Exchange of gases in man takes place at the level of

Which of the following is correct regarding the partial pressures of gases ($PO_2$ and $PCO_2$) in different parts of the human respiratory system?

In humans,exchange of gases occurs

The diffusion membrane of the lungs,through which the exchange of gases occurs,is made up of which of the following layers?

The solubility of $CO_2$ is ....... times higher than that of $O_2$.

Explain: Diffusion of $O_2$ from alveoli to tissues and of $CO_2$ from tissues to alveoli.