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include chemical, electrical, heat, light, kinetic, and potential. The farther away from the nucleus an electron is, the greater the amount of energy required to keep it there.

9. Cells are composed of carbon, hydrogen, oxygen, and nitrogen, with a little phosphorus and potassium, plus small amounts of other elements. A plant may convert the simple molecules or ions it recycles or absorbs from the soil to very large, complex molecules. Organic molecules are usually large polymers that have a "backbone" of carbon atoms.

10. Carbohydrates contain carbon, hydrogen, and oxygen in a ratio of 1C:2H:1O. Carbohydrates occur as mono-saccharides (simple sugars) and disaccharides (two simple sugars joined together). Polysaccharides may consist of many simple sugars condensed together; others are more complex. Simple sugars, when they are attached to one another, each give up a molecule of water, forming starch. Hydrolysis involves restoring a water molecule to each simple sugar when starch is broken down during digestion.

11. Lipids (e.g., fats, oils, and waxes), which are insoluble in water, consist of a unit of glycerol or other alcohol with three fatty acids attached. They contain carbon, hydrogen, and oxygen, with proportionately much less oxygen than is found in carbohydrates. Saturated fats have hydrogen atoms attached to every available attachment point of their carbon atoms; if there are very few places for hydrogen atoms to attach, the fat is said to be polyunsaturated. Phospholipids have a phosphate group replacing one fatty acid.

12. Proteins are usually large molecules composed of subunits called amino acids. Each amino acid has an amino group (-NH2) and a carboxyl group (-COOH); these groups bond amino acids together, forming polypeptide chains; the bonds are called peptide bonds. Enzymes are large protein molecules that function as organic catalysts. Their names end in -ase. Some have important industrial uses.

13. There are two nucleic acids (DNA and RNA) associated primarily with cell nuclei. DNA and RNA molecules consist of chains of nucleotides. Four kinds of nucleotides, each with a unique nitrogenous base, occur in DNA. Helical coils of DNA contain coded information determining the nature and proportions of substances in cells and the ultimate form and structure of the organism. RNA has a different sugar and nucleotide.

Review Questions

1. What distinguishes a living organism from a nonliving object, such as a rock or a tin can?

2. What is meant by the term organic?

3. How are acids, bases, and salts distinguished from one another?

4. Distinguish among carbohydrates, lipids, and proteins.

5. What is energy, and what forms does it take?

6. How are polymers formed?

7. How is a protein molecule different from a nucleic acid molecule?

Discussion Questions

1. Can part of an organism be alive while another part is dead? Explain.

2. What is the difference between inherited form and form resulting from response to the environment?

3. What might happen if all enzymes were to work at half their usual speed?

Learning Onli nne

Visit our web page at http://www.mhhe.com/botany for interesting case studies, practice quizzes, current articles, and animations within the Online Learning Center to help you understand the material in this chapter. You'll also find active links to these topics:

Chemistry of Biology

Inorganic Chemistry

Atoms

Molecules

Bonds

Carbon

Water

Organic Chemistry Lipids

Nucleic Acids Proteins

Additional Reading

Boyer, P. D. 1998. Introductory biochemistry. Belmont, CA: Wadsworth.

Day, W. 1996. Bridge from nowhere, vol. II, The photonic origin of matter. Cambridge, MA: Rhombics.

Lehninger, A. L., D. L. Nelson, and M. M. Cox. 2000. Principles of biochemistry, 3d ed. New York: St. Martin's Press.

Lewis, R. 1994. The beginnings of life. Dubuque, IA: McGraw-Hill.

Margulis, L., et al. (Eds.). 2000. Environmental evolution: Effects of the origin and evolution of life on planet earth, 2d ed. Cambridge, MA. MIT Press.

Raven, P. H., R. F. Evert, and S. E. Eichhorn. 1999. Biology of plants, 6th ed. New York: Worth.

Sackheim, G. 1998. Introduction to chemistry for biology students, 6th ed. Redwood City, CA: Benjamin/Cummings.

Smith, C. A., and E. J. Wood (Eds.). 1991. Biological molecules. New York: Chapman and Hall.

Timberlake, K. C. 1999. An introduction to general organic and biological chemistry, 7th ed. Old Tappan, NJ: Addison Wesley.

Old Light Plants

Phloem of Douglas fir (Pseudotsuga menziesii), X500. (Polarized light photomicrograph by G. S. Ellmore.)

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Low Carb Diets Explained

Low Carb Diets Explained

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