A History of Cells
The Scientists behind Cell Theory
The study of cells started about 330 years ago. Before the invention of the
microscope, we did not know anything about cells. That is because cells are too
small to be seen with just our eyes alone. In 1590, two scientists from the
Netherlands (Hans Lippershey and Zacharias Janssen), invented the first
microscope. This was the very first time that we could see tiny objects. A
whole new world had been discovered!
First Microscope
In 1665, English scientist Robert Hooke looked at small pieces of cork
(from the bark of a cork oak tree) through a microscope. He noticed that
all of the cork pieces had tiny, boxlike structures inside them. Hooke
called them “cells” because they looked like the tiny rooms, called cells,
that monks lived in. Hooke did not know exactly what they were, but he
was the first to identify and name cells. The cork cells were no longer
alive, so all Hooke was able to see were the outer walls of the cells. He
did not see any of the inside parts of the cells…they had already died.
Robert Hooke’s drawing of cork cells
In 1674, a Dutch scientist named Anton van Leeuwenhoek was the first
person to see cells in a living organism. He looked at many different
organisms under a microscope, and saw living cells in all of them. He was
also the first person to see single-celled organisms, which scientists had
never known existed. Leeuwenhoek was the first one to propose the idea
that all living things are made of cells.
Leeuwenhoek’s drawing of
single celled organisms.
Many more years passed while scientists studied cells and tried to figure out
what they were, and what they meant for living things. In 1839, the German
scientists Matthias Schleiden (who studied plants) and Theodor Schwann
(who studied animals), worked together to form the theories about cells that
we use today. They concluded that cells are the “building blocks” of living
things. In other words, cells are the smallest unit of life, and cells join
together to form larger organisms. We now know that their ideas about cells
in plants and animals actually include all types of living things on Earth.
One cell divides in
half to form two cells.
By now, most scientists understood and accepted the idea that living things
were made of cells. But an important question remained – where did cells
come from? How were they created? About 20 years after the work of
Schleiden and Schwann, a scientist named Rudolf Virchow discovered the
answer. In 1959, Virchow (who was the first scientist to study leukemia – or
cancer – cells), proposed that cells came from other cells. In other words,
cells reproduce to form new cells by dividing in two. Once Virchow’s theory
was accepted by scientists, the work of Leeuwenhoek, Schleiden &
Schwann, and Virchow was combined to form the ideas behind cell theory.
Cell theory has 3 parts:
1. All living things are made of cells.
 This includes unicellular organisms, made of only one cell, like a bacteria. It also
includes multicellular organisms, which can be made of trillions of cells, like a human.
2. Cells are the basic building blocks of life.
 For example, every part of your body is built out of cells. This means that cells
themselves are alive. A single cell is the smallest thing that can still be called “alive”.
3. Cells come from other cells.
 Cells reproduce by splitting in half to create new cells.
Examples of Cells
Types of
cells found in
many living
things –
including
humans!
Here are some
single-celled
organisms…
made of only
one cell!