Name the substance whose build-up in the muscles during vigorous physical exercise may cause cramps.

Which of the following is not produced during anaerobic respiration in a unicellular fungus?

Which one of the following organisms does not depend on simple diffusion of gases for breathing and respiration?

Fill in the following blank with a suitable word:
$Gills$ are the breathing organs in . . . . . . .

What is the normal breathing rate in an adult human at rest?

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 $G$.