Water ✏ AP Biology Practice Questions 2

Rucete ✏ AP Biology In a Nutshell

1. Water — Practice Questions 2


This chapter explores water's essential roles in life, focusing on polarity, hydrogen bonding, and how they influence biological functions.

(Multiple Choice — Click to Reveal Answer)

1. Which property allows water molecules to stick to each other?
(A) Adhesion
(B) Cohesion
(C) Surface tension
(D) Solubility

Answer

(B) — Cohesion refers to the attraction between like molecules, such as water to water via hydrogen bonding.

2. Which part of the water molecule has a partial positive charge?
(A) Oxygen atom
(B) Hydrogen atom
(C) Both oxygen and hydrogen
(D) Neither

Answer

(B) — The hydrogen atoms in water have partial positive charges due to unequal electron sharing with oxygen.

3. What characteristic of water helps insects like water striders stay on its surface?
(A) Capillary action
(B) High specific heat
(C) Surface tension
(D) Solubility

Answer

(C) — Surface tension, due to hydrogen bonding, creates a "skin" on the surface strong enough to support small insects.

4. What allows water to move up a thin tube against gravity?
(A) Adhesion and cohesion
(B) Surface tension
(C) High heat capacity
(D) Vapor pressure

Answer

(A) — Capillary action results from water's adhesive interaction with the tube and cohesive interactions with itself.

5. Which of the following best describes the role of buffers in living systems?
(A) They produce water when pH changes
(B) They prevent water from ionizing
(C) They resist changes in pH
(D) They convert acids into proteins

Answer

(C) — Buffers maintain stable internal pH by absorbing excess H⁺ or OH⁻.

6. What makes water a good solvent for salt?
(A) It is nonpolar
(B) It is neutral in pH
(C) It is polar and surrounds charged particles
(D) It evaporates easily

Answer

(C) — Water’s polarity allows it to interact with and dissolve ionic compounds by surrounding their charged ions.

7. Why is water's high specific heat important to life?
(A) It helps water evaporate quickly
(B) It prevents water from dissolving too much
(C) It stabilizes temperature in organisms and environments
(D) It increases density of ice

Answer

(C) — High specific heat helps regulate temperature changes, protecting cells and ecosystems from extreme shifts.

8. What causes water to expand when it freezes?
(A) Oxygen’s high electronegativity
(B) Formation of covalent bonds
(C) Hydrogen bonds arranging molecules into a lattice
(D) Water’s pH dropping below 7

Answer

(C) — Hydrogen bonding locks molecules in a hexagonal structure that occupies more space than in liquid form.

9. Which condition describes a solution with a pH of 8?
(A) Strong acid
(B) Weak acid
(C) Weak base
(D) Strong base

Answer

(C) — A pH above 7 indicates a basic solution; 8 is only slightly basic, thus a weak base.

10. What would happen to a freshwater fish placed in a saltwater tank?
(A) It would gain water and swell
(B) It would lose water and dehydrate
(C) It would maintain homeostasis
(D) It would stop breathing

Answer

(B) — Water would move out of the fish's cells by osmosis into the saltier environment, causing dehydration.

11. Water is described as a polar molecule. What does this mean?
(A) Water contains ions
(B) Oxygen and hydrogen share electrons equally
(C) There is an uneven distribution of electron density
(D) Water evaporates easily

Answer

(C) — Polar molecules have regions of partial positive and negative charge due to unequal electron sharing.

12. What is the result of hydrogen bonding in water?
(A) High vapor pressure
(B) High boiling point
(C) Low freezing point
(D) Weak surface tension

Answer

(B) — Hydrogen bonding requires more energy to break, raising water’s boiling point.

13. What property helps maintain stable ocean temperatures?
(A) Low pH
(B) High specific heat
(C) Low boiling point
(D) High surface tension

Answer

(B) — The ocean’s temperature is stabilized by water’s ability to absorb and release heat slowly.

14. What type of bond holds the atoms within a single water molecule together?
(A) Hydrogen bond
(B) Ionic bond
(C) Nonpolar covalent bond
(D) Polar covalent bond

Answer

(D) — The oxygen and hydrogen atoms in a water molecule are held together by polar covalent bonds.

15. Which of the following explains why salt dissolves but oil does not in water?
(A) Oil is too dense
(B) Salt is polar; oil is nonpolar
(C) Salt is nonpolar; oil is polar
(D) Oil forms hydrogen bonds with water

Answer

(B) — Water dissolves polar or charged substances like salt, but not nonpolar molecules like oil.

16. What happens to hydrogen bonds when water evaporates?
(A) They form more easily
(B) They stay intact
(C) They must be broken
(D) They strengthen

Answer

(C) — Evaporation requires energy to break hydrogen bonds, allowing water molecules to escape as vapor.

17. What makes ice beneficial to aquatic life during winter?
(A) Ice insulates the water below
(B) Ice conducts cold into the water
(C) Ice absorbs all the oxygen
(D) Ice blocks all sunlight

Answer

(A) — Since ice floats and insulates, it helps prevent the water below from freezing completely, protecting life.

18. What would you expect if the hydrogen bonds in water were significantly weaker?
(A) Water would boil at a higher temperature
(B) Water would no longer be polar
(C) Water would freeze at a higher temperature
(D) Water would evaporate more easily

Answer

(D) — Weaker hydrogen bonds mean less energy needed for evaporation, so water would vaporize more readily.

19. A student mixes salt into water and stirs until it disappears. What is the best term for this mixture?
(A) Suspension
(B) Colloid
(C) Solution
(D) Compound

Answer

(C) — A solution is a homogeneous mixture where solutes like salt are evenly dissolved in the solvent, water.

20. Which substance would most likely increase the pH of a solution?
(A) Vinegar
(B) Sodium hydroxide
(C) Lemon juice
(D) Carbonic acid

Answer

(B) — Sodium hydroxide is a strong base and would raise the pH by decreasing H⁺ concentration.

21. Why is water considered the "universal solvent"?
(A) It dissolves gases like oxygen
(B) It dissolves more substances than any other liquid
(C) It evaporates quickly
(D) It forms covalent bonds with everything

Answer

(B) — Water dissolves a wide variety of polar and ionic substances due to its polarity.

22. Why do coastal areas typically have milder climates than inland areas?
(A) Ice forms more readily near coasts
(B) Water has low heat of vaporization
(C) Oceans have high specific heat and buffer temperature
(D) Sea breezes prevent evaporation

Answer

(C) — The high specific heat of water allows it to absorb and release heat slowly, stabilizing climate.

23. What is the charge distribution in a water molecule?
(A) Neutral overall with no partial charges
(B) Negative on hydrogen, positive on oxygen
(C) Positive on hydrogen, negative on oxygen
(D) Equally charged throughout

Answer

(C) — Water is polar, with a partial positive charge on the hydrogens and a partial negative charge on the oxygen.

24. Which process removes heat from the body through evaporation?
(A) Condensation
(B) Sweating
(C) Freezing
(D) Shivering

Answer

(B) — Sweating relies on water’s heat of vaporization to remove body heat through evaporation.

25. What property of water makes it essential for nutrient transport in organisms?
(A) It’s nonpolar
(B) It’s a good solvent
(C) It’s highly acidic
(D) It’s stable in gas form

Answer

(B) — Water dissolves many nutrients, allowing them to be carried in solution throughout an organism.

26. Why does water have a relatively high boiling point compared to other small molecules?
(A) Because of ionic bonds between molecules
(B) Due to its low molecular weight
(C) Due to hydrogen bonding between molecules
(D) Because water is nonpolar

Answer

(C) — Hydrogen bonds between water molecules require more energy to break, increasing the boiling point.

27. Which of the following explains how water supports temperature regulation in cells?
(A) It easily conducts heat
(B) It resists temperature change due to high specific heat
(C) It quickly changes phase
(D) It doesn’t interact with other molecules

Answer

(B) — Water’s high specific heat buffers temperature changes in cells, protecting biochemical processes.

28. Why is water's density maximum at 4°C and not at freezing point?
(A) Water starts to evaporate at 0°C
(B) Hydrogen bonds are strongest at 4°C
(C) Ice formation expands molecules
(D) Covalent bonds stretch in cold

Answer

(C) — Below 4°C, water molecules begin arranging into a solid lattice (ice) with more space between them, lowering density.

29. Which property of water most directly affects enzyme activity in cells?
(A) High vapor pressure
(B) pH stability via buffering systems
(C) Ability to form ice
(D) Capillary action

Answer

(B) — Water-based buffers help maintain constant pH levels essential for proper enzyme function.

30. What would be the effect of significantly decreasing the polarity of water molecules?
(A) Water would boil at a higher temperature
(B) Water would dissolve more nonpolar molecules
(C) Hydrogen bonding would be reduced
(D) Water would become more cohesive

Answer

(C) — Less polarity would mean weaker or fewer hydrogen bonds, impacting water’s unique properties.

31. How does the structure of water make it effective at dissolving ionic compounds?
(A) It breaks covalent bonds in the solute
(B) It reduces temperature
(C) Its partial charges interact with ions
(D) It has no effect on ionic compounds

Answer

(C) — The partial charges in polar water molecules stabilize ions by surrounding them, forming hydration shells.

32. A scientist increases the amount of H⁺ ions in a water sample. What happens to its pH?
(A) It increases
(B) It remains the same
(C) It decreases
(D) It fluctuates randomly

Answer

(C) — pH is inversely related to H⁺ concentration; adding H⁺ lowers the pH.

33. In a biological experiment, what explains the reduced water loss from leaves coated with a waxy cuticle?
(A) Water is absorbed through wax
(B) Polar water can’t pass nonpolar layers
(C) Wax increases photosynthesis
(D) Cuticle causes more condensation

Answer

(B) — The waxy, nonpolar cuticle prevents polar water molecules from escaping easily, reducing evaporation.

34. Why do aquatic organisms survive under frozen lakes in winter?
(A) Water becomes warmer as it freezes
(B) Fish develop antifreeze proteins
(C) Ice floats and insulates the water below
(D) Ice melts from the bottom

Answer

(C) — Ice floats due to lower density, forming an insulating layer that prevents deeper water from freezing.

35. Which statement accurately compares cohesion and adhesion in water?
(A) Cohesion attracts water to surfaces; adhesion binds water to itself
(B) Adhesion and cohesion are the same process
(C) Cohesion binds water molecules; adhesion binds water to other substances
(D) Cohesion breaks hydrogen bonds; adhesion forms covalent bonds

Answer

(C) — Cohesion is the attraction between water molecules; adhesion is the attraction between water and other materials.

36. Explain why water is considered a polar molecule.

Answer

Water has partial charges — Oxygen pulls electrons more strongly than hydrogen, creating a partial negative charge on oxygen and partial positives on hydrogen.

37. Describe how hydrogen bonds contribute to water’s high surface tension.

Answer

Hydrogen bonds hold surface molecules tightly — Molecules at the surface form stronger interactions, creating a "skin-like" effect.

38. What property of water allows it to climb up plant stems?

Answer

Capillary action — Cohesion (water to water) and adhesion (water to xylem) pull water upward through narrow tubes.

39. Explain how water stabilizes internal temperatures in organisms.

Answer

High specific heat — Water absorbs heat with little temperature change, buffering cells from rapid fluctuations.

40. Why does ice float on water?

Answer

Ice is less dense — Hydrogen bonds in ice create an open lattice structure, making it less dense than liquid water.

41. What happens to hydrogen bonds when water freezes?

Answer

They become fixed — Water molecules form stable hydrogen bonds in a crystalline structure.

42. How does sweating help cool the human body?

Answer

Evaporation absorbs heat — Breaking hydrogen bonds during evaporation draws heat from the skin.

43. Why is water a good solvent for biological molecules?

Answer

Water is polar — Its partial charges interact with and dissolve polar molecules and ions.

44. What is the role of buffers in water-based biological fluids?

Answer

Stabilize pH — Buffers resist pH changes by accepting or releasing hydrogen ions.

45. Describe what happens when carbon dioxide dissolves in water in terms of pH.

Answer

pH decreases — CO₂ forms carbonic acid, releasing H⁺ and lowering pH.

46. Why is a logarithmic scale used for pH?

Answer

To express large differences in [H⁺] — Each unit change equals a tenfold change in hydrogen ion concentration.

47. How does water’s polarity affect ion dissociation?

Answer

Water surrounds ions — Polar water molecules stabilize and separate ions into solution.

48. A solution has a pH of 3. How much more acidic is it than one with pH 6?

Answer

1000 times more acidic — A 3-unit decrease on the pH scale corresponds to a 10³ (1000x) increase in [H⁺].

49. How does the waxy cuticle of plants help reduce water loss?

Answer

Nonpolar barrier — The cuticle prevents polar water from escaping through evaporation.

50. Why can’t oil dissolve in water?

Answer

Oil is nonpolar — Water only dissolves polar or charged substances, and cannot interact with nonpolar molecules like oil.

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