A Level Biology Practice Exam

What does partial pressure measure concerning oxygen?

1. The total pressure of all gases

2. The volume of oxygen in a given space

3. The concentration of oxygen in a gas mixture

4. The temperature effects on gas law

The correct answer is: The concentration of oxygen in a gas mixture

The correct answer focuses on the concept of partial pressure as it relates specifically to oxygen within a mixture of gases. Partial pressure measures the concentration of a specific gas, in this case, oxygen, in a gas mixture. It is defined as the pressure that the gas would exert if it occupied the entire volume by itself, at the same temperature. Understanding this helps in various contexts, such as respiratory physiology, where the partial pressure of oxygen plays a crucial role in gas exchange in the lungs and the transportation of oxygen in the bloodstream. It reflects how much oxygen is available for diffusion into tissues and how it impacts biological processes. The other options address different aspects of gas behavior or measurements but do not accurately describe the relevance of partial pressure in this context. For instance, measuring the total pressure of all gases does not isolate oxygen’s contribution, while volume pertains to the space occupied without indicating concentration. Temperature effects relate to gas laws but do not define partial pressure directly. Therefore, the focus on the concentration of oxygen is what makes this choice the correct interpretation of partial pressure in the context of a gas mixture.