. Destroys pathogens

The correct answer is: Binds with free hydrogen ions

Haemoglobinic acid is indeed formed when haemoglobin binds with free hydrogen ions. This process occurs in the context of the transport of carbon dioxide in the blood. When haemoglobin picks up carbon dioxide, it tends to release oxygen, and during this process, it also increases the concentration of hydrogen ions in the blood. This shift in pH leads to the formation of haemoglobinic acid as hydrogen ions combine with deoxygenated haemoglobin. The other scenarios do not directly lead to the formation of haemoglobinic acid. While oxygen release and carbon dioxide absorption are processes associated with haemoglobin function, they do not involve the binding of hydrogen ions, which is crucial for the formation of haemoglobinic acid. Additionally, the destruction of pathogens is unrelated to the role of haemoglobin, which primarily focuses on gas transport and acid-base balance in the blood.