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Unformatted text preview: 89 Cells: What Are the Building Blocks of Life? Organisms are made up of cells much as societies are made up of individual beings, and for much the same reasons. Isaac Asimov, 1988 Chapter opening photo Root tip cell from an onion. This color-enhanced photograph was taken by using the transmission electron microscope (magnified 800 times). Overview You might imagine that the torch ignited by Mendel would pass quickly, that Mendels contemporaries would see the importance of the factors that controlled heredity and carry the search forward. But it was not until the turn of the centurylong after his deaththat Mendels work was finally appreciated. There were several reasons. The monastery at Brunn was isolated from the mainstream of 19th-century science. Communication 4 90 C HAPTER 4 Cells: What Are the Building Blocks of Life? among scientists in the mid-1800s lacked the lightning speed of today. Those who did read Mendels work may not have understood it. His use of mathematics in analyzing the results of his experiments was novel, maybe even a bit distasteful, to the gentlemen scientists of the day. His contemporaries may have gotten lost in his numbers. Perhaps the most important reason Mendels work was ignored, however, was that his hereditary factors were not things that could be seen or touched. They were abstract. Mendel could describe how the factors were handed down from parents to offspring, but he could point to no physical entity that behaved like the factors during reproduction. Not until the discovery of chromosomes , the tiny rod-shaped structures that carry the hereditary information within cells, would Mendels work find a place in the mainstream of scientific ideas. Chromosomes, however, would not be understood until the nature of the cells that contain them was fully understood. The mid-19th century was a time of upheaval in biology. Not only was Darwins controversial theory being hotly debated, a new idea was rocking the foundations of the field. This new idea is now called cell theory , and it is the topic of this chapter. 4-1 What Is the Cellular Nature of Life? When you look at an organism such as a tree or a human, what you see is a single being. What you cannot see is the vast community of cells that constitute that being. The cell is the fundamental unit of life, the smallest entity capable of exhibiting the characteris-tics of life. Cells acquire and use energy; they acquire and organize materials; they grow; they reproduce. Trees and humans are composed of trillions of cells working together, but this fact is not immediately obvious.To scientists of the 19th century, the discovery of the cellular basis of life was a surprise....
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This note was uploaded on 01/08/2011 for the course CJS 212 taught by Professor Smith during the Summer '10 term at University of Phoenix.
- Summer '10