is an on-going process. It can be done at any stage of the process. The behavior of the participants is observed and is critical to the analysis of results. Analysis of data is less time-consuming.
air enters your lungs, and oxygen from that air moves to your blood. At the same time, carbon dioxide, a waste gas, moves from your blood to the lungs and is exhaled (breathed out). This process, called gas exchange, is essential to life.