1

Water and the Fitness of

the Environment

2

Importance of water

• Overview: The Molecule That Supports All of Life

• Water is the biological medium here on Earth

• All living organisms require water more than any other substance

3

Water Facts

• The polarity of water molecules results in hydrogen bonding

• The water molecule is a polar molecule

4

Water’s Polarity• The polarity of water molecules

– Allows them to form hydrogen bonds with each other

– Contributes to the various properties water exhibits

Hydrogenbonds

+

+

H

H+

+

–

–

– –

Figure 3.2

5

Properties of water

• Four emergent properties of water contribute to Earth’s

fitness for life

1. Cohesion - Like molecules bonding to each other (water

attracting other water molecules)

Water conducting

cells

2. Surface tensionIs a measure of how hard it is to break the

surface of a liquid

3. Water moderates air temperature because it has a high specific heat, which allows

it to minimize temperature fluctuations to within limits that

permit life

4. Water is a versatile solvent due to its polarity

6

Insulation of Bodies of Water by Floating Ice

• Solid water, or ice– Is less dense than liquid water– Floats in liquid water

Life can exist under the frozen surfaces of lakes and polar seas

7

• The different regions of the polar water molecule can interact with ionic compounds called solutes and dissolve themNegative

oxygen regions

of polar water

molecules are

attracted to sodium

cations (Na+).

+

+

+

+Cl –

–

–

–

–

Na+Positive hydrogen regions

of water molecules cling to chloride anions

(Cl–).

++

+

+

–

–

–

–

–

–Na+

Cl–

Figure 3.6

8

Hydrophilic and Hydrophobic Substances

• A hydrophobic substance– Does not have an affinity for water

• A hydrophilic substance– Has an affinity for water

9

Acids and Bases

• Dissociation of water molecules leads to acidic and basic conditions that affect living organisms

• Organisms must maintain homeostasis in the pH of their internal and external environments

10

• Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions

• Changes in the concentration of these ions Can have a great affect on pH in living organisms

H

Hydroniumion (H3O+)

H

Hydroxideion (OH–)

H

H

H

H

H

H

+ –

+

Figure on p. 53 of water dissociating

Effects of Changes in pH

11

Acids and Bases

• An acid– Is any substance that increases the

hydrogen ion concentration of a solution• A base

– Is any substance that reduces the hydrogen ion concentration of a solution

12

The pH Scale• Scale goes from 0-14 with 7 neutral• The pH of a solution Is determined by the

relative concentration of hydrogen ions

• Difference of 10X in hydrogen ion concentration between any two pH values

• Acids have a higher number of H+ ions than a base

• Acids produce H+ ion in solution• Bases produce OH- ions in solution

13

The pH scale and pH values of various aqueous solutions

Incr

easi

ngly

Aci

dic

[H+]

> [

OH

–]

Incr

easi

ngly

Bas

ic[H

+]

< [

OH

–]

Neutral[H+] = [OH–]

Oven cleaner

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

pH Scale

Battery acid

Digestive (stomach) juice, lemon juiceVinegar, beer, wine,colaTomato juice

Black coffee RainwaterUrine

Pure waterHuman blood

Seawater

Milk of magnesia

Household ammonia

Household bleach

Figure 3.8

14

Buffers

• The internal pH of most living cells– Must remain close to pH 7

• Buffers– Are substances that minimize changes

in the concentrations of hydrogen and hydroxide ions in a solution

– Consist of an acid-base pair that reversibly combines with hydrogen ions

– Made by organisms

15

• Acid precipitation– Can damage life in Earth’s ecosystems

0

12

34

56

78

910

11

12

1314

Moreacidic

Acidrain

Normalrain

Morebasic

Figure 3.9

16

Moles and Molarity

• A mole– Represents an exact number of

molecules of a substance in a given mass

• Molarity– Is the number of moles of solute per liter

of solution

17

1 In the beginning God created the heavens and the earth.  2 Now the earth was formless and empty, darkness was over the surface of the deep, and the Spirit of God was hovering over the waters.

God created water before life