Cell Theory

Spontaneous generation Spontaneous generation: the theory that living things came forth from nonliving things because the nonliving material contained pneuma, or "vital heat". Aristotle (384 – 322 BC) lay the foundations for this theory in his book, The History of Animals. The creature generated was dependent on the proportions of this pneuma and the five elements he believed comprised all matter.[3] While Aristotle recognized that many living things emerged from putrefying matter, he pointed out that the putrefaction was not the source of life, but the byproduct of the action of the "sweet" element of water.[5] Mice were thought to spontanously generate from rags and wheat Maggots from rotting meat. http://biology.clc.uc.edu/courses/bio114/spontgen.htm a seventeenth century recipe for the spontaneous production of mice required placing sweaty underwear and husks of wheat in an open-mouthed jar, then waiting for about 21 days, during which time it was alleged that the sweat from the underwear would penetrate the husks of wheat, changing them into mice

The Cell Theory In 1595 Zacharias Jansen, of Middleburg Holland, created the first compound (more then one lens) light microscope. The debate over spontaneous generation continued for centuries. In 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, was not convinced, and he 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.

The cell theory continued…. The cell was first discovered by Robert Hooke in 1665. He examined very thin slices of cork and saw a multitude of tiny pores that he remarked looked like the small rooms monks lived in at a monastery. Because of this association, Hooke called them cells. However, Hooke did not know their real structure or function His cell observations gave no indication of the nucleus and other organelles found in most living cells

The cell theory continued…. Antony van Leeuwenhoek – In 1674, he first man to witness a live cell under a microscope. He called the moving organisms “wee beasties”. Note that this is only 9 years after hookes observation

The Original cell theory : In 1838 scientist Matthias Schleiden and Theodor Schwann, struck by the similarities between plant and animal cells, developed the cell theory: The cell is the unit of structure, physiology, and organization in living things The cell retains a dual existence as a distinct entity and a building block in the construction of organisms Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation) In 1838, Theodor Schwann and Matthias Schleiden were enjoying after-dinner coffee and talking about their studies on cells. It has been suggested that when Schwann heard Schleiden describe plant cells with nuclei, he was struck by the similarity of these plant cells to cells he had observed in animal tissues. The two scientists went immediately to Schwann's lab to look at his slides. Schwann published his book on animal and plant cells (Schwann 1839) the next year, a treatise devoid of acknowledgments of anyone else's contribution, including that of Schleiden (1838). He summarized his observations into three conclusions about cells:    1)  The cell is the unit of structure, physiology, and organization in living things.    2)  The cell retains a dual existence as a distinct entity and a building block in the                         construction of organisms.    3)  Cells form by free-cell formation, similar to the formation of crystals (spontaneous generation).

The cell theory continued… In 1862 Loisis Pasteur provided proof that cells arise from other cell thus disproving the theory of spontaneous generation.

Pasteur’s experiment: a) As his control, Pasteur used flasks with straight necks that permitted bacteria to settle into the broth. In these flasks, the broth was soon teaming with bacteria

b) Pasteur's experimental flasks had long S-shaped necks b) Pasteur's experimental flasks had long S-shaped necks. With such necks bacteria could not enter, even though they were exposed to air. Therefore no bacteria grew.   c) When the S-shaped neck was removed bacteria began to grow in the sterile media.

Modern Cell Theory 1. All organisms are composed of one or more cells 2. The cell is the basic unit of structure and organization of organisms 3. All cells come from preexisting cells. #2 although organisms such as humans, dogs and trees can become very large and complex, the cell remains the simplest, most basic component of any organism

light microscopes Pros Cons Enables the user to see living cells in action The user is Able to see colors Cons cannot be used to distinguish objects that are smaller than half the wavelength of light To see tiny particles under a microscope, scientists must bypass light altogether and use a different sort of "illumination," one with a shorter wavelength.

The electron microscope Pros: The wavelength of electrons are extremely short. electron microscopes can make it possible to view objects as small as the diameter of an atom. (a magnification of 1,000,000x) Cons: no living specimen can survive under their high vacuum produced. they cannot show the ever-changing movements that characterize a living cell. Things cannot be seen in color. It takes light waves to see in color. Because no light is used, color cannot be seen.

Antony van Leeuwenhoek Light microscope Electron microscope