CA 2

Reviewing Content

1.c

2.d

3.b

4. b

5.b

6.d

7.c

8.c

9. a

10. d

Understanding Concepts

11. Elements are composed of atoms. Compounds are composed of atoms of two or more elements combined in definite proportions.

12. Radioactive isotopes are isotopes whose nuclei are unstable and break down at a constant rate over time. Radioactive isotopes are used in determining the ages of rocks, treating cancer, killing bacteria in food, and following the movements of substances within organisms.

13. Atoms in a compound are held together by a chemical bond.

14. Two electrons are shared in a single covalent bond, four in a double bond, and six in a triple bond.

15. Cohesion is an attraction between molecules of the same substance. An example is drops of water forming beads on a smooth surface. Adhesion is an attraction between molecules of different substances. An example is capillary action.

16. A solution is a mixture in which one substance is dissolved in another. The solute is the substance that is dissolved. The solvent is the substance in which the solute is dissolved.

17. An acid is any compound that produces H ions in solution; acidic solutions have pH values below 7. A base is a compound that produces hydroxide ions (OH-) in solution; basic solutions have pH values above 7.

18. Polymers are large macromolecules made up of smaller molecules called monomers. For example, monomers called monosaccharides are joined together to form polymers called polysaccharides.

19. Proteins control the rate of chemical reactions, regulate cell processes, form tissues, transport substances, and help fight disease.

20. Nucleotides consist of a 5-carbon sugar, a phosphate group, and a nitrogenous base.

21. The two basic kinds are ribonucleic acid (RNA), which contains the sugar ribose, and deoxyribonucleic acid (DNA), which contains the sugar deoxyribose.

22. A chemical reaction is a process that changes one set of chemicals into another set of chemicals.

23. Some chemical reactions release energy, and others absorb energy.

24. An enzyme is a biological catalyst.

25. Factors that can influence enzyme activity include pH, temperature, and proteins in cells that help turn key enzymes “on” and “off” at critical stages.

Critical Thinking

26. Adding a base to the solution would increase its pH, because a base produces hydroxide ions in solution and basic solutions have pH values above 7.

27. To carry out all life processes, living things need the energy released in the chemical reactions involved in digesting food.

28. The total product was doubled when the temperature of the reaction increased from 25°C to 35°C, and it decreased to almost zero when the temperature was increased to 45°C. Enzymes work best at certain temperatures. Students should hypothesize that the enzyme involved in this reaction works best at about 35°C, and a much higher temperature inhibits the enzyme’s function.

29. Students might suggest trying to dissolve the solid in water. Lipids are generally not water soluble. They also might suggest warming the solid to see if it would soften, which solid lipids tend to do when heated.

30. The mixture could be separated by adding water. The sodium chloride would dissolve in the water, whereas the silica would not. The salt could be retrieved by filtering the mixture and evaporating the filtrate.

31. The name indicates that carbohydrates contain carbon and the elements in water, oxygen and hydrogen.

32. The diagram should show that hydrogen and chlorine form a covalent bond. Students can use the chlorine atom in Figure 2—3 as a starting point and pair up one of the seven electrons in its outer level with hydrogen’s single electron.

33. If the temperature or pH were changed, the shape of the enzyme hexokinase could change. It might lose its ability to bind with the substrates, glucose and ATP, and an enzyme-substrate complex would not form. As a result, the enzyme would not speed up the reaction.

34. Students should infer that magnesium hydroxide is a base. The base reacts with the acid in the stomach, and forms a product that is not acidic.

35. The fit of an enzyme and a substrate at the enzyme’s active site is so precise that the substrate is like a key and the enzyme is like a lock. Like a key in a lock, only a substrate of a certain shape can fit into the active site of the enzyme. What occurs when a key is inserted into a lock is a physical process, unlike what occurs at an active site, which is a chemical process.

36. Answers will vary. A typical response might describe examples of a forensic scientist using knowledge about blood, human tissues, or animal life cycles to solve criminal cases.