Under normal physiological conditions,$100 \, mL$ of oxygenated blood delivers how much $CO_2$ to the alveoli?

In the given diagram representing the partial pressure of gases in the systemic circulation,what are the partial pressures of $CO_2$ at $P$ and $Q$ respectively? (Assuming $P$ is deoxygenated blood entering the lungs and $Q$ is oxygenated blood leaving the lungs)

Which structure of the lungs is directly involved in $O_2 / CO_2$ exchange between air and blood capillary?

Identify the correct option for the diffusion membrane.

Diffusion of gases occurs in the alveolar region only and not in the other parts of the respiratory system. Why?

The blood leaving the lungs has all its haemoglobin oxygenated. Why does it give up oxygen to the tissues?