What changes occur to your breathing and heart rate during exercise? Why do you think these changes occur?

Your breathing increases, because your body is demanding more oxygen for delivering the right of amount of blood (flow) to the muscles, as well as the heart.

When your body exerts itself more than it's normal state, your muscles want more oxygen for the creation of ATP.

Your breathing will become more shallow and heart rate will increase. This is the bodies response to physical exertion in order for the body to be oxygenated faster.