RIGHT ON 1 2c Vocabulary p.32

All living things are made up of one or more cells. A cell is the smallest unit that can carry on all of the processes of life. Beginning in the 17th century, curious naturalists were able to use microscopes to study objects too small to be seen with the unaided eye. Their studies led them to propose the cellular basis of life. Hooke In 1665, English scientist Robert Hooke studied nature by using an early light microscope, such as the one in Figure 4-1a. A light micro- scope is an instrument that uses optical lenses to magnify objects by bending light rays. Hooke looked at a thin slice of cork from the bark of a cork oak tree. “I could exceedingly plainly perceive it to be all perforated and porous,” Hooke wrote. He described “a great many little boxes” that reminded him of the cubicles or “cells” where monks live. When Hooke focused his microscope on the cells of tree stems, roots, and ferns, he found that each had similar little boxes. The drawings that Hooke made of the cells he saw are shown in Figure 4-1b. The “little boxes” that Hooke observed were the remains of dead plant cells, such as the cork cells shown in Figure 4-1c. SECTION 1 OBJECTIVES ● Name the scientists who first observed living and nonliving cells. ● Summarize the research that led to the development of the cell theory. ● State the three principles of the cell theory. ● Explain why the cell is considered to be the basic unit of life. VOCABULARY cell cell theory Robert Hooke used an early microscope (a) to see cells in thin slices of cork. His drawings of what he saw (b) indicate that he had clearly observed the remains of cork cells (300) (c). FIGURE 4-1 (a) (b) (c) Copyright © by Holt, Rinehart and Winston. All rights reserved. 70 CHAPTER 4 Leeuwenhoek The first person to observe living cells was a Dutch trader named Anton van Leeuwenhoek. Leeuwenhoek made microscopes that were simple and tiny, but he ground lenses so precisely that the magnification was 10 times that of Hooke’s instruments. In 1673, Leeuwenhoek, shown in Figure 4-2a, was able to observe a previ- ously unseen world of microorganisms. He observed cells with green stripes from an alga of the genus Spirogyra, as shown in Figure 4-2b, and bell-shaped cells on stalks of a protist of the genus Vorticella, as shown in Figure 4-2c. Leeuwenhoek called these organisms animalcules. We now call them protists. THE CELL THEORY Although Hooke and Leeuwenhoek were the first to report observ- ing cells, the importance of this observation was not realized until about 150 years later. At this time, biologists began to organize information about cells into a unified understanding. In 1838, the German botanist Matthias Schleiden concluded that all plants were composed of cells. The next year, the German zoologist Theodor Schwann concluded the same thing for animals. And finally, in his study of human diseases, the German physician Rudolf Virchow (1821–1902) noted that all cells come from other cells. These three observations were combined to form a basic theory about the cel- lular nature of life. The cell theory has three essential parts, which are summarized in Table 4-1. Anton van Leeuwenhoek (1632–1723) is shown here with one of his hand-held lenses (a). Leeuwenhoek observed an alga of the genus Spirogyra (b) and a protist of the genus Vorticella (c). FIGURE 4-2 TABLE 4-1 The Cell Theory All living organisms are composed of one or more cells. Cells are the basic units of structure and function in an organism. Cells come only from the reproduction of existing cells. (a) (b) (c) www.scilinks.org Topic: Cell Theory Keyword: HM60241 mb06se_csfs01.qxd 5/18/07 10:54 AM Page 70

Here is a quiz based on the “Reciprocal of a Linear Function” content from your PowerPoint. --- Quiz: Reciprocal of a Linear Function Multiple Choice (5 questions) Select the best answer. 1. What is the vertical asymptote of f(x) = \dfrac{1}{x - 3}? a) x = 0 b) x = 3 c) x = -3 d) y = 0 2. For f(x) = \dfrac{1}{2x + 4}, what is the y-intercept? a) 0 b) \dfrac{1}{2} c) \dfrac{1}{4} d) 2 3. What is the horizontal asymptote of any function of the form f(x) = \dfrac{1}{ax + b} (with a \neq 0)? a) y = 0 b) y = 1 c) x = 0 d) x = -\dfrac{b}{a} 4. The domain of f(x) = \dfrac{1}{5 - x} is a) all real numbers except 5 b) all real numbers except -5 c) all real numbers d) all real numbers except 0 5. As x approaches the vertical asymptote from the right, the values of f(x) a) approach 0 b) approach \pm\infty c) approach 1 d) approach the same value as from the left --- Completion (5 questions) Fill in the blank with the correct word or expression. 1. The vertical asymptote of a reciprocal linear function occurs where the ____________________ is zero. 2. The horizontal asymptote of f(x) = \dfrac{1}{ax + b} is the line y = ________. 3. A function of the form f(x) = \dfrac{1}{ax + b} has ______ x-intercept(s) because the numerator is constant. 4. The end behavior of f(x) = \dfrac{1}{x - 2} as x \to \infty is f(x) \to ________. 5. The y-intercept of f(x) = \dfrac{1}{3x - 6} is ________. --- Answer Key Multiple Choice 1. b) x = 3 2. c) \dfrac{1}{4} (Substitute x = 0: f(0) = \frac{1}{4}) 3. a) y = 0 4. a) all real numbers except 5 5. b) approach \pm\infty Completion 6. denominator 7. 0 8. no / zero 9. 0 (from the positive side) 10. -\dfrac{1}{6} (Substitute x = 0: f(0) = \frac{1}{-6})

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