1. Water and the Fitness of the Environment
Chapter 3
Water and the Fitness of the Environment

2. Overview: The Molecule That Supports All of Life
All living organisms require water more than any other substance
Most cells are surrounded by water, and cells themselves are about 70-95% water
The abundance of water is the main reason the Earth is habitable

3. Concept 3.1: The polarity of water molecules results in hydrogen bonding
The water molecule is a polar molecule: The opposite ends have opposite charges
Polarity allows water molecules to form hydrogen bonds with each other

4. Concept 3.2: Four emergent properties of water contribute to Earth’s fitness for life
Four of water’s properties that facilitate an environment for life:
Cohesive behavior
Ability to moderate temperature
Expansion upon freezing
Versatility as a solvent

5. Cohesion
Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion
Cohesion helps the transport of water against gravity in plants
Adhesion of water to plant cell walls also helps to counter gravity

6. Water’s High Specific Heat
The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC
Water’s high specific heat minimizes temperature fluctuations to within limits that permit life
Heat is absorbed when hydrogen bonds break
Heat is released when hydrogen bonds form

7. Water is an effective solvent because it readily forms hydrogen bonds
Water is the universal solvent – it dissolves more substances than anything - including HCl! Ex: sugar, salt, dye, honey etc.. Water surrounds and attracts ions and other polar charges.

8. Hydrophilic and Hydrophobic Substances
A hydrophilic substance is one that has an affinity for water
A hydrophobic substance is one that does not have an affinity for water
Ice is less dense than water – important for insulating aquatic life!!

9. Water dissociates to form acids and bases:
Hydronium
ion (H3O+)
Hydroxide
ion (OH–)

10. Acids and Bases
An acid is any substance that increases the H+ concentration of a solution
A base is any substance that reduces the H+ concentration of a solution

11. LE 3-8 pH Scale 1 Battery acid 2 Digestive (stomach)1
Battery acid 2
Digestive (stomach)
juice, lemon juice
Increasingly Acidic
[H+] > [OH–] 3
Vinegar, beer, wine,
cola 4
Tomato juice 5
Black coffee
Rainwater 6
Urine
Neutral
[H+] = [OH–] 7
Pure water
Human blood 8
Seawater 9 10
Increasingly Basic
[H+] < [OH–]
Milk of magnesia 11
Household ammonia 12
Household bleach 13
Oven cleaner 14

12. Buffers The internal pH of most living cells must remain close to pH 7
Buffers are substances that minimize changes in concentrations of H+ and OH- in a solution
Most buffers consist of an acid-base pair that reversibly combines with H+

13. More acidic 1 2 3 Acid rain 4 5 Normal rain 6 7 8 9 10 11 12 13 More
LE 3-9
More
acidic 1 2 3
Acid
rain 4 5
Normal
rain 6 7 8 9 10 11 12 13
More
basic 14

14. Do one brave thing today…then run like hell!
Any Questions?
Do one brave thing today…then run like hell!

15. A. The following are pH values: cola-2; orange juice-3; beer-4; coffee-5; human blood-7.4. Which of these liquids has the highest molar concentration of OH-?
cola
orange juice
beer
coffee
human blood
Answer: e
Source: Taylor - Student Study Guide for Biology, Sixth Edition, Test Your Knowledge Question #18

16. C. If the pH of a solution is increased from pH 8 to pH 9, it means that the
concentration of H+ is 10 times greater than what it was at pH 8.
concentration of H+ is 100 times less than what it was at pH 8.
concentration of OH- is 10 times greater than what it was at pH 8.
concentration of OH- is 100 times less than what it was at pH 8.
concentration of H+ is greater and the concentration of OH- is less than at pH 8.
Answer: c
Source: Barstow - Test Bank for Biology, Sixth Edition, Question #43

17. D. Acid precipitation has lowered the pH of a particular lake to 4
D. Acid precipitation has lowered the pH of a particular lake to 4.0. What is the hydroxide ion concentration of the lake?
10-7 M
10-4 M
10-10 M
10-14 M
10 M
Answer: c
Source: Campbell/Reece - Biology, Sixth Edition, EOC Self-Quiz Question #10
Discussion Notes for the Instructor
To answer this question students need to know the relationship between pH and hydroxide concentration.