This document provides an overview of cells, their history and components. It discusses that cells are the basic unit of life, and can be single-celled or multi-celled. It describes the key parts of animal and plant cells including the cell membrane, nucleus, mitochondria and chloroplasts. It also discusses different cell types, tissues, organs and organ systems and how cells are organized in living things. Microscopes are introduced as a tool to study cells. Viruses are defined as needing a host cell to survive and able to infect all living things.
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