peristalsis: The action of food being moved down the esophagus and through the entire digestive tract.

peroxisomes: Sacs of enzymes within animal cells that help protect the cell by breaking down accumulations of toxic products such as hydrogen peroxide.

photosynthesis: The biochemical process that plants use to acquire energy from the sun.

plasma membrane: The membrane that holds fluid within animal cells. Also called the cell membrane.

polysaccharides: Carbohydrate molecules that are formed by many long chains of monosaccharides.

prokaryotes: Organisms — such as bacteria and blue-green algae — with cells that do not contain a nucleus.