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Zacharias Janssen invented the microscope in 1590. It consisted of two lenses mounted inside a tube. His invention allowed other scientists to discover things about the cell.

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English scientist Robert Hooke used a compound microscope to observe thin slices of cork. He noticed small box-like structures, which he called 'cells' because they reminded him of monks' cells in a monastery. This was the first time the term 'cell' was used in biology.

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Anton van Leeuwenhoek made significant improvements to the microscope. He was the first to observe and describe single-celled organisms, which he called 'animalcules'. His work with bacteria, sperm cells, and blood cells greatly advanced the study of microbiology.

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These cells were the ones that Anton Van Leeuwenhoek saw

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German botanist Matthias Schleiden concluded that all plant tissues are composed of cells. He proposed that the cell is the basic unit of plant structure, a crucial step towards the development of cell theory.

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Vegetables cells

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Theodor Schwann extended Schleiden's work to animal tissues. He concluded that all animal tissues are also composed of cells, unifying the understanding of plant and animal structures.

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Rudolph Virchrow discovered that come from pre-existing cells. His famous quote 'Omnis cellula e cellula' (All cells come from pre-existing cells). This completed the classical cell theory by explaining how cells reproduce and where new cells come from became a fundamental principle in biology.

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Since the formation of classical cell theory, further studies on cells with the advancement of microscope have led to the formation of the modern cell theory, which has three main additions:

1. Genetic material (DNA) is passed on from one cell to another during cell division

2. All cells have the same basic chemical composition

3. Energy flow occurs within cells

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What are the characteristics that make something “alive”?

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What are the characteristics that make something “alive”?

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From a single organelle to the entire biosphere, living organisms are parts of a highly structured hierarchy.