APPENDIX 1 The Cell Theory The following four points will re-acquaint you with the fundamental principles of the cell theory: 1. The cell is the basic structural unit of living things. This means that every living thing, no matter how large, is composed of cells. 2. The cell is the basic functional unit of living things. This means that the life functions of an organism are carried out at the cellular level. The first two points of the cell theory were well accepted by 1840. The third, which was first stated by 1858, was not fully understood or accepted until 1864. That was when Louis Pasteur demonstrated in a series of experiments that living organisms only arise from living organisms. Since the time of Greek philosopher and scientist Aristotle (384–322 B.C.E.), it had been commonly believed that living things could arise spontaneously from non-living matter. 3. All cells are derived from pre-existing cells. This means that life does not arise spontaneously; it arises from pre-existing cells. 4. In a multicellular organism, the activity of the entire organism depends on the total activity of its independent cells. Background The cell theory developed in a climate of great scientific activity during the 1800s. Improved glass-making technology had made it possible to manufacture reliable compound microscopes on a large scale and at a reasonable price. As a result, hundreds of curious naturalists began peering into the microscopic world. The development of stains for specimens improved the ability of scientists to make observations, and the theories and discoveries made in other scientific disciplines spurred on the quest to learn more about cells. In 1808, John Dalton (1766–1844) published his atomic theory, which described matter as being made up of numerous, tiny units called atoms. This idea suggested a new line of investigation. What if living things were also made of small units? Investigating this question revealed that plants and animals are made of cells and that these cells have many features in common. This is why biologists say that the cell is the unifying structure that links all life — despite the cell’s great diversity of form. 624 MHR • Appendix 1 The first recorded cell observations (shown here) were reported in 1665 by Robert Hooke (1635–1703). To obtain them, Hooke used a double-lens compound light microscope. Its optical design was similar to the optical design of the microscopes in your school laboratory. The dead cork cells that Hooke observed were hollow, and the rectangular shape of their walls reminded him of the small cells (sleeping rooms) in a monastery. Biologists have used the word “cell” ever since. The first observations of a living cell were made sometime before 1674. In that year, Anton von Leeuwenhoek (1632–1723) accurately drew and described such organisms as bacteria for the first time.
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