1. All Living Things Are Composed Or Made of Cells

Cell Theory In 1595, a Dutch spectacle maker Zacharias Janssen produced the first compound microscope. A compound microscope uses two convex or curved lenses housed within a tube. With the help of light the two lens can enlarge the image of an object. Fifty years later in the mid-1600s an English scientist named Robert Hooke became the first to use a microscope to observe the cellular structure of plants. While observing a piece of cork under a microscope, he noticed a number of tiny, empty compartments that reminded him of the cells or rooms monks used in a monastery. He called these tiny compartments in the cork a cell. Since Hooke was looking at cork which is the bark from an oak tree, he did not view living cells but the remnants of the plant cell. We know today that he was seeing only the cell wall of the plant cell. A few years later a tradesman from Holland named Anton van Leeuwenhoek became the first person to use a microscope to observe living cells such as bacteria, one celled organisms called protists, and blood cells. Besdies viewing hundreds of living cells Leeuwenhoek is remembered for constructing and modifying hundreds of microscopes in his lifetime.

In the 1800s, discoveries made by three German scientists would lead to the development of the cell theory. In 1838, while observing plant tissue with the aid of a microscope, Matthias Schleiden discovered that all plant parts were made up of cells. He went on to state that all plants were composed of cells. Then in 1839, Theodor Schwann used a microscope to view various animal tissues and stated that all animals were made up of cells. Approximately 20 years later, from his research Rudolph Virchow concluded that living cells come from other living cells. Virchow combined the work of Schleiden and Schwann with his research and developed the first cell theory. The cell theory includes 3 components: 1. All living things are composed or made of cells. 2. Cells are the smallest unit or structure that can carry out the processes or functions necessary for life. 3. Cells can only come from other living cells.

Microscopes Microscopes-An instrument that produces an enlarged image of an object Magnification- causes an increase in an object’s apparent size. Resolution-the power of a microscope to clearly show detail Types of microscopes 1. Compound Light Microscopes a. With this type of microscope the specimen is mounted on a glass slide. b. Light passes through the specimen and through the objective lens. c. A set of objective lenses is located on the rotating nosepiece and they enlarge the image of the specimen with different powers of magnification. d. To compute the total magnification of a microscope, multiply the power of magnification, (40X or 100X); of the lens being used by the power of the magnification of the eyepiece lens (10X). Ex. 40 X 10 = 400X total power of magnification 2. Electron Microscopes a. Used to a view extremely small objects b. Use Beam of Electrons instead of light c. More powerful than compound light microscopes 3. Types of Electron Microscopes A. Transmission Electron Microscope b. Can magnify objects up to 200,000 times c. Projects image onto a screen or photographic plate d. View internal details of specimen e. Cannot be used on live specimens B. Scanning Electron Microscopes a. Produces 3-D image enlarge at least 100,000 times actual size b. Specimens sprayed with fine metal coating c. Beam of electrons pass over the surface of metal coating to emit shower of electrons which are projected onto a screen d. Cannot be used on live specimens