HistoryHistory

Robert HookeRobert Hooke

In 1633 cut a thin In 1633 cut a thin slice of cork tissue slice of cork tissue and observed it with and observed it with a microscope. These a microscope. These “little boxes” “little boxes” reminded him of the reminded him of the small rooms in which small rooms in which monks lived, so he monks lived, so he called them cellscalled them cells. .

What Hooke had What Hooke had observed were observed were actually actually individual plant individual plant cells.cells.

Anton van LeeuwenhoekAnton van Leeuwenhoek

Was the first Was the first person to observe person to observe living cells in 1674living cells in 1674

Living Cells Living Cells

About 200 years About 200 years passed before passed before scientists began to scientists began to organize the organize the observations of observations of Hooke and van Hooke and van Leeuwenhoek into a Leeuwenhoek into a unified theory.unified theory.

Matthias SchleidenMatthias Schleiden

In 1838 this In 1838 this German botanist German botanist concluded that all concluded that all plants were plants were composed of cellscomposed of cells

Theodor SchwannTheodor Schwann

A year later this A year later this German zoologist German zoologist came to the same came to the same conclusion about conclusion about animals. animals.

Rudolph VirchowRudolph Virchow

In 1855 a German In 1855 a German physician physician determined that determined that cells come only cells come only from other cellsfrom other cells. .

Cell TheoryCell Theory

The observations of there three scientists, The observations of there three scientists, taken together, are known as the Cell Theorytaken together, are known as the Cell Theory

Cell TheoryCell Theory

This theory has three parts:This theory has three parts:

1. All organisms are composed of one or 1. All organisms are composed of one or more cellsmore cells

2. The cell is the basic unit of organization of 2. The cell is the basic unit of organization of organisms.organisms.

3. All cells come from preexisting cells3. All cells come from preexisting cells

Spontaneous GenerationSpontaneous Generation

States that living States that living organisms are organisms are created from non-created from non-living matterliving matter

This theory was This theory was believed back in believed back in Aristotle’s time Aristotle’s time (4(4thth Century BC) Century BC)

Spontaneous Generation Cont. Spontaneous Generation Cont.

It was common “knowledge” that simple It was common “knowledge” that simple organisms like worms, beetles, frogs, and organisms like worms, beetles, frogs, and salamanders could come from dust, mud, etc., salamanders could come from dust, mud, etc., and food left out, quickly “swarmed” with life.and food left out, quickly “swarmed” with life.

Example Example Observation:Observation: Every year in the spring, the Every year in the spring, the

Nile River flooded areas of Egypt along the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of enabled the people to grow that year’s crop of food. However, along with the muddy soil, food. However, along with the muddy soil, large numbers of frogs appeared that weren’t large numbers of frogs appeared that weren’t around in drier times. around in drier times. Conclusion:Conclusion: It was perfectly obvious to people It was perfectly obvious to people

back then that muddy soil gave rise to the frogsback then that muddy soil gave rise to the frogs

Observation:Observation: In many parts of Europe, In many parts of Europe, medieval farmers stored grain in barns with medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice grain, and of course there were lots of mice around. around. Conclusion:Conclusion: It was obvious to them that the mice It was obvious to them that the mice

came from the moldy grain. came from the moldy grain.

If meat was left out If meat was left out usually over time it usually over time it would spoil and maggots would spoil and maggots would begin to grow and would begin to grow and develop. Many people develop. Many people who believed in who believed in spontaneous generation spontaneous generation thought that raw meat thought that raw meat produced maggots.produced maggots.

Therefore, several people Therefore, several people widely held that maggots widely held that maggots arose spontaneously in arose spontaneously in rotting meat rotting meat

They didn’t realize that They didn’t realize that there were flies who laid there were flies who laid eggs which led to eggs which led to maggotsmaggots

After testing this After testing this theory it was theory it was concluded that only concluded that only flies could produce flies could produce other flies!other flies!

Louis PasteurLouis Pasteur

The theory of spontaneous generation The theory of spontaneous generation was finally laid to rest in 1859 by the was finally laid to rest in 1859 by the young French chemist, Louis Pasteur. He young French chemist, Louis Pasteur. He boiled meat broth in a flask, heated the boiled meat broth in a flask, heated the neck of the flask in a flame until it neck of the flask in a flame until it became pliable, and bent it into the shape became pliable, and bent it into the shape of an S. Air could enter the flask, but of an S. Air could enter the flask, but airborne microorganisms could not - they airborne microorganisms could not - they would settle by gravity in the neck. would settle by gravity in the neck.

Louis Pasteur Cont. Louis Pasteur Cont.

As Pasteur had expected, no microorganisms As Pasteur had expected, no microorganisms grew. When Pasteur tilted the flask so that the grew. When Pasteur tilted the flask so that the broth reached the lowest point in the neck, broth reached the lowest point in the neck, where any airborne particles would have where any airborne particles would have settled, the broth rapidly became cloudy with settled, the broth rapidly became cloudy with life. Pasteur had both refuted the theory of life. Pasteur had both refuted the theory of spontaneous generation and convincingly spontaneous generation and convincingly demonstrated that microorganisms are demonstrated that microorganisms are everywhere - even in the air. everywhere - even in the air.

Louis PasteurLouis Pasteur

How was this idea finally disproved?How was this idea finally disproved?