Water and the Fitness of the EnvironmentChapter 3

Drops on plasticPaper clip

Molecule That Supports All of Life

•Cells are ~70–95% water

•Water is the main reason the Earth is habitable

•Water is versatile!

75% of the Earths surface is water

water molecules and hydrogen bonding

•Water is a polar molecule:▫opposite ends have

opposite charges

•Note hydrogen bonds

Four emergent properties of water1. Cohesion

water molecules “stick” together

transports water against gravity in all vascular plants

Adhesion – water H-bonds to other substance

Water molecules stick together

Adhesion

Water-conductingcells

Adhesion

Cohesion

150 µm

Directionof watermovement

The video

•Surface tension = Cohesion at water/air surface

BASILISK

Detergent breaks surface tension

2. Water resists temperature change

absorbs heat from warm air, releases to cool air

Water can absorb more heat than air!

San Diego 72°

40 miles

Pacific Ocean

70s (°F)

80s

90s

100s

Santa Barbara 73°

Los Angeles (Airport) 75°

Burbank90°

Santa Ana 84° Palm Springs

106°

Absorption of heat by ocean cools the coast. At night, ocean releases heat to warm coast.

• Water has a high specific heat = amount of heat needed to change T of 1 g of a substance by 1ºC

Water is liquid over a broad range of temperatures

•What happens when a copper pot is used to heat water?

•High specific heat = need to add more energy to water to raise its temperature!

Substancec in cal/gm K orBtu/lb F

Aluminum 0.215

Copper 0.0923

Brass 0.092

Gold 0.030

Lead 0.0305

Silver 0.0558

Zinc 0.0925

Mercury 0.033

Alcohol(ethyl) 0.58

Water 1.00

Granite 0.19

Glass 0.20

What IS heat? Heat is energy

•Heat =average amount of kinetic energy due to molecular motion•Heat flows from more energetic area to less

(coastline example)

Faster moving molecule = hotter

•Temperature • measurement of intensity of heat

Celsius degrees (°C) Room T = Body T = Boiling =

•Evaporation = transformation from liquid to gas

•Evaporative cooling ▫Surface is cooled as water evaporates

▫Sweating and evaporative cooling

The most energetic molecules arereleased as steam. The ones left arecooler because they have lost energy

3. Ice floats

• Ice is less dense than liquid water▫Water greatest density at 4°C

• If ice sank, all water would eventually freeze solid, making life impossible

• Floating ice insulates, keeps water underneath liquid

Hydrogenbond

Liquid waterHydrogen bonds break and re-form

IceHydrogen bonds are stable

The “locked” hydrogen bonds in ice space the molecules further apart, resulting in fewer molecules per equal volume of water

hydrogen bonds in ice are more ordered in ice

Most ectotherms cannot tolerate freezing: north american wood frog

4. Water is a great medium for dissolving substances like nutrients/wastes•Solution=liquid that is a homogeneous

mixture of substances

▫ solvent =dissolving agent If water, the solution is aqueous

▫solute =substance that is dissolved Ex. salt

•hydrophilic substance has affinity for water

•hydrophobic does not

•colloid =stable suspension of fine particles in a liquid

• Cant see in microscope, nevers settle out!

pH and solutions

•Changes in concentrations of H+ and OH– can drastically affect cell

•pH =measure of the [H+] of a solution

•The pH scale is logarithmic

pH = –log [H+]

Effects of Changes in pH

• Acid = higher [H+] = lower pH▫ Acidic solutions pH < 7

• Base = higher [OH–] Alkaline/basic solutions pH >

7

•pH scale 0 – 14

▫Most biological fluids pH ?

Acids and Bases

HCl H+ + Cl - Acid or base?NaOH Na+ + OH - Acid or base?

Buffer

•Buffer =substance that resists changes in pH

Baking sodaNaHCO3 - Na+ + HCO3-

Bicarb ions can act either as an acid (donate H+) or as a base (accept H+ to form H2CO3).