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Exercise 1. the Discovery of Cells

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Exercise 1. the Discovery of Cells Reprinted from Gallik S., Cell Biology OLM Page | 1 Exercise 1. The Discovery of Cells A. Introduction Ancient Greek philosophers famously espoused the idea that life generated spontaneously. Aristotle recognized that some animals come from parent animals of the same kind, but thought that others appear spontaneously from a nonliving substance he called pneuma and from four terrestrial elements, earth, air, fire and water. Aristotle condensed these ideas into a theory that we now call the Theory of Spontaneous Generation. The theory basically states that living organisms form spontaneously, from nonliving matter. Cork (Microscopic magnification 400X) It wasn't until the 1800s that scientists made the important discoveries that unequivovally dispelled the theory of spontaneous generation. One of these developments was the formulation of the Cell Theory. The Cell Theory, one of the fundamental unifying principles of biology, establishes the cell as the basic unit of life. As is summerized in the timeline below, the theory grew out of hundreds of years of scientific research and technical developments, beginning with the development of glass lenses and the microscope and continuing with the discovery of the cell. In this exercise, we trace some of the major events in the history of the development of the microscope, discovery of the cell and the formulation of the cell theory. In lab, we microscopically examine some of the same specimen early biologists examined when they first observed cells and finally came to the conclusion that all living things are made of cells. B. Invention of the Microscope The invention of the glass lens set the stage for the development of the microscope. The earliest glass lenses date back to approximately 700 BC, but it is widely reported that the glass magnifying lens was invented by Roger Bacon in the mid 13th Century. Bacon, an English Franciscan monk, working from the studies of early Arab scientists (circa 1000), investigated the optical properties of glass magnifying Copyright © 2011, 2012, 2013 by Stephen Gallik, Ph. D. Licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. All text falls under this copyright and license. The only figures that fall under this copyright and license are those sourced to Stephen Gallik, Ph. D. Other figures may be copyrighted by others. Go to the on-line lab manual for image attribution & copyright information. Contact author at [email protected] . Reprinted from Gallik S., Cell Biology OLM Page | 2 lenses, which was reported in his major treatis, Opus Majus, written at the request of Pope Clement IV and presented to the Pope in 1267. Glass lenses were first used to correct human eyesight. There is a debate among historians as to when eyeglasses were invented and by whom. Some claim they were invented in Italy about 1286. However others claim they were invented earlier, in India. The first microscopes were developed about 300 years later, the same time the first telescopes were developed, between 1590 and 1610. The first working telescopes were built by Dutch lensmakers at the beginning of the 17th century (1608). Credit for the invention of the telescope is given to three individuals: Hans Lippershey, Zacharias Janssen and Jacob Metius. Zaccharias Janssen is also associated with the invention of the simple and compound light microscopes. Confusion surrounds the role of Zaccharias in the microscope's invention. It is generally reported, and seems highly likely, that Hans Janssen, Zaccharias' father, either helped his son build the first microscope or built the first microscope himself in 1595. Janssen's microscope was a hand-held microscope, The Janssen Microscope consisting of two sliding tubes, each inserted into the end Image Source: Molecular Expressions of a middle stationary tube. The eyepiece lens, which was inserted at one end of one of the sliding tubes, was a bi- convex lens. The objective lens, inserted at the far end of the other sliding tube, was a plano-convex lens. One could focus on the specimen by simply sliding either of the sliding tubes in and out. The micrsocope was capable of magnifications ranging from 3X to 10X. Galileo improved upon the designs of early telescopes and microscopes. He built his first telescope in 1609, a year after the Dutch, and later built improved models. The Galilean telescope characteristically had one concave and one convex lens mounted in a rigid tube. They were the first telescopes to achieve magnifications beyond 10X, with some achieving magnifications of nearly 30X. Using these telescopes, Galileo discovered the moons of Jupiter and many other significant astronomical phenomena. Soon after his work on the telescope, Galileo used the instrument at close range to magnify small objects, and by 1624 he was routinely using his compound microscope. Like Galileo's Microscope the Galilean telescope, the Galilean compound microscope had Image Source: History of the one concave and one convex lens. Galileo's illustrations of Microscope.org Copyright © 2011, 2012, 2013 by Stephen Gallik, Ph. D. Licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. All text falls under this copyright and license. The only figures that fall under this copyright and license are those sourced to Stephen Gallik, Ph. D. Other figures may be copyrighted by others. Go to the on-line lab manual for image attribution & copyright information. Contact author at [email protected] . Reprinted from Gallik S., Cell Biology OLM Page | 3 microscopic views of insects made using one of his microscopes were published in 1625 and appear to be the first clear documentation of the use of a compound microscope. But it wasn't for another 40 years that the first cells were observed, by Robert Hooke and Antoni van Leeuwenhoek. C. Robert Hooke and Antoni van Leeuwenhoek Robert Hooke (1635-1703) was an English chemist, physicist, architect, and surveyor. He designed microscopes, he didn't build them. His designs improved upon microscope mechanics and illumination, which improved resolution and increased the magnification to approximately 50X. These improvements enabled Hooke to microscopically view greater detail of objects smaller than those reported by Galileo. The Hooke microscope consisted of three glass lenses, an eyepiece lens, a bi-convex objective lens and an intermediately-placed tube lens, inserted at various places Robert Hooke's Microscope. along a rigid tube assembly. The tube assembly was Image Source: Molecular Expressions mounted to a base through a moveable joint that permitted adjustment of the incline of the microscope tube. The microscope also used a special illumination system that concentrated light on the specimen, making the final image brighter. Copyright © 2011, 2012, 2013 by Stephen Gallik, Ph. D. Licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. All text falls under this copyright and license. The only figures that fall under this copyright and license are those sourced to Stephen Gallik, Ph. D. Other figures may be copyrighted by others. Go to the on-line lab manual for image attribution & copyright information. Contact author at [email protected] . Reprinted from Gallik S., Cell Biology OLM Page | 4 Hooke used his compound microscope to microscopically study a variety of organisms and biological structures, including thin slices of cork, the outer-most layer of the bark of trees. In 1665, he reported some of his observations in his famous treatise entitled Micrographia, which included his now-famous drawing of his microscopic view of cork. In describing what he observed, Hooke coined the term "cell", in reference to the microscopic compartmental structure he observed. Today, Robert Hooke is credited with the first microscopic view of the cell and is, along with Antoni van Leeuwenhoek, credited with the discovery of the cell. Antoni van Leeuwenhoek (1632-1723), a contemporary of Robert Hooke, was a Dutch draper, tradesman, and amateur scientist. He was also a masterful lensmaker. He taught himself how to grind and polish glass lenses, and he developed a level of lensmaking skill unmatched in his Robert Hooke's drawing of the day. He produced lenses with a magnification greater microscopic image of cork. than 250X, a power that far exceeded the lenses used by Micrographia, 1665. Galileo and Hooke. Image Source: Wikipedia Leeuwenhoek used his lenses to make relatively high quality simple microscopes. His hand-held microscopes were approximately two inches long and contained one of his small, high-quality bi-convex lenses sandwiched between two brass plates. With the specimen mounted on a pin and the entire instrument held up to the light and close to the eye, Leeuwenhoek microscopically viewed biological specimen at a resolution and magnification not attained by any other scientist of his day. He observed and, in 1674, gave the first relatively detailed description of red blood cells, was the first to describe colonial alga Spirogyra and was the first to describe the small unicellular organisms found in pond water, "animalcules" as he called them. In addition, he was the first to observe and describe bacteria and is considered by many to be the "Father of Microbiology". Leeuwenhoek reported his observations to the Royal Society. In 1678 the Royal Society asked Leeuwenhoek's Microscope. Robert Hooke to confirm Leeuwenhoek's findings. Image Source: Molecular Expressions Hooke not only confirmed Leeuwenhoek's findings, but noted that Leeuwenhoek's simple microscope gave clearer images than Hooke's compound microscope. Today, Leeuwenhoek is credited with the first microscopic view of living cells and is, along with Robert Hooke, credited with the discovery of the cell. Copyright © 2011, 2012, 2013 by Stephen Gallik, Ph. D. Licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License. All text falls under this copyright and license. The only figures that fall under this copyright and license are those sourced to Stephen Gallik, Ph.
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