Cell Membrane In 1665, Robert Hooke, an English scientist observed cork under a microscope and noted that it was composed of small units. He called these units cells. Later it was observed that most living things are composed of cells. This led to cell theory. Cell theory is that living things are composed of cells. A theory is a hypothesis that scientific investigations have shown to be true most of the time. A law is a …showed first 75 words of 1164 total…

…showed last 75 words of 1164 total…a solid particle is taken in through endocytosis, this process is referred to as being phagocytosis, a word which means "cell eating." It is through phagocytosis that white blood cells eat bacteria. If a liquid is taken in through endocytosis, this process is called pinocytosis, a word which means "cell drinking." A reverse process is used to rid cells of wastes or to expel useful substances needed elsewhere. This process is called exocytosis (cell exiting).