This is the sub topic of Respiratory System of Human. This includes in class 11th NCERT book. This class is helpful for the students who's preparing for NEET and class 11th students can also learn from this class. In this class we learn about how the gases exchange inside the body of human. This class includs how the gases passes through from the atmosphere to the lungs even alveoli. Alveoli is the functional unit of lungs in which exchange of gases takes place. For the exchange their a pressure works that is called partial pressure(pp), this is differ for different gases. In this class we learn about oxygen and carbon dioxide partial pressure. And air passes through High pressure to low pressure therefore exchange of oxygen in alveoli the pressure of oxygen is high in alveoli and low in blood capillary so oxygen moves from alveoli to the blood capillary and carbon dioxide moves simultaneously.