If a group of cells is called a tissue, then what group is a cell made of? - Quora
Epithelium: What It Is, Function & Types
A Community of Cells How cells make up a body.. Cell Organization Cells are organized into systems that, together, perform functions that keep the organs. - ppt download
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Tissues, organs, & organ systems (article) | Khan Academy
Tissues, organs, & organ systems (article) | Khan Academy