Name: ____________________________________________ Date: ________________________________
Cell Theory
There are FOUR main ideas outlined in the cell theory:
1. All living things are MADE of one or more CELLS.
2. Cells are the basic units (the building blocks) of LIFE and EXIST in all
organisms.
3. All CELLS come from previously existing CELLS (they do not just
spontaneously generate i.e. come out of nowhere).
4. The proper functioning of an ORGANISM (living thing) depends on the
combined activity of ALL of its individual CELLS.
History
We only began to learn about cells with the invention of the
microscope in the late 1600’s. It was English scientist, Robert HOOKE
(1635–1703), who first recorded his DISCOVERY of CELLS. In 1663, he
took a thin slice of CORK and placed it under a microscope that he
built himself. Hooke called the box-like structures “CELLULAE” (which
meant “little rooms” in Latin) because that’s exactly what they
reminded him of.
Around the same time, Anton van LEEUWENHOEK (1632–1723), a
Dutch craftsman who made lenses, used them to build a simple
microscope. With his microscope, he looked at pond water, BLOOD,
and scrapings from his teeth. He was the first to observe organisms
made of one cell. He called these single-celled organisms
“ANIMALCULES”.
As microscopes improved, scientists made more discoveries. In 1839,
German botanist Matthias SCHLEIDEN and zoologist Theodore
SCHWANN, viewed PLANT and animal tissues under a microscope.
They concluded that all ANIMALS and PLANTS were made up of
CELLS.
Scientists knew that cells existed, but what they didn’t know was
where they came from. In the 1800’s it was BELIEVED that living things
came from NON-LIVING matter (ex. air and water). Did cells come
from nonliving objects? In 1858, a German physician named Rudolf
Virchow (1821–1902) proposed that cells can ONLY come from
ALREADY EXISTING CELLS.