8/2/2019 Chapter 2 Section 3Bio Notes

1/2

Chapter 2 Section 31. Many of waters biological functions stem from its chemical structure2. Polar-3. The polar nature of water allows it to dissolve polar substances such as

sugars, ionic compounds, and some proteins

4. Water does not dissolve nonpolar substances, such as oil because aweaker attraction exists between polar and nonpolar molecules thanbetween two polar molecules

5. Dissolved or dissociated ions, are present in all of the aqueous solutionsfound in living things and are important in maintaining normal body

functions

6. The polar nature of water also causes water molecules to be attracted toone and another

7. Hydrogen Bond- is the force of attraction between a hydrogen moleculewith a partial positive charge and another atom or molecule with a partial

or full negative charge

8. Hydrogen bonds in water exert an attractive force string enough so thatwater clings to itself and some other substances

9. Hydrogen bonds form, break and reform with great frequency10.A number or bonds can be bonded together at one time11.Water has the ability to dissolve many substances12.Water molecules stick to each other as a result of hydrogen bonding13.Cohesion- An attractive force that holds molecules of a single substance

together

14.Related to cohesion is the surface tension of the water15.The cohesive forces in the water resulting form hydrogen bonds cause the

molecules at the surface of the water to be pulled downward into the

liquid16.As a result, the water acts as if it has its own skin on its surface17.Adhesion- Is the attractive forces between two particles or different

substances, such as water or gas molecules

18.A related property is, Capillarity- Which is the attraction betweenmolecules that results in the rise of the surface of a liquid when in contact

with a solid

19.Water has a high heat capacity, which means that water can absorb orrelease relatively large amounts of energy in the form of heat with only a

slight change in temperature

20.Energy must be absorbed to break hydrogen bonds and energy isreleased as heat when hydrogen bonds are formed

21.The energy that water initially absorbs breaks hydrogen bonds betweenmolecules

22.Only after these hydrogen bonds are broken does the energy begin toincrease the motion of the water molecules, which raise the temperature

of the water

23.When the temperature of water drops, hydrogen bonds reform, whichreleases large amount of energy in the form of heat

8/2/2019 Chapter 2 Section 3Bio Notes

2/2

24.Therefore, during a hot day, water can absorb a large quantity of energyfrom the sun and can cool the air without a large increase with the

waters temperature

25.As a liquid evaporates, the surface of the liquid that remains behind coolsdown

26.Unlike most solids, which are denser than their liquids, solid water is lessdense then liquid water27.Because ice floats on water, bodies or water such as ponds and lakes

freeze from the top down and not the bottom up

28.A Solution- is a mixture in which one or more substances are uniformlydistributed in another substance

29.Solutions can be mixtures of liquids, gases, solids30.A Solute- is a substance dissolved in the solvent31.The particles that compose a solute may be ions, atoms, or molecules32.The Solvent- is the substance in which the solute is dissolved33.The Concentration- of a solution is the amount of solute dissolved in a

fixed amount of the solution34.A Saturated Solution- is one in which no more solute can be dissolved35.Aqueous Solutions- (solutions in which water is the solvent) are

universally important to all living things

36.One of the most important aspects of a living system is the degree of itsacidity or alkalinity

37.As water molecules move about, they bump into one another, some canresult in a chemical change

38.The first step is that one molecule water molecule pulls apart fromanother water molecule or dissociates into two ions of opposite charges

(see book)

39.Hydroxide ion- OH(negative)40.Hydronium ion- H3O(positive)41.Acid- if the number of hydronium ions in a solution is greater then the

number of hydroxide ions then the solution is acid (see book)

42.These free hydrogen ions combine with water molecules to formhydronium ions, H3O (positive)

43.If sodium hydroxide, NaOH, a solid is dissolved in water, it dissociates toform sodium ions, Na (positive), and hydroxide ions, OH (negative) (see

book)

44.This solution then contains more hydroxide ions then hydronium ionsand is therefore defined as a Base

45.Scientist have developed a scale for comparing the relativeconcentrations of hydronium ions and hydroxide ions in a solution, this

scale is the pH scale, it ranges from 0 to 14

46.The control of pH is important for living systems47.Enzymes can function only within a very narrow pH range48.The control of pH in organisms is often accomplished with buffers49.Buffers- are chemical substances that neutralize small amounts of either

an acid or a base added to a solution