In the human circulatory system, arteries carry blood away from the heart to different parts of the body. Veins carry blood from different parts of the body back to the heart. A scientist claims that the greater the amount of exercise a person performs, the greater the amount of oxygen (O2) the body uses. He records the oxygen concentration in the blood of people while they are riding an exercise bike. The graphs show the results of this investigation. a. Identify at least two systems within the human body that work together during exercise.

b. Explain how the evidence from the data in the graphs supports or does not support the scientist’s claim.