• Cells were first observed in 1665 by Robert Hooke, who looked at thin slices of cork under a microscope
• He saw tiny roomlike structures
• He called them cells
• Several scientists worked together to develop the cell theory which states:
  • All living things are made of cells
  • Cells are the basic units of structure and function in all living things
  • Living cells come only from other living cells
• Cells grow and divide
• Because cells are so small, the microscope needed to be developed before scientists could study them