ch03.1 - Cellular Basis of Life

Cells also vary dramatically in the functions or

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Cells also vary dramatically in the functions, or roles, they play in the body. For example, white blood cells wander freely through the body tissues and protect the body by destroying bacteria and other foreign substances. Some cells make hor- mones or chemicals that regulate other body cells. Still others take part in gas exchanges in the lungs or cleanse the blood (kidney tubule cells). Anatomy of a Generalized Cell Although no one cell type is exactly like all others, cells do have the same basic parts, and there are certain functions common to all cells. Here we will talk about the generalized cell, which demon- strates these many typical features. In general, all cells have three main regions or parts a nucleus (nu kle-us), cytoplasm (si to-plazm ), and a plasma membrane (Figure 3.1). The nucleus is usually located near the center of the cell. It is sur- rounded by the semifluid cytoplasm, which in turn is enclosed by the plasma membrane, which forms the outer cell boundary. (Figure 3.4 on p. 67 shows the more detailed structure of the generalized cell as revealed by the electron microscope.) The Nucleus Anything that works, works best when it is con- trolled. For cells, “headquarters,” or the control center, is the gene-containing nucleus ( nucle kernal). The genetic material, or deoxyribonucleic acid (DNA), is much like a blueprint that contains all the instructions needed for building the whole Chapter 3: Cells and Tissues 63 Chromatin Nuclear envelope Nucleus Nucleolus Nuclear pores Rough ER (a) (b) Nucleus Cytoplasm Plasma membrane FIGURE 3.1 Anatomy of the generalized animal cell nucleus. (a) Orientation diagram: The three main regions of the generalized cell. (b) Structure of the nucleus.
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