Download The Cell Theory

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The Cell Theory
Since cells cannot be seen with the naked eye, scientists did not know that
cells existed until after the development of the microscope. Anton Van
Leeuwenhoek (1632-1723) was a Dutch scientist and the first person to record
seeing living organisms, which were too small to be seen by the naked eye.
About the same time, in 1665, an Englishman named Robert Hooke,
examined a plant tissue called cork with a crude microscope. He reported that this
tissue all seemed to be made up of boxes. He called these boxes “cella,” the Latin
word for small room, and this translates into English as “cell.” So Robert Hooke
was the first person to use the word “cell” in describing the structure of living
organisms.
However, observers soon realized that sometimes there was a light gray sap
in those boxes. Sometimes they noticed a darker, denser ball floating about in the
sap. This ball caught the attention of Robert Brown. He announced his view in
1831, using the word “nucleus” to describe the structure. (“The word “nucleus” is
Latin for “little nut.”)
In 1839 the cell theory, as it came to be called, was first announced to the
world by two scientists. Matthias Schleiden and Theodor Schwann concluded that
all living things were composed of cells. This was the first statement of the cell
theory.
Twenty years later, Max Schultze pointed out that the cell was the physical
basis of life. Now the cell theory was expanded to include another idea. Not only
was the cell the unit of structure of a living thing, but it was the unit of function as
well. In other words, living things functioned the way they did because their cells
contained a living substance having the properties of life.
In 1855 Rudolf Virchow added the third important part of the cell theory. He
stated that all cells could only come from other cells. At this point then, the cell
theory can be summarized in three parts:
1. All living things are made up of cells.
2. Cells are the basic units of structure and function in living things.
3. All cells can only come from pre-existing cells.
Name:_________________________
Date:________________Hour:_____
Reading Response Questions
1. Who was the first scientist to record seeing living organisms with a microscope?
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2. Who was the first person to use the word “cell”? What was he looking at?
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3. Who is responsible for the word “nucleus”?
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4. What are the three parts of the cell theory?
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