Chapter 3 Water and the Fitness of the Environment

Overview: 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 3-1

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 Animation: Water Structure Animation: Water Structure Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 3-2 Hydrogen bond  – – H  + + H O — —  + +  + +  + +  – –  – –  – –

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 are: – Cohesive behavior – Ability to moderate temperature – Expansion upon freezing – Versatility as a solvent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion Cohesion helps the transport of water against gravity in plants Adhesion is an attraction between different substances, for example, between water and plant cell walls

Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is related to cohesion Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Boiling Point: 100 o C Freezing Point: 0 o C Density: 1g/cm 3 Properties of Water gasliquid solid

The formation of ice As water cools to 4°C: – Molecules slow – Water contracts – Density increases Below 4°C: – Hydrogen bonds form – Water expands As water freezes: – Expands by 9%

IceDensity vs Temp ( o C)

Fig. 3-6 Hydrogen bond Liquid water Hydrogen bonds break and re-form Ice Hydrogen bonds are stable

Crocodile icefish Suborder Notothenioidei: Characteristics: Restricted to Southern Ocean No swim bladder Stenothermal Little hemoglobin and no myoglobin Larger heart and blood vessels Antifreeze proteins Mature slowly, reproduce late Antarctic Icefish

Properties of Water 1.High heat capacity 2.High heat of vaporization 3.High Surface tension 4.Polarity solvent properties

Hawaii Average Temperature Ocean Temp. ºF Land Temp. ºF

Fig. 3-4

Fig. 3-7 Cl – Na Cl – – – – – – – – – Na + – – – + Table salt dissolving in water

Water can also dissolve compounds made of nonionic polar molecules Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

H2OH2O

Formation of Peptide Bonds Peptide bond AA2

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 Oil molecules are hydrophobic because they have relatively nonpolar bonds A colloid is a stable suspension of fine particles in a liquid Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Hydrophilic head Hydrophobic tails phosphorous carbon hydrogen oxygen

Nonpolar hydrophobic tails (fatty acids) exposed to oil Polar hydrophilic heads exposed to water

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Molecular mass is 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 molecules Avogadro’s number and the unit dalton were defined such that 6.02 x daltons = 1 g Molarity (M) is the number of moles of solute per liter of solution Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 3.3: Acidic and basic conditions affect living organisms A hydrogen atom in a hydrogen bond between two water molecules can shift from one to the other: – The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H + ) – The molecule with the extra proton is now a hydronium ion (H 3 O + ), though it is often represented as H + – The molecule that lost the proton is now a hydroxide ion (OH – ) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Acids HCL  H + + Cl - Proton donor, i.e., they donate H + ions HCl is a strong acid with a pH 1-2

Bases Na + + OH -  NaOH NH 3 + H +  NH 4 OH - + H +  H 2 O HCO 3 +H +  H 2 CO 3 Proton acceptor, i.e., they take up H+ ions NaOH is a strong base ~pH 12

HCl + NaOH  H 2 O + NaCl Neutralization

Buffer- resists dramatic changes in pH; ex. tums, rolaids…buffers stomach acid

pH Scale Neutral7 Acidic0-6 Basic (alkaline)8-14 Type of Solution pH Value 0-14

pH Scale Logarithmic scale

Causes of Acid Rain Air pollution Burning of fossil fuels - Power plants - Cars, trucks, airplanes The main chemicals Sulfur dioxide Nitrogen oxides

Acid Rain Normal Rain H 2 O + CO 2  H + + HCO 3 - A pH of 5.6 Water + carbon dioxide  proton + bicarbonate Acid Rain Form of water pollution More acidic than normal rain Has pH < 5.6 nitrous dioxide + water  nitrous acid + nitric acid 2NO 2 + H 2 O  HNO 2 + HNO 3 sulfur dioxide + water  sulfuric acid SO 2 + H 2 O  H 2 SO 4

Ecological Effects from Acid Rain in Lake System Changes begin to occur as soon as a lake starts to lose it natural bases or alkalinity. 1.A large reduction in the number of plankton & invertebrates. 2.The rate of decomposition of organic matter decreases 3.Direct effects on fishes reproductive cycles. 4.A calcium deficiency in fish leads to bone malformation. 5.Fish can suffocate as their gills become clogged with aluminum hydroxide. 6.Songbirds are effected by eating insects contaminated with toxic metals.

Acid Rain on Forests

VOG on Crops Table 2. Soil pH range for optimum growth of some crops. Crop pH Alfalfa Avocado Azalea Ginger Macadamia Pineapple Sugarcane Taro Protea flower crop Big Island

Effects from Acid Rain

Acid Rain

Ocean Acidity

Global Ocean Acidity

Consequences of Ocean Acidity Animals with CaCO 3 skeletons affected Plankton Corals Mollusks Fish o.uk/2/hi/science /nature/ stm Fisheries

Acid Rain in Marine Environment reduces ability of marine organisms to utilize calcium carbonate Coral calcification rate reduced 15-20% Skeletal density decreased, branches thinner