The sun, moon, and planets of the solar system are shown with their orbits.
the loops in ptolemy’s model, and those shown on the video, are called motion.

this phenomenon is caused by earth’s orbit than those of other planets.

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.