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topic 1 - Biology 112 Cells and Organisms - 1 Unit 1...

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Biology 112 Cells and Organisms - 1 Unit 1 Structure and Function of Cells Topic 1 – Cells and Organisms 1.1 Cell Theory CELL THEORY, or cell doctrine, states that all organisms are composed of similar units of organization, called cells. The concept was formally articulated in 1839 by Schleiden & Schwann and has remained as the foundation of modern biology. The idea predates other great paradigms of biology including Darwin's theory of evolution (1859), Mendel's laws of inheritance (1865), and the establishment of comparative biochemistry (1940). Ultrastructure research and modern molecular biology have added many tenets to the cell theory, but it remains as the preeminent theory of biology. The Cell Theory is to Biology as Atomic Theory is to Physics. 1.1.1 Formulation of the Cell Theory In 1838, two German scientists, Theodor Schwann and Matthias Schleiden, had been using microscopes to examine cells in sections of different organisms. 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. After Schwann had seen Schleiden’s slides, he published a book on animal and plant cells (Schwann 1839), without even acknowledging Schleiden (!). Schwann summarized his studies in 3 conclusions about cells: 1) The cell is the unit of structure, physiology, and organization in living things. 2) The cell is both a distinct entity and a building block in the construction of organisms. 3) Cells form by a process that is similar to the formation of crystals (spontaneous generation). The first two conclusions are still solid today, but the third is wrong. It took the work of many other scientists, including Louis Pasture, to disprove spontaneous generation. As a result, we now believe that the third conclusion should be: “cells only arise from pre-existing cells". 1.1.2 Current version of Cell Theory Our understanding of cells is still changing today as more and more is discovered (about microbes in particular). But in general we can state Cell Theory as having the following points that are true about all cells that we know about:
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Biology 112 Cells and Organisms - 2 1. All living things are, or are made up of, cells. 2. The cell is the structural & functional unit of all living things. 3. All cells come from pre-existing cells by division. 4. Cells contains hereditary information which is passed from one generation to the next 5. All cells are based on the same chemistry. 6. Cells trap, and use energy to build, the molecules that make them up (metabolism & biochemistry) Since all cells seem to have the same general properties, in this course on cell biology we will mostly use two types of cells (called Bacteria and Archaea) to describe cell biology. The principles that we will discover will be seen again in courses that deal with eukaryotic cells, which make up most of the multi-cellular organisms. If you are interested in the history of cell theory, there is a useful introduction at:
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topic 1 - Biology 112 Cells and Organisms - 1 Unit 1...

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