AP Biology : Understanding Essential Properties of Water

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #11 : Ap Biology

Which of the following is not an important characteristic of water in biology?

Possible Answers:

Cohesion

High specific heat

Low boiling point

High density as a liquid, and low density as a solid

Polarity

Correct answer:

Low boiling point

Explanation:

The properties of water make it essential to life. Cohesion refers to its ability to form hydrogen bonds, attracting the molecules together and contributing to its high surface tension. Adhesion refers to water's attractive properties to other substances, and helps processes like absorption through the xylem. Solid ice is less dense than liquid water, allowing life to exist below the frozen surfaces of lakes and ponds. The polarity of water is essential for numerous biological processes and makes it a good solvent for most biological molecules. Finally, the high specific heat of water makes it resistant to temperature change, allowing life forms to maintain relatively constant internal temperatures.

The high specific heat and surface tension of water contribute to its high boiling point, helping to keep it in liquid form for most biological processes.

Example Question #11 : Understanding Essential Properties Of Water

Which property or properties of water is/are most important for water transport in plants?

Possible Answers:

Low density of solid water (ice)

Cohesion and adhesion

Polarity

Universal solvent

High heat capacity

Correct answer:

Cohesion and adhesion

Explanation:

Adhesion refers to the attraction between water molecules and foreign particles or surfaces. Cohesion refers to the attraction between one water molecule and another.

Adhesion of water to the cell walls of the xylem vessels and cohesion of water molecules to one another allow for water transport in plants. This is also known as capillary action.

The high heat capacity, low solid density, and polarity of water, as well as its use as a solvent, are all essential to the role of water in supporting life in other ways.

Example Question #11 : Understanding Essential Properties Of Water

Which of the following properties of water are beneficial to life?

I. High specific heat

II. Evaporative cooling

III. Ice floats in lakes

IV. Dissolves many polar molecules

Possible Answers:

I, II, III, and IV

III and IV

I, II, and IV

II and III

I and IV

Correct answer:

I, II, III, and IV

Explanation:

The high specific heat of water means that it requires a large amount of heat to raise the temperature of water. This helps the temperature of the environment from becoming too hot or too cold. Also, humans are about 66% water, thus this property of water helps us regulate our body temperature too. Evaporative cooling helps prevent bodies from overheating. We have evolved to take advantage of this property of water, perspiring through our skin to cool it down during exercise. The fact that ice floats protects lakes from further cooling by cold wind. The fact that water is such a good solvent for polar molecules allows the chemistry of life to occur. Recall that life uses four main biomolecules, and dehydration synthesis and hydrolysis reactions occur constantly.

Example Question #12 : Understanding Essential Properties Of Water

What is the best definition for osmosis?

Possible Answers:

Active transport of solute particles.

Diffusion of solute particles to a hypotonic region.

Diffusion of water through a selectively permeable membrane.

Diffusion of solute particles to a hypertonic region.

Correct answer:

Diffusion of water through a selectively permeable membrane.

Explanation:

In osmosis, water diffuses through selectively permeable membranes to regions where the concentration of solute is higher (hypertonic).  Osmosis is not the movement of the solute particles.

Example Question #13 : Understanding Essential Properties Of Water

If a cell is dropped into a solution that is hypertonic to the cell, what happens?

Possible Answers:

Water diffuses into the cell.

Water diffuses out of the cell.

No change in diffusion occurs.

The cell has an equilibrium of water in and water out.

Correct answer:

Water diffuses out of the cell.

Explanation:

A hypertonic solution has a higher concentration of solute than the solute in the cell.  Water diffuses to the higher concentration of solute, so water diffuses out of the cell, and the cell shrivels up. One way to think of this is that water follows "salt," as salt is the most common biological solute.

Example Question #14 : Understanding Essential Properties Of Water

If a cell is dropped into a solution that is hypotonic to the cell, what happens?

Possible Answers:

Water diffuses into the cell.

The cell has an equilibrium of water in and water out.

No change in diffusion occurs.

Water diffuses out of the cell.

Correct answer:

Water diffuses into the cell.

Explanation:

When the solution is hypotonic to the cell, the concentration of solute outside the cell is less.  The water diffuses to the higher concentration inside the cell and causes the cell to swell with water, at it may burst. 

Example Question #15 : Understanding Essential Properties Of Water

What type of bonds are formed in the water molecule which contribute to its chemical properties in living systems?

Possible Answers:

Ionic bonds between oxygen and hydrogen

Polar ionic bonds

Nonpolar covalent bonds between oxygen and hydrogen

Polar covalent bonds between oxygen and hydrogen

Correct answer:

Polar covalent bonds between oxygen and hydrogen

Explanation:

The bond between oxygen and hydrogen in water molecules involves the sharing of electrons in which the oxygen atom pulls the electrons towards it more than the hydrogen pulls the electron.  This results in a slight negative charge on the oxygen and a slight positive charge on the hydrogen.  The bond is not ionic because electrons are not totally transferred, rather they are shared.

Example Question #16 : Understanding Essential Properties Of Water

Which of the following would the strongest type of bond present in a sample of water?

Possible Answers:

Ionic bond

Hydrogen bond

Dipole-dipole interactions

Van der Waals interactions

Covalent bond

Correct answer:

Covalent bond

Explanation:

The correct answer is covalent bonds because they are the strongest of all bonds present in a water sample. Although hydrogen bonding is present in water it is not the strongest bond in a sample of water. The bonds that make up the water molecule themselves are strongest. Ionic bonds do not exist in water.

Example Question #17 : Understanding Essential Properties Of Water

What type of bonds in water allow it to engage in cohesion?

Possible Answers:

Ionic bonds

Polar covalent bonds

Hydrogen bonds

Nonpolar covalent bonds

Correct answer:

Hydrogen bonds

Explanation:

Hydrogen bonds are the intermolecular forces that allow it to engage in cohesion.  Ionic bonds are strong bonds within a molecule between a cation and anion.  Polar covalent bonds are bonds within a molecule in which there is a slight charge on the elements.  Nonpolar covalent bonds are bonds within a molecule in which there is no charge on the elements.

Example Question #12 : Understanding Essential Properties Of Water

What is the best description of an acid?

Possible Answers:

A neutral compound that mixes with oil

A compound that takes up  ions.

A compound that releases  ions.

A compound that releases  ions.

Correct answer:

A compound that releases  ions.

Explanation:

Acidic compounds and solutions release hydrogen () ions.  Basic compounds and solutions release  ions and take up hydrogen ions.  Because of their charge acidic compounds and solutions do not mix well with oil, which is nonpolar.

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