The normal rate of breathing in a healthy human adult is:

Select the correct statements from the following regarding gaseous exchange in plants.
$A$. $A$ terrestrial plant has many air spaces between the cells of leaf and root.
$B$. Woody trees have stomata on bark.
$C$. In aerated soil,oxygen dissolved in water enters root tissue by diffusion.
$D$. Vascular bundles provide thin and large surface area for exchange of gases.
$E$. Carbon dioxide and water vapour diffuse into lenticels.

Which of the following structures is lined by guard cells?

Breathing differs from respiration by

Vitamin $D$ is synthesized by one of the following with the help of sunlight.

Define breathing.