Partial pressure of a gas is the pressure contributed by

Analogy type question:
$(1)$ Atmospheric air enters: Inspiration :: Alveolar air released out: ..........
$(2)$ $O_2$ in alveoli: $104 \, mm \, Hg$ :: $CO_2$ in alveoli: ..........

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

The low partial pressure of oxygen $(PO_2)$ in the body cells results in:

Which of the following factors is most necessary for an efficient respiratory surface?

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.