Rucete ✏ AP Biology In a Nutshell
1. Water — Practice Questions
This chapter introduces the unique properties of water and how its hydrogen bonding behavior impacts life and biological systems.
(Multiple Choice — Click to Reveal Answer)
1. In a water molecule, hydrogen atoms are attached to oxygen atoms through which type of bond?
(A) hydrogen bond
(B) nonpolar covalent bond
(C) polar covalent bond
(D) ionic bond
Answer
(C) — Oxygen and hydrogen in a water molecule are joined by polar covalent bonds due to the difference in electronegativity.
2. The attraction between the partially positive charge on a hydrogen atom on one water molecule and the partially negative charge on an oxygen atom on another water molecule is called a(n)
(A) hydrogen bond
(B) nonpolar covalent bond
(C) polar covalent bond
(D) ionic bond
Answer
(A) — Hydrogen bonds occur between the hydrogen of one molecule and the oxygen of another.
3. Water’s high specific heat is due to
(A) the lower density of solid ice compared to that of liquid water.
(B) the amount of energy required to break the covalent bonds within a water molecule.
(C) the amount of energy required to break the hydrogen bonds between water molecules.
(D) the low electronegativity of oxygen atoms compared to that of hydrogen atoms.
Answer
(C) — Water’s high specific heat comes from the energy needed to break hydrogen bonds between molecules.
4. Which of the following solutions has the greatest concentration of H+?
(A) stomach acid with a pH of 2
(B) acetic acid with a pH of 3
(C) coffee with a pH of 5
(D) bleach with a pH of 12
Answer
(A) — A lower pH means a higher H+ concentration; pH 2 has the highest among the choices.
5. Solution A has a pH of 4; solution B has a pH of 7. How do the [H+] in these solutions compare?
(A) Solution A has 3 times the [H+] concentration of solution B.
(B) Solution A has 30 times the [H+] concentration of solution B.
(C) Solution A has 1,000 times the [H+] concentration of solution B.
(D) Solution A has 3,000 times the [H+] concentration of solution B.
Answer
(C) — The pH scale is logarithmic; a 3-unit difference equals a 1000x difference in H+ concentration.
6. Coastal areas near large bodies of water tend to have more stable climates than inland areas at the same latitude. Which of the following is the property of water that best explains this difference in climate?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(B) — Water’s high specific heat helps moderate temperatures near large bodies of water.
7. Small, lightweight insects can walk on the surface of water. Which of the following is the property of water that best explains this phenomenon?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(A) — High surface tension, due to hydrogen bonding, allows insects to walk on water.
8. Arctic seals and walruses rely on ice floes for survival. Which of the following best explains why these ice floes exist?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(D) — Ice is less dense than liquid water, so it floats, creating ice floes.
9. Redwood trees can move water upward from their roots to other parts of the tree. Which of the following properties of water best explains this?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(C) — Capillary action helps water rise in narrow xylem tubes in tall trees.
10. In hot weather, humans can cool their body temperature by sweating. Which of the following properties of water makes this possible?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(B) — Water's high specific heat allows it to absorb heat during evaporation, cooling the body.
11. Which of the following properties allows water to climb the xylem of plants against gravity?
(A) high surface tension
(B) high specific heat
(C) capillary action
(D) density of ice
Answer
(C) — Capillary action, a result of cohesion and adhesion, allows water to move upward in narrow plant vessels.
12. What type of bond is responsible for water’s cohesive properties?
(A) ionic bond
(B) hydrogen bond
(C) polar covalent bond
(D) peptide bond
Answer
(B) — Hydrogen bonds between water molecules cause them to stick together, creating cohesion.
13. Why does ice float on liquid water?
(A) Ice has more hydrogen bonds
(B) Ice is denser than water
(C) Hydrogen bonds expand the structure of ice
(D) Water has lower surface tension when frozen
Answer
(C) — Hydrogen bonds in ice hold molecules apart in a crystalline structure, making it less dense than water.
14. Which of the following best explains why salt (NaCl) dissolves in water?
(A) Water is nonpolar
(B) Salt is nonpolar
(C) Water forms hydration shells around ions
(D) Salt forms covalent bonds with water
Answer
(C) — Polar water molecules surround and separate Na⁺ and Cl⁻ ions, forming hydration shells.
15. Which part of the water molecule has a partial negative charge?
(A) Hydrogen atom
(B) Oxygen atom
(C) The bond between hydrogen and oxygen
(D) None, water is nonpolar
Answer
(B) — Oxygen has a higher electronegativity, causing electrons to spend more time around it.
16. What makes water an effective temperature buffer in organisms?
(A) Low specific heat
(B) High density
(C) High specific heat
(D) High surface tension
Answer
(C) — Water’s high specific heat resists temperature changes, stabilizing internal and environmental conditions.
17. Which type of molecule dissolves best in water?
(A) Nonpolar molecules
(B) Lipids
(C) Polar molecules
(D) Hydrocarbons
Answer
(C) — Water is polar, so it best dissolves other polar molecules and ionic compounds.
18. A solution has a pH of 2. How would you classify it?
(A) Weakly basic
(B) Neutral
(C) Weakly acidic
(D) Strongly acidic
Answer
(D) — A pH of 2 indicates a high concentration of H⁺, which makes the solution strongly acidic.
19. What property of water allows it to moderate Earth’s climate?
(A) Cohesion
(B) High specific heat
(C) Capillary action
(D) High surface tension
Answer
(B) — High specific heat allows water to absorb and release large amounts of heat without drastic temperature change.
20. Which of the following is true about pH?
(A) Higher pH means higher H+ concentration
(B) Lower pH means lower H+ concentration
(C) pH 7 is acidic
(D) Lower pH means higher H+ concentration
Answer
(D) — The pH scale is inverse to [H⁺]; a lower pH indicates a higher concentration of hydrogen ions.
21. Water's ability to stabilize temperature in organisms and environments is mainly due to:
(A) Adhesion
(B) Cohesion
(C) Surface tension
(D) High specific heat
Answer
(D) — High specific heat makes water a great temperature stabilizer.
22. What gives water molecules their polarity?
(A) Symmetrical electron sharing
(B) Equal electronegativity
(C) Unequal sharing of electrons
(D) Lack of hydrogen bonds
Answer
(C) — Oxygen and hydrogen have unequal electronegativity, leading to partial charges and molecular polarity.
23. Which part of a water molecule is attracted to a chloride ion (Cl⁻)?
(A) Hydrogen
(B) Oxygen
(C) Both equally
(D) Neither
Answer
(A) — The partially positive hydrogen atoms in water are attracted to negatively charged ions like Cl⁻.
24. What happens when water freezes?
(A) It becomes more dense
(B) It contracts
(C) Hydrogen bonds form a lattice structure
(D) It releases hydrogen ions
Answer
(C) — Water molecules form a lattice held by hydrogen bonds, creating less density than liquid water.
25. What makes water a good solvent for salts and sugars?
(A) It is nonpolar
(B) It forms covalent bonds with solutes
(C) It forms hydrogen bonds with nonpolar molecules
(D) It is polar and interacts with charged and polar solutes
Answer
(D) — Water’s polarity allows it to surround and interact with ionic and polar substances, dissolving them effectively.
26. Which property of water allows it to form hydration shells around ions like Na+ and Cl⁻?
(A) Water’s high specific heat
(B) Water’s polarity
(C) Water’s surface tension
(D) Water’s nonpolarity
Answer
(B) — Water’s polarity enables it to surround charged ions, forming hydration shells.
27. What would happen if ice were denser than liquid water?
(A) Ice would float
(B) Ice would sink, possibly freezing aquatic ecosystems solid
(C) It would not affect aquatic life
(D) Water would no longer be polar
Answer
(B) — If ice sank, entire bodies of water could freeze solid, endangering aquatic organisms in winter.
28. Which of the following best explains why evaporation of sweat cools the body?
(A) It increases internal heat
(B) It adds water to the skin
(C) It removes heat energy as hydrogen bonds break
(D) It traps heat in water vapor
Answer
(C) — Evaporation requires breaking hydrogen bonds, which absorbs body heat and cools the skin.
29. Which of the following would have the highest concentration of hydrogen ions (H⁺)?
(A) A solution with a pH of 7
(B) A solution with a pH of 2
(C) A solution with a pH of 6
(D) A solution with a pH of 9
Answer
(B) — Lower pH values indicate higher H⁺ concentrations; pH 2 is the most acidic.
30. Why do ionic compounds dissolve more readily in water than in nonpolar solvents?
(A) Water forms covalent bonds with ions
(B) Water is nonpolar and repels ions
(C) Polar water molecules stabilize ions via electrostatic interactions
(D) Nonpolar solvents attract ions more strongly
Answer
(C) — Water stabilizes ions by surrounding them with polar molecules that interact electrostatically.
31. How does water help buffer temperature changes in cells?
(A) It instantly changes temperature with its surroundings
(B) It has a low boiling point
(C) Its high specific heat resists rapid changes in temperature
(D) It dissolves heat energy
Answer
(C) — Water’s high specific heat allows it to absorb or release heat slowly, stabilizing temperature.
32. A solution has 100 times more H⁺ ions than another. How much lower is its pH?
(A) 1 unit
(B) 2 units
(C) 10 units
(D) 100 units
Answer
(B) — Each pH unit represents a 10-fold change in [H⁺]; 100 times means 2 pH units lower.
33. What explains water’s ability to stick to the sides of glass tubes?
(A) Cohesion
(B) Adhesion
(C) Surface tension
(D) Specific heat
Answer
(B) — Adhesion is the attraction between water molecules and other materials like glass.
34. Which of the following is a result of hydrogen bonding in water?
(A) Water molecules repel each other
(B) Water has a low boiling point
(C) Water has high surface tension and cohesion
(D) Water acts as a poor solvent
Answer
(C) — Hydrogen bonding leads to high cohesion, surface tension, and other key water properties.
35. A student predicts that salt will dissolve better in water than in oil. Why is this correct?
(A) Oil is polar and dissolves ionic compounds
(B) Water is nonpolar and cannot dissolve salt
(C) Salt is nonpolar and interacts better with water
(D) Water is polar and interacts with ionic compounds
Answer
(D) — Water is polar, which allows it to surround and dissolve charged ions like Na⁺ and Cl⁻ from salt.
36. Describe the property of water that allows misters to have an effective cooling effect at outdoor events.
Answer
Water’s high heat of vaporization — The hydrogen bonds between water molecules require significant energy to break, so water absorbs heat from the body as it evaporates, resulting in cooling.
37. Explain why the evaporation of water makes the participants in these events more comfortable.
Answer
Evaporation absorbs heat — As water evaporates, it absorbs heat from the skin to break hydrogen bonds, lowering the body temperature.
38. Predict whether nonpolar oil would have the same cooling effect on skin as water.
Answer
Less effective cooling effect — Nonpolar molecules don’t form hydrogen bonds and require less energy to evaporate, so they absorb less body heat during evaporation.
39. Justify your prediction from question 38 using water’s molecular properties.
Answer
Water forms hydrogen bonds, oil does not — Water's hydrogen bonds require more energy to break, allowing it to remove more heat from the body during evaporation.
40. Describe the type of bond formed between water molecules.
Answer
Hydrogen bonds — These bonds form due to the attraction between partially positive hydrogen and partially negative oxygen atoms of different water molecules.
41. Explain why hydrogen bonds form between water molecules.
Answer
Due to polarity — Water has partial charges caused by uneven electron sharing; this leads to electrostatic attraction between molecules.
42. Would an ionic salt dissolve more readily in water or methane? Explain your answer.
Answer
Water — Water is polar and can surround ions with hydration shells; methane is nonpolar and cannot interact with ions effectively.
43. Support the claim that a waxy, nonpolar cuticle on leaves reduces water loss.
Answer
Nonpolar barrier — The cuticle prevents polar water molecules from escaping, minimizing evaporation through the leaf surface.
44. Explain why tubes B, C, and D in the experiment had lower pH after 20 minutes.
Answer
CO₂ from respiration formed carbonic acid — Carbon dioxide from snails dissolved in water, forming carbonic acid and increasing H⁺ concentration, lowering the pH.
45. Identify the independent and dependent variables in the aquatic snail experiment.
Answer
Independent: number of snails
Dependent: pH of water
46. Identify the tube that had 100 times as many H⁺ ions as tube A, and explain why.
Answer
Tube C — A 2 pH unit drop (from 7 to 5) corresponds to a 100x increase in H⁺ ion concentration on the logarithmic pH scale.
47. Predict the effect of adding Elodea to all tubes at the start of the experiment.
Answer
pH would increase or decrease less — Elodea would absorb CO₂ through photosynthesis, reducing carbonic acid and thus increasing pH or limiting its drop.
48. Justify your prediction in question 47.
Answer
Photosynthesis removes CO₂ — Less CO₂ means less carbonic acid formation, so fewer H⁺ ions are released, maintaining a higher pH.
49. Explain how buffers maintain pH stability in biological systems.
Answer
By neutralizing excess acids or bases — Buffers like the carbonic acid–bicarbonate system shift reactions to counteract pH changes.
50. Describe the importance of water’s polarity to biological systems.
Answer
It enables hydrogen bonding, solubility, and temperature regulation — Water’s polarity supports life by facilitating interactions with ions and molecules, stabilizing temperature, and enabling capillary action.