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The first microscope

What he did: Adapted his telescope design to make one of the earliest microscopes.

What it was like: Used a bi-convex objective lens and a bi-concave eyepiece, similar to his telescope.

Magnification: About 30x.

Name of device: He called it the “occhiolino” (Italian for “little eye”).

Why it matters: While Galileo didn’t invent the microscope or use it for biology much, his work laid groundwork for magnification tools.

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1665 – Robert Hooke

What he did: Observed thin slices of cork using a compound microscope.

Discovery: He saw many tiny, box-shaped structures.

What he called them: “Cells”, because they reminded him of monks’ small rooms (cellulae).

Impact: First person to name and describe cells, even though he only saw the cell walls of dead plant cells.

Why it matters: This was the first step toward understanding that all living things are made of cells.

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1670 – Antonie van Leeuwenhoek

What he did: Built simple, single-lens microscopes with powerful magnification (up to 270x).

How: Used tiny, hand-polished glass beads as lenses.

Discoveries: First to see and describe living microorganisms, including:

Bacteria

Sperm cells

Protozoa

Blood cells

Nickname: The “Father of Microbiology”.

Why it matters: He showed that an entire invisible world of life exists, launching the study of microbiology.

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What he did: Studied plant cells under a microscope.

Discovery: Observed a dark structure in orchid cells and named it the nucleus.

Why it matters: The nucleus was later found to be the control center of the cell, making this a key discovery in cell biology.

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Focus: Studied plants and their structure.

Conclusion: All parts of a plant are made of cells.

Partnered with: Theodor Schwann (who studied animals).

Why it matters: Together, Schleiden and Schwann helped create the foundation of the Cell Theory:

All living things are made of cells.

Cells are the basic unit of life.

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What he did: Revised and expanded the Cell Theory.

New idea: Cells are not just structural, but also the functional units of life—meaning they carry out all the basic activities of living things.

Why it matters: Helped clarify that cells aren’t just building blocks—they actually do the work of life.

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What he said: “Omnis cellula e cellula” — All cells come from pre-existing cells.

Why it was important:

Went against the old idea of spontaneous generation (that life could come from non-living things).

Showed that cells divide to make new cells.

Helped prove that diseases start at the cellular level, leading to modern pathology.

Why it matters: Completed the modern Cell Theory.