Protoplasm, living matter. It is generally colorless, nearly transparent, and slightly heavier than water. The consistency of protoplasm varies from watery to jellylike; usually it is viscous and can be drawn out in threads, like the albumen of an egg. Protoplasm typically is organized into microscopic structures called cells.

The chemical composition of protoplasm is very complex. Carbon, hydrogen, oxygen, and nitrogen are main elements. Biologists once assumed that protoplasm is everywhere the same. Since then biochemists and biophysicists have discovered and named many kinds of protoplasmic material in various types of cells and parts of cells. The term protoplasm therefore is too broad and indefinite to have scientific meaning, and is little used by researchers.