The Discovery of Cells How some very smart scientists invented microscopes, which led to the discovery of cells and the development of the Cell Theory and the Germ Theory

All Living Things: Are made up of cells Cell: the basic unit of living things that can perform all the processes associated with life Sense and Respond to Change in their Environment Reproduce Have DNA Obtain and Use Energy Energy: ability to make things move or change Grow and Develop

The Invention of Microscopes During the 1st century AD (year 100), glass was invented and the Romans were looking through the glass and testing it.  They experimented with different shapes of clear glass and one of their samples was thick in the middle and thin on the edges.  They discovered that if you held one of these lenses over an object, the object would look larger.  These lenses were not used much until the end of the 13th century when spectacle makers were producing lenses to be worn as eyeglasses.

Zaccharias and Hans Janssen Sometime around the year 1590, two Dutch spectacle makers, Zaccharias Janssen and his father Hans started experimenting with lenses.  They put several lenses in a tube and made a very important discovery.  The object near the end of the tube appeared to be greatly enlarged, much larger than any simple magnifying glass could achieve by itself!  They had just invented the compound microscope (a microscope that uses two or more lenses). 

Anthony van Leeuwenhoek Anthony van Leeuwenhoek of Holland became very interested in lenses while working with magnifying glasses in a store.  He used the magnifying glass to count threads in woven cloth.  He became so interested that he learned how to make lenses. He made small lenses with great curvatures. 

Leeuwenhoek’s rounder lenses produced greater magnification, and he created microscopes that were able to magnify up to 270 times! These more powerful microscopes led to the discovery that there were many very small organisms that did not belong in the Animal or Plant Kingdoms. Before this time, people did not know that there were organisms smaller than plants or animals!

Anthony van Leeuwenhoek Leeuwenhoek used his microscope to look at scrapings from his own teeth as well as from teeth of 2 old men who had NEVER BRUSHED THEIR TEETH! The term “bacteria” didn’t exist yet, and so he called the organisms he saw “animalcules” In his own words…

"I then most always saw, with great wonder, that in the said matter there were many very little living animalcules, very prettily a-moving. The biggest sort. . . had a very strong and swift motion, and shot through the water (or spittle) like a pike does through the water. The second sort. . . oft-times spun round like a top. . . and these were far more in number." In the mouth of one of the old men, Leeuwenhoek found "an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time. The biggest sort. . . bent their body into curves in going forwards. . . Moreover, the other animalcules were in such enormous numbers, that all the water. . . seemed to be alive." Anthony van Leeuwenhoek September 17, 1683

Leeuwenhoek’s observations What Anthony van Leeuwenhoek observed included bacteria, yeast, blood cells and many tiny animals (protozoans) swimming about in a drop of water.  From his great contributions, many discoveries and research papers, Anthony Leeuwenhoek has since been called the "Father of Microscopy".

Robert Hooke Robert Hooke, an Englishman who is sometimes called the “English Father of Microscopy”, also spent much of his life working with microscopes and improved their design and capabilities. He used a microscope that magnified 30 times (30X) to look at the bark of a cork tree.

Hooke’s Sketch In the thin slice of cork, Hooke saw small areas that looked like small empty rooms, or cells. What he actually saw was the remaining dead walls of plant cells, not living cells.

Cork Tree Bark Cork Tree

Other Key Contributors In 1838, German botanist Matthias Schleiden used the microscope to study parts of plants He concluded that plants were made of cells. One year later, scientist Theodor Schwann, concluded that all animals are made of cells. Together, Schleiden and Schwann concluded that all living things are made of cells.

Key contributors, continued In the mid-1850’s, doctor Rudolph Virchow stated that new cells do not form on their own. All cells come from other living cells. Virchow’s discovery, combined with Schleiden and Schwann’s findings, led to what we know today as… The Cell Theory

The Cell Theory All living organisms are made of one or more cells. All cells are the basic units of structure and function in all organisms. Structure: how something is built—its form Function: what something does—its job All cells come from previously existing cells.

All living organisms are made of one or more cells Living organisms can be single-celled, like these bacteria Or multi-cellular, like the tapir, swordfish, and tree.

2. Cells are the basic units of structure and function in all organisms Examples: Bone cells, nerve cells (neurons), blood cells, skin cells, muscle cells, etc. Leaf cells, root cells, flower cells, cells that make up a plant’s transport tissues (xylem and phloem)

Blood Cells Skin Cells Rod & Cone Eye Cells Neuron Bone Cells

3. All cells come from previously existing cells Cells come from other cells when they divide through a process called Mitosis. 2 Identical Daughter Cells

Knowing about cells is useful! Back in the 1800’s, there were no refrigerators like we have today. Food often spoiled and milk went sour. A French scientist, Louis Pasteur, proved that microscopic organisms led to food spoilage and disease.

Pasteurization Pasteur noticed that spoiled beverages contained large amounts of bacteria. He created a process in which heat was used to kill the bacteria, thereby keeping beverages fresh longer. This process, called pasteurization, is still used today. Check your milk cartons at lunch and at home for the word “pasteurized”

Germ Theory Pasteur is the most famous of the many scientists who developed the Germ Theory The Germ Theory, in simplest terms, states that many diseases are caused by microorganisms. Over time, acceptance of this theory led to doctors washing their hands before surgery development of medicines like antibiotics

Main Idea The following sentences are all facts from today’s lesson. Only one sentence below represents the main idea of today’s power point. Circle the main idea sentence. Our bodies are made of cells Scientific knowledge develops over time, often with contributions from more than one scientist. Pasteurization is important for keeping our food safe.

Isaac Newton (in a letter to Robert Hooke dated February 5, 1676) When scientists announce their discoveries they refer to the following quote: “If I have seen a little further it is by standing on the shoulders of Giants” Isaac Newton (in a letter to Robert Hooke dated February 5, 1676) How does this quote apply to Louis Pasteur and his discovery?