Worksheet+1

Cell Theory and Discovery of the Microscope

1. Construct a timeline that charts the development of the microscope and the invention of the cell theory. Include the following scientists:

Jean Baptiste van Helmont Rene Dutrochet Francesco Redi Lazzaro Spallanzani Louis Pasteur Hans Jansen Zacharias Jansen Robert Hooke Anton van Leeuwenhoek Matthias Schleiden Theodor Schwann Rudolf Virchow Ernst Ruska

2. What connection can you describe between the invention of the cell theory and the development of the microscope? Do you think that our knowledge of cells would have developed without the microscope?

3. What was the theory of spontaneous generation? Whose idea was it? Why did he believe it? Who disproved this theory? How?

4. Describe and explain the Cell Theory.

5. Choose one of the scientists from the list above and describe their life and work. Include things like where and when they were born and died, some details about their family life and information about their scientific discoveries.

6. Sir Isaac Newton is said to have claimed that he had been so successful because he had been able to stand on the shoulders of giants. By this we think he meant that by using the work of other scientists he was able to make his own discoveries. Do you think that the development of the microscope and the creation of the cell theory support this idea. This is a “fat” question. You will need to work out what Newton meant first before you can decide if this an example to support his thoughts. **//Here are my answers to the questions above//** 1.
 *  1590 - Dutch spectacle-makers Hans Janssen and his son Zacharias Janssen, claimed by later writers (Pierre Borel 1620 - 1671 or 1628 - 1689 and Willem Boreel 1591 - 1668) to have invented a compound microscope.
 *  1648 - Upon his death, Jean Baptiste van Helmonts works were published, containing, amongst other things, the theory of spontaneous generation.
 *  1665 - Robert Hooke publishes //Micrographia//, a collection of biological micrographs. He coins the word //cell// for the structures he discovers in cork bark by modifing a microscope to include two lenses, thus magnifing the specimen by 30x.
 *  1668 - The first serious attack on the idea of spontaneous generation was made in 1668 by Francesco Redi, an Italian physician and poet. At that time, it was widely held that maggots arose spontaneously in rotting meat. Redi believed that maggots developed from eggs laid by flies. To test his hypothesis, he set out meat in a variety of flasks, some open to the air, some sealed completely, and others covered with gauze. As he had expected, maggots appeared only in the open flasks in which the flies could reach the meat and lay their eggs.
 *  1674 - Anton van Leeuwenhoek improves on a simple microscope for viewing biological specimens.
 *  1745 - John Needham, an English clergyman, proposed what he considered the definitive experiment. Everyone knew that boiling killed microorganisms, so he proposed to test whether or not microorganisms appeared spontaneously after boiling. He boiled chicken broth, put it into a flask, sealed it, and waited - sure enough, microorganisms grew. Needham claimed victory for spontaneous generation. An Italian priest, Lazzaro Spallanzani suggested that perhaps the microorganisms had entered the broth from the air after the broth was boiled, but before it was sealed. To test his theory, he modified Needham's experiment - he placed the chicken broth in a flask, sealed the flask, drew off the air to create a partial vacuum, then boiled the broth. No microorganisms grew. Proponents of spontaneous generation argued that Spallanzani had only proven that spontaneous generation could not occur without air.
 * 1832 - Rene Dutrochet showed that gas exchange in plants was via minute openings (stomata) on the surface of leaves and the deep cavities with which they communicate. He further demonstrated that only cells containing chlorophyll can fix carbon and thus transform light energy into chemical energy. Dutrochet studied osmosis and suggested it may be the cause of ascent and descent of in plants.
 *  1838 - Matthias Schleiden stated that all plants are made of cells.
 *  1839 - Matthias Schleiden and Theodor Schwan developed the first two principles of the cell theory... 1. All living things are made of cells. 2. Cells are the basic units of structure and function in living things.
 *  1858 - Rudolf Virchow developed the third principle of the cell theory... 3. All cells arise from pre existing cells.
 *  1859 - Louis Pasteur finally disproved the theory of spontaneous generation.
 *  1863 - Louis Pasteur found that bacteria causes disease.
 * == 1931 - Ernst Ruska starts to build the first electron microscope. It is a Transmission electron microscope (TEM) ==

2. Cell theory developed along with the microscope. Cells are too small to be see in detail by the naked eye so without microscopes our knowledge of cells would have been very limited.
== 3. The theory of spontaneous generation was that life suddenly appeared where seemingly no life previously existed. This was proposed by Jean Baptiste van Helmont who believed this because he observed that life appeared in places where it seemed that life could not have reached other than spontaneously. This theory was disproved by Louis Pasteur who made a broth in which all the ingredients for life was contained, which he put into several beakers. He then sealed each beaker, the first with a straight tube open to the air, the second with a tube containing one bend, the third with two bends and finally, the fourth with no tube. This experiment showed that the first beaker containing the tube with no bend had lots of life in it, the second had some life in it, the third had no life in it due to the opening facing downwards, so the life could not escape into it, and the fourth had no life in it either. According to Jean Baptiste van Helmont, there should have been lots of life in every one of these beakers because there was food contained in them, so life should have spontaneously generated. Pasteurs experiment proved Helmonts theory wrong. == <span style="display: block; font-family: Verdana; font-size: 12pt; font-weight: normal; line-height: 150%;">4. The cell theory is that all living organisms have a simple unit of structure and function, which is the cell. This was an important statement because it suggested that all living things have a common denominator. Almost 200 hundred years of research by many different scientists led to this conclusion. The original discovery of cells was made by Robert Hooke in 1665. He designed one of the first microscopes and used it to look at plant matter. One item he examined was thinly sliced pieces of cork. He looked at the cork through the microscope and saw that it was made up of many small units. He named these units cells and had discovered the basis of all living matter. After Hooke and many others observed samples of plant material, it was discovered that they were also made up of cells. As more material was examined, a pattern was beginning to be recognised. In 1838 a German scientist named Matthias Schleiden declared that all plant material was made up of cells. The year after, Theodor Schwann gave the same conclusion about animals. Their findings are what have become known as the cell theory. With the development of the electron microscope, this theory has continued to improve. More living material has been observed at higher magnifications; so much more has been learned about cells and the cell theory. The modern cell theory includes the two basic components of the classic cell theory and then adds the following: <span style="display: block; font-family: Verdana; font-size: 12pt; font-weight: normal; line-height: 150%;">5. __//**Ernst Ruska**//__ <span style="display: block; font-family: Verdana; font-size: 12pt; font-weight: normal; line-height: 150%;"> <span style="display: block; font-family: Verdana; font-size: 12pt; font-weight: normal; line-height: 150%;">  Ernst Ruska (1906 – 1988) was a German physicist from Heidelberg. He was the fifth child of Julius Ferdinand Ruska, an Asian studies professor, and Elisabeth (Merx) Ruska. After earning his undergraduate education in the physical sciences from the Technical University of Munich and the Technical University of Berlin, he was certified as an electrical engineer in 1931. He then went on to study under Max Knoll at Berlin, and received his doctorate in electrical engineering in 1933. During this period he and Knoll created an early version of the electron microscope. Prior to Ruska's invention of the electron microscope in 1931, the field of microscopy was limited by the inability of existing microscopes to see features smaller than the wavelength of visible light. A prototype of the electron microscope was then developed in 1931 by Ruska and Max Knoll at the Technical University in Berlin. This prototype laid the groundwork for a more powerful version, which Ruska developed in1933. That version was ten times stronger than existing light microscopes. Ruska's microscope--called a transmission microscope--captures on a fluorescent screen an image made by a focused beam of electrons passing through a thin slice of metalized material. transmission microscope, and its inventors shared the 1986Nobel Prize in physics with Ruska. Ruska's work was honored with the Nobel Prize and the Senckenberg Prize of the University of Frankfurt am Main in 1939, the Lasker Award in 1960, and the Duddell Medal and Prize of the Institute of Physics in London in 1975, among other awards. He also held honorary doctorates from the University of Kiev, the University of Modena, the Free University of Berlin, and the University of Toronto. Ruska died in West Berlin on May 30, 1988. <span style="display: block; font-family: Verdana; font-size: 12pt; font-weight: normal; line-height: 150%;">6. I believe that when Isaac Newton said that he stood on the shoulders of giants he meant that the scientists before him had helped him to get where he was. They helped him make his theories and make discoveries that he would not have come by without their help.
 * Organisms can be unicellular or multi-cellular
 * When cells divide, the hereditary information they contain, is passed from cell to cell.
 * Energy flow occurs within cells.
 * All cells have basically the same composition.
 * The activity of the organism is determined by the activity of the independent cells.