{"id":183,"date":"2019-06-24T12:37:39","date_gmt":"2019-06-24T16:37:39","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/4-2-discovery-of-cells-and-cell-theory\/"},"modified":"2022-01-19T15:39:44","modified_gmt":"2022-01-19T20:39:44","slug":"4-2-discovery-of-cells-and-cell-theory","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/053humanbiology\/chapter\/4-2-discovery-of-cells-and-cell-theory\/","title":{"raw":"4.2\u00a0Discovery of Cells and Cell Theory","rendered":"4.2\u00a0Discovery of Cells and Cell Theory"},"content":{"raw":"Created by:\u00a0CK-12\/Adapted by Christine Miller\n\n[h5p id=\"27\"]\n\nFigure 4.2.1 Human cells viewed with a very powerful tool called a scanning electron microscope.<\/em>\n
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Amazing Cells<\/h1>\n<\/div>\nWhat are these incredible objects? Would it surprise you to learn that they are all human [pb_glossary id=\"1298\"]cells[\/pb_glossary]? Cells are actually too small to see with the unaided eye. It is visible here in such detail because it is being viewed with a very powerful\u00a0tool called a scanning electron microscope.\u00a0Cells may be small in size, but they are\u00a0extremely<\/em>\u00a0important to life. Like all other living things, you are made of cells. Cells are the basis of life, and without cells, life as we know it would not exist. You will learn more about these amazing building blocks of life in this section.\n
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What Are Cells?<\/h1>\n<\/div>\nIf you look at living matter with a\u00a0microscope\u00a0\u2014 even a simple light microscope \u2014 you will see that it consists of [pb_glossary id=\"1298\"]cells[\/pb_glossary]. Cells are the basic units of the structure and function of living things. They are the smallest units that can carry out the processes of life. All organisms are made up of one or more cells, and all cells have many of the same structures and carry out the same basic life processes. Knowing the structure of cells and the processes they carry out is necessary to an understanding of life itself.\n
\n\n[caption id=\"attachment_180\" align=\"alignright\" width=\"421\"]\"Diagram Figure 4.2.2 Robert Hooke sketched the cork cells as they appeared under a simple light microscope.<\/em>[\/caption]\n

Discovery of Cells<\/h2>\n<\/div>\nThe first time the word\u00a0cell<\/em>\u00a0was used to refer to these tiny units of life was in 1665 by a British scientist named Robert Hooke<\/a>.\u00a0Hooke was one of the earliest scientists to study living things under a\u00a0microscope. The microscopes of his day were not very strong, but Hooke was still able to make an important discovery. When he looked at a thin slice of cork under his microscope, he was surprised to see what looked like a honeycomb. Hooke made the drawing in the figure\u00a0to the right\u00a0to show what he saw. As you can see, the cork was made up of many tiny units. Hooke called these units\u00a0cells<\/em>\u00a0because they resembled cells in a monastery.\n
\n\nSoon after Robert Hooke discovered cells in cork, Anton van Leeuwenhoek<\/a> in Holland made other important discoveries using a microscope. Leeuwenhoek made his own microscope\u00a0<\/span>lenses, and he was so good at it that his microscope was more powerful than other microscopes of his day. In fact, Leeuwenhoek\u2019s microscope was almost as strong as\u00a0<\/span>modern\u00a0<\/em>light microscopes.\u00a0Using his microscope, Leeuwenhoek was the first person to observe human cells and\u00a0<\/span>bacteria.<\/span>\n\n<\/div>\n
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Cell Theory<\/h2>\n<\/div>\nBy the early 1800s, scientists had observed cells of many different organisms. These observations led two German scientists named Theodor Schwann<\/a> and Matthias Jakob Schleiden<\/a> to propose\u00a0cells as\u00a0the basic building blocks of all living things. Around 1850, a German doctor named Rudolf Virchow<\/a> was studying cells under a microscope, when he happened to see them dividing and forming new cells. He realized that living cells produce new cells through division. Based on this realization, Virchow proposed that living cells arise only from other living cells.\n\nThe ideas of all three scientists \u2014 Schwann, Schleiden, and Virchow \u2014 led to [pb_glossary id=\"1327\"]cell theory[\/pb_glossary], which is one of the fundamental\u00a0theories\u00a0unifying all of biology.\n\nCell theory states that:\n