Partial pressure for oxygen and $CO_2$ is represented as

The partial pressure of oxygen in the alveoli of the lungs is

What is the thickness of the diffusion membrane involved in the exchange of gases in the lungs?

Which of the following factors affect the rate of diffusion?

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)

Water vapor exits from the leaves of terrestrial plants through open stomata. During photosynthesis,carbon dioxide enters the plant through the same open stomata. Identify the reason for the above statements from the following options.