Goblet cells in the trachea secrete mucus.

Autotrophs can synthesize organic matter from inorganic matter.

What is the main purpose of villi and microvilli in the small intestine?

Which type of bone contains marrow?

The process of breathing (inhaling and exahaling) is called:

                   make up the greatest proportion of the biomass in nearly all ecosystems.

Which innate immune cell produces histamines?

Where do T cells (lymphocytes) mature? 

Where in the lungs does gas exchange occur with the blood vessels?

Which structure of the respiratory system contains the vocal cords (sometimes called vocal folds)?