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Chapter 1 introduced some of the characteristics of life: chemical complexity, growth and reproduction, the ability to refashion substances from the environment, and the ability to move specific substances into and out of the organism. Cells have all of these characteristics. Just as atoms are the building blocks of chemistry, cells are the building blocks of life.
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Cell theory states that the cell is the smallest unit of life, that cells make up all living organisms, and that cells come from existing cells.
Microscopy allows visual examination of cells.
Membranes provide a structural role in a cell and also allow the cell to maintain homeostasis and communicate with other cells.