Cytology is the study of cells. Key developments include Anton van Leeuwenhoek discovering microorganisms in the 1670s, Robert Hooke coining the term "cell" in 1665, and Rudolph Virchow establishing that all cells come from pre-existing cells in 1855. The document then describes the basic components of plant and animal cells, including the cell membrane, nucleus, cytoplasm, organelles, and differences between prokaryotic and eukaryotic cells.