The expert answered my question 1, 2 and 3. Please answer the last two as well:
Please find below the answer:
4. Residual volume is the amount of gas remaining in the lungs at the end of a maximal exhalation. Residual Volume is important because it prevents the lungs from collapsing. Even after we have expelled as much air as possible (expiratory reserve volume) gaseous exchange is still occurring by residual volume in the lungs. It also prevents the inner surfaces of the lungs from sticking together.
The lungs always contain a residual volume of air so that during the breathing cycle there is sufficient time for oxygen to be absorbed and for the carbon dioxide to be released.
5. The exchange of gases takes place between the blood of the capillaries that surround the alveoli and the gases present in the alveoli. Thus, alveoli are the site for the exchange of gases. The lungs get filled up with air during the process of inhalation as ribs are lifted up and the diaphragm is flattened. The air that is rushed inside the lungs fills the numerous alveoli present in the lungs.
Each lung contains 300-350 million alveoli. These numerous alveoli increase the surface area for gaseous exchange making the process of respiration more efficient.
Hope this clears your doubt.Regards.