How are inspiration and expiration brought about in human beings?

When a person breathes in air, the air enters into his body through an organ $A$ having two holes $B$ in it. The air then passes through pharynx and larynx and enters into a tube $C$. The tube $C$ divides into two smaller tubes $D$ at its lower end. The two smaller tubes are attached to two respiratory organs $E$. Each smaller tube divides inside the organs $E$ to form a large number of still smaller tubes called $F$. The smallest tubes $F$ have air-sacs $G$ at their ends in which gaseous exchange takes place in the body of the person. Identify $A, B, C, D, E, F$ and $G$.

Assertion $(A)$: In the daytime, $CO_2$ generated during respiration is used up for photosynthesis.
Reason $(R)$: There is no $CO_2$ release during the day.

Explain the process of breakdown of glucose in a cell: $(i)$ In the presence of oxygen. (ii) In the absence of oxygen.

Where in the lungs does gas exchange take place?

In human beings, where does the gaseous exchange take place?