What is the correct order from largest structure to smallest within the lungs?
a. bronchi - trachea - bronchioles - alveoli
b. bronchioles - trachea - alveoli - bronchi
c. trachea - bronchi - bronchioles - alveoli
d. alveoli - bronchioles - bronchi - trachea

Lactase is essential for digesting lactose in milk. this enzyme is specific for this sugar. why? molecules and active sites vary in size; only properly sized molecules can fit. there is a precise compatibility between the active site and the lactose molecule. specificity refers to the action of the enzyme, such as hydrolysis, and relatively few molecules can be hydrolyzed. reaction-specific enzymes assume a fit by folding around the most numerous substrate molecules.