Some cells are visible to the human eye. The smallest objects that the unaided human eye can see are about 0.1 mm long. That means that under the right conditions, you might be able to see an ameoba proteus, a human egg, and a paramecium without using magnification. A magnifying glass can help you to see them more clearly, but they will still look tiny. Smaller cells are easily visible under a light microscope. It's even possible to make out structures within the cell. Light microscopes use a system of lenses to magnify an image. The most powerful light microscopes can resolve (form images of) bacteria but not viruses. To see anything smaller than 500 nm, you will need an electron microscope. The most powerful electron microscopes can resolve (form images of) molecules and even individual atoms. From: http://learn.genetics.utah.edu/content/begin/cells/scale/
12 s061101 c_meet the scientists
MEET THE SCIENTISTS
DEVELOPING THE CELL
WHAT IS A CELL?
The cell is the basic unit of structure
and function in living organisms,
including plants and animals.
TOOL USED TO
The microscope is used to
magnify extremely small objects.
TIMELINE - 1590
Hans and Zacharias Janssen (1590)
Dutch lens grinders
Father and son
Produced first compound microscope
TIMELINE - 1665
Robert Hooke (1665)
Looked at a thin slice of cork through a
compound microscope and observed tiny,
hollow room-like structures.
He called them cells, but he only saw the
outer cell walls because the cork cells
were not alive.
TIMELINE - 1680
Anton van Leeuwenhook (1680)
Dutch amateur scientist
Looked at blood, rain water, and
scrapings from teeth through a
He called the structures he saw
TIMELINE - 1838
Matthias Schleiden (1838)
viewed plant structures under a
microscope and discovered that they
were made of cells.
TIMELINE - 1839
Theodor Schwann (1839)
viewed animal tissue taken from
animal organs under a microscope
and discovered the tissue
was made of cells.
TIMELINE - 1855
Rudoph Virchow (1855)
Stated that living cells come only from
other living cells (This is a part of cell