All living organisms are made up of cells. A cell is the basic structural and functional unit of life. Some organisms like bacteria and yeast have only one cell and are called unicellular, while plants, animals, and humans have many cells and are called multicellular. In multicellular organisms, similar cells form tissues, tissues form organs, and organs work together in organ systems. Yet, the cell remains the basic unit of structure and function in every living organism.
The chapter also connects the idea of cells to the origin of life. It explains that early protective membranes may have helped in the formation of the first cells. This shows why the cell boundary is so important in living systems.
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