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Chapter 04-1 - Introduction A The use of art to help...

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 Chapter 4 Lecture Outline Introduction The Art of Looking at Cells A. The use of art to help illustrate difficult concepts being discussed has a long tradition in biology. B. Review: All organisms are composed of cells (Module 1.3). C. Cells are at a scale just below what humans can visibly perceive, but with a microscope, we can plainly see that all living things contain cells. D. The focus of this chapter is on the structure and function of the cell and the organelles that are found inside the cell. I. Introduction to the Cell Module 4.1 Microscopes provide windows to the world of the cell. A. Images formed by microscopes represent the object “under” the microscope. A picture of a microscopic image is called a micrograph. B. Magnification: the number of times larger the image appears than the true size of the object. C. Resolution: clarity of the image (resolving power; the ability to distinguish two objects as separate). D. Five types of microscopes that produced the images in the text form images in different ways. Each of these microscopes has advantages relative to the others, and a range of scales at which it functions best. E. Light microscopes (LM) bend the light coming through an object. The bent light rays form larger images in the viewer’s eyes (Figure 4.1A). Well-resolved LM images are limited to 1,000 to 2,000 times larger than life size. The LM is particularly good for looking at living cells and cells and tissues that have been stained (Figure 4.1B). NOTE: Review the units of measure used in science that can be found in the table and in Appendix 1. F. Electron microscopes (EM) use electrons to visualize an object and can magnify images 100 times more than LM. Scanning electron microscopes (SEM) compose images on a TV screen, from electrons that bounce off the surfaces of the object. SEM images are usually about 10,000– 20,000 times larger than life size. The SEM is particularly good for showing organismal and cellular surfaces under high magnification (Figure 4.1C). G. Transmission electron microscopes (TEM) compose images on camera film, from electrons that have traveled through very thin slices of the object and have been bent by magnetic lenses. TEM images are usually about 100,000–200,000 times larger than life size. The TEM is particularly useful for showing the internal structures of cells (Figure 4.1D). H. Modifications to LM have enhanced the imaging process. Two important advancements in LM are the differential interference-contrast and the confocal microscope (Figures 4.1E and F). The former is good for live specimens, while the latter uses fluorescence and lasers to visualize cellular details.
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Module 4.2 Most cells are microscopic. A. Review: the scales of life (compare with Figure 1.1) (Figure 4.2A). B. Bacteria are the smallest cells (approximately 0.2 m m) and are at the lower limits of LM.
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