The most numerous cells in the epithelium of the bronchus and bronchioles are called:

The branchioles end in millions of tiny interconnected cavities called:

Which one of the following is the by-product gas of photosynthesising ?

The water proof layer that protects human skin.

In large organisms, such as humans, the ratio of surface area to volume is:

Gases are diffused in and out of leaves through small openings called stomata. A stomata is surrounded by two cells called:

Fish gills are covered by a bony flap called:

Carbon dioxide and oxygen diffuse in and out of leaves through small openings called:

Guard cells become turgid by actively transporting which of the following ions?

Write the name of the process of stomatal opening and closure.