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Cell Structure

The discovery of the cell as the basic common building block of all life was made as the result of the invention of the microscope. This happened in the 17th century, with developments being made to make the microscope more useful for science in Italy, Holland, and England.

Galileo and the compound microscope

Reports of visual enhancements being achieved by putting two lenses together date back to the 13th century. In the 1590s a compound microscope was already in use.

Bees
Bees by Francesco Stelluti, 1630, the earliest known image from microscope observations. The microscope is the Galilean design, the 'occhiolino'.

In 1609, Galileo Galilei presented his new telescope to an astonished world, and changed how humankind viewed its place in the universe forever. What is less well known is that Galilei also built an improved type of microscope.

In fact, the word microscope was first used by Giovanni Faber to describe the 'occhiolino' (little eye) instrument Galileo Galilei had built by 1625. We do not have any images made from observations of specimens under a microscope until 1630, when Francesco Stelluti drew closeups of bees.

Giambattista Odierna
Giambattista Odierna drew "L'occhio della mosca" (The Eye of the Fly) in 1644 from a Galilean compound microscope

Giambattista Odierna drew "L'occhio della mosca" (The Eye of the Fly) in 1644 using a microscope silimiar to the Galilean 'little eye'.

By the 1660s, the microscope was being used in England, Holland, and Italy, to investigate living things. One such pioneer was Marcelo Malpighi of Italy, who used the new instrument to unravel the secrets of organs like the lungs.

The compound Microscope

A compound microscope is a type of microscope and the most common type of optical microscope, which uses a set of lenses to produce an inverted virtual image of an object.

Compound microscope

The lens closest to the object being viewed focuses the light, to produce a real image inside the barrel of the microscope. the eyepiece is a second lens beyond the focal point of the objective lens, which magnifies the real image and creates the viewer's image, which is virtual.

For an explanation of real and virtual images from thin lenses see: Lenses

Hooke's discovery of the cell

Monk cell
Robert Hooke invented the name cell from comparing cork to monks' cells in a monastery!

In 1665, Robert Hooke of London published his ground-breaking Micrographia. This compendium of descriptions and beautifully detailed drawings of insects, plants and other biological structures instantly popularised the compound microscope and revealed its potential power to revolutionise scientific investigation.

Robert Hooke's microscope
Robert Hooke's microscope, used for his Micrographia drawings

Hooke invented the term 'cell'. When he examined a thin sliver of cork under this microscope, he discovered that it consisted of an orderly series of rows of what appeared to be empty boxes. They reminded him of monks' cells in a monastery. The name stuck.

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Robert Hooke's drawing of a flea, from his Micrographia

Antoine Van Leeuwenhoek

And in 1676, Antoine Van Leeuwenhoek turned his own version of the microscope, the spherical glass bead, on to the secret world of microorganisms in a droplet of pond water. Modern microbiology had begun.

Van Leeuwenhoek
Van Leeuwenhoek made improvements to the microscope, and was the first to observe microorganisms in water

Antonie van Leeuwenhoek was a Dutch draper who needed a better way to examine the tiny threads of cloth. His ingenious solution gave birth to the modern science of microbiology!

Van Leeuwenhoek experimented with lenses, and discovered that a perfect sphere of clear glass had a greater magnification than the magnifying lenses in use at the time. He developed the system and found it was powerful enough to reveal that pond water was the habitat for 'animalcules', his word for the unicellular amoeba and bacteria he found swimming around in a drop of water.

His microscopic investigations then extended to muscle fibre, unicellular organisms, bacteria, spermatozoa, and blood flow in capillaries. He reported his findings to the Royal Society in London in a series of letters, which they published.

The Cell

Cells are the basic units of life. Bacteria, plants and animals all have cells, and are responsible for growth, reproduction, energy and structure.

Onion cells
Onion inner epidermis, with cells revealed by dyeing

Despite the early progress in microscope technology, it was not until 150 years after van Leeuwenhoek's discovery, in 1838, that a German botanist, Matthias Schleiden, deduced that all plants consisted of cells. And then a fellow German, a biologist, Theodor Schwann, announced in 1839 that also animals consisted of cells.

This might sound like a logical conclusion, but in the mid-1880s the revelation that there was a fundamental connection between plants and animals, in both being made up of billions of cells, must have been a very exciting, and counter-intuitive, discovery. And this happened just as Charles Darwin was starting to formulate his theory of evolution.

Scientists now began to investigate these 'cells' in more detail. In 1855, a German doctor, Rudolf Virchow, found that cells were created by existing cells dividing. Biology now had a complete cell theory:

Cell Theory

  1. All living things are composed of cells
  2. Cells are the basic units of structure and function in living things
  3. New cells are produced by the division of existing cells

The word microscope is derived from Greek: micron (small) and skopein (to view or look at).

Content © Andrew Bone. All rights reserved. Created : August 21, 2015 Last updated :May 7, 2016

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