Question 1

Which property of water is primarily responsible for its ability to dissolve ionic compounds such as NaCl?

Accepted Answer

Its high dielectric constant $$\left( \varepsilon \approx 80 \right)$$

Question 2

Why does ice float on liquid water?

Accepted Answer

Ice has a lower density than liquid water because its hydrogen bonds form an open tetrahedral lattice.

Question 3

Which of the following best explains why water has a much higher boiling point than other molecules of similar molecular weight, such as $$\mathrm{NH_3$}$$ and $$\mathrm{CH_4$}$$?

Accepted Answer

Water forms extensive hydrogen bonds, requiring more energy to break.

Question 4

A patient with central diabetes insipidus is unable to concentrate urine. Which molecular defect is most likely responsible for this condition?

Accepted Answer

Defective aquaporin-2 channels in the nephron membrane

Question 5

Which of the following statements about hydrogen bonding in water is correct?

Accepted Answer

Each water molecule can act as both a hydrogen bond donor and acceptor, forming up to four hydrogen bonds.

Question 6

Which property of water allows it to buffer against sudden temperature changes in living systems?

Accepted Answer

High heat capacity $$\left( c = 4187 \ \mathrm{J/kg\cdot ^\circ C} \right)$$

Question 7

What is the primary reason that water is an excellent solvent for polar and ionic substances?

Accepted Answer

Water has a high dielectric constant and forms hydration shells around ions.

Question 8

Which of the following best describes the entropy change when two hydrophobic molecules aggregate in water?

Accepted Answer

Entropy of the solvent increases as water molecules are released from clathrate cages.

Question 9

Which of the following is a direct consequence of water’s high surface tension in biological systems?

Accepted Answer

Allows small insects to walk on water surfaces

Question 10

A protein is denatured in water, disrupting its internal hydrogen bonds. What is the most likely interaction that replaces these internal bonds?

Accepted Answer

Hydrogen bonds between water and the protein’s polar groups

Question 11

Which of the following best explains why water can pass through the lipid bilayer of cells despite being polar?

Accepted Answer

Water passes through specialized channel proteins called aquaporins.

Question 12

Which property of water is most important for maintaining a stable internal environment (homeostasis) in living organisms?

Accepted Answer

High specific heat capacity

Question 13

Which of the following best describes the molecular geometry of a water molecule?

Accepted Answer

Bent, with a bond angle of $$104.5^\circ$$

Question 14

Which of the following is a consequence if ice were more dense than liquid water?

Accepted Answer

Ice would sink, causing bodies of water to freeze from the bottom up.

Question 15

Which of the following best explains why water has a high heat of vaporization?

Accepted Answer

Extensive hydrogen bonding must be overcome to convert liquid water to vapor.

Question 16

Which of the following statements about the role of vasopressin (antidiuretic hormone, ADH) in water reabsorption in the kidneys is correct?

Accepted Answer

Vasopressin increases water reabsorption by increasing the number of aquaporin-2 channels in the nephron membrane.

Question 17

Which of the following best describes the interaction between water and nonionic polar compounds?

Accepted Answer

Hydrogen bonding or dipole-dipole interactions

Question 18

What is the effect of water forming clathrate structures around hydrophobic molecules?

Accepted Answer

It decreases the entropy of the solvent, which is thermodynamically unfavorable.

Question 19

Which property of water is most responsible for its ability to stabilize the structures of proteins and nucleic acids?

Accepted Answer

Ability to form multiple hydrogen bonds

Question 20

Which of the following best explains why water is a poor solvent for nonpolar molecules?

Accepted Answer

Water cannot form favorable interactions with nonpolar molecules, leading to aggregation of hydrophobic substances.

The Role of Water in Living Systems

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