biol 101 chp 3: water and life

BIOL 101 General Biology I

Chapter 3

Water & the Fitness of the Environment

Rob Swatski Associate Professor of Biology

HACC – York Campus 1

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Water: The Molecule That Supports All of Life

• Water is the biological medium on Earth

• 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

Water = Life

4

Surface of Mars Surface of Earth

5

Water = Polar molecule

N

S

+

-

6

–

H

+

H

O

+

+

+

–

–

– Hydrogen bond

7

Properties of Water

How do they benefit living things? 8

Emergent Properties of Water

Cohesion Moderates

temperature Expands

when frozen Versatile solvent

9

10

Cohesion

How?

Water-conducting cells

Adhesion

Cohesion

150 µm

Direction of water movement

11

12

Surface Tension

How?

13

14

Moderates Temperature

15

Moderation of Temperature by Water

• Water absorbs heat from warmer air and releases stored heat to cooler air

• Water can absorb or release a large amount of heat with only a slight change in its own temperature

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17

Energy & Water

Potential

Kinetic

Heat

Temperature

Metric System Units - Energy

Celsius calorie

(cal)

kilocalorie (kcal or Calorie)

joule

1j = 0.239 cal

1 cal = 4.184 j

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Specific Heat

1 cal/g/ºC

So what…?

HEAT +/- 1 g 1ºC

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• Water’s high specific heat can be traced to hydrogen bonding

– Heat is absorbed when hydrogen bonds break

– Heat is released when hydrogen bonds form

• The high specific heat of water minimizes temperature fluctuations to within limits that permit life

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–

H

+

H

O

+

+

+

–

–

– Hydrogen bond

21

22

Heat Heat

What happens to the bond?

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Heat Heat

What happens to the bond?

Santa Barbara 73°

Los Angeles

(Airport) 75°

Pacific Ocean 68°

Santa Ana 84°

Burbank 90°

San Bernardino 100°

Palm Springs 106°

Riverside 96°

San Diego 72° 40 miles

70s (°F)

80s

90s

100s

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26

27

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Evaporation

Heat of evaporation

Evaporative cooling

Helps stabilize

temperatures

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Floating of Ice on Liquid Water

• Ice floats in liquid water because hydrogen bonds in ice are more “ordered,” making ice less dense

• Water reaches its greatest density at 4°C

• If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

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Ice and Insulation

31

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Solute Solvent Solution

Aqueous solution

Hydration shell

33

“Like Dissolves Like”

34

35

Polar Polar

Hydrophilic

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Polar Nonpolar

Hydrophobic

Colloid

37

Solute Concentration in Aqueous Solutions

• Most biochemical reactions occur in water

• Chemical reactions depend on collisions of molecules and therefore on the concentration of solutes in an aqueous solution

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• Molecular mass: the sum of all masses of all atoms in a molecule

• Numbers of molecules are usually measured in moles, where 1 mole (mol) = 6.02 x 1023 molecules

• Avogadro’s number and the unit dalton were defined such that 6.02 x 1023 daltons = 1 g

• Molarity (M): the number of moles of solute per liter of solution

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One Mole =

molecules

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Hydronium ion (H3O+)

Hydroxide ion (OH–)

2H2O

H

H

H

H

H

H

H

H

O O O O

Hydrogen is Shifty

gains H+ loses H, but keeps e-

43

Dynamic equilibrium: dissociation rate = reformation rate

44 anions cations both

45

pH Scale

Acidic [H+] > [OH–]

Neutral [H+] = [OH–]

Basic [H+] < [OH–]

7

0

14

46

pH Scale

Battery acid

Gastric juice, lemon juice

Vinegar, wine,

cola

Beer Tomato juice

Black coffee

Rainwater

Urine

Saliva

Pure water

Human blood, tears

Seawater

Inside of small intestine

Milk of magnesia

Household ammonia

Household

bleach

Oven cleaner

Basic solution

Neutral solution

Acidic solution

0

1

2

3

4

5

6

7

8

9

10

Neutral

[H+] = [OH]

Inc

rea

sin

gly

Ba

sic

[H+]

< [

OH]

Inc

rea

sin

gly

Ac

idic

[H+]

> [

OH]

H+ H+

H+

H+ H+

H+

H+

H+

OH

OH

H+

OH

H+

OH OH

OH OH H+

H+ H+

H+

OH OH

OH

OH OH OH

OH H+

11

12

13

14

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48

pH Values

49

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+

50

51

Carbonic Acid

H2CO3

Bicarbonate ion

HCO3-

Carbonic acid-Bicarbonate buffer system

H+

OH+

52

Buffering Systems

How can your commute

affect coral reef growth

in the Caribbean

Sea?

53

Acidification: A Threat to Water Quality

• Human activities such as burning fossil fuels threaten water quality

• CO2 is the main product of fossil fuel combustion

• About 25% of human-generated CO2 is absorbed by the oceans

• CO2 dissolved in sea water forms carbonic acid; this process is called ocean acidification

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• As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate

• Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals

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CO2

CO2 + H2O H2CO3

H+ + HCO3

H+ + CO32 HCO3

CaCO3 CO3

2 + Ca2+

H2CO3

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(a) (b) (c)

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• The burning of fossil fuels is also a major source of sulfur oxides and nitrogen oxides

• These compounds react with water in the air to form strong acids that fall in rain or snow

• Acid precipitation is rain, fog, or snow with a pH lower than 5.2

• Acid precipitation damages life in lakes and streams and changes soil chemistry on land

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More acidic

0

Acid rain

Normal rain

More basic

1

2

3

4

5

6

7

8

9

10

11

12

13

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