Chapter 3 Water and the Fitness of the Environment Why is water special? Unique Properties of Water Acidic/Basic conditions
Abundance of water is the main reason the Earth is habitable Earth’s surface – 75% submerged in water
Why is water special? Molecule that supports all life Biological Medium Metabolic Reactions Required for survival of all living organisms Exists in nature in all 3 states
Water Structure Polar molecule Dipole H bonds Contributes to unique properties
What’s wrong with this picture?
Unique Properties of Water Ice floats a. Less dense than liquid water b. H bonds more ordered and stable in solid water
Since Ice floats in water Life can exist under the frozen surfaces of lakes and polar seas
Unique Properties of Water Water has high specific heat Moderates air temp 1. When air is warmer 2. When air is cooler
Review terms 1. Kinetic energy 2. Heat 3. Temperature
Review terms 4. specific heat of a substance
Unique Properties of Water Water’s high specific heat a. Resists change b. Large bodies of water can absorb heat w/o large temp change c. Heat absorbed when H bonds break Heat released when H bonds form
d. Bio sig Water keeps temp fluctuations to within limits that permit life Due to H bonding, water molecules hold tightly to each other Aids in homeostasis
Unique Properties of Water High heat of vaporization a. Vaporization (evaporation) b. Heat of vaporization
Bio sig Evaporative Cooling Due to high heat of vaporization Allows water to cool a surface ex.
Unique Properties of Water Cohesion As a liquid, water forms FRAGILE H bonds H bonds are constantly breaking and reforming Definition of cohesion
Bio sig Transport of water and dissolved nutrients against gravity
Pond Walkers Bio sig 1. Surface Tension 2. Skin of tightly H bonded water molecules, forms @air/water interface
Unique Properties of Life The Solvent of Life a. Terms 1. Solution 2. Solvent 3. Solute 4. Aqueous Solution
Water is versatile solvent Hydrophilic Hydrophobic Why? Polarity Two impt features 1. shape 2. H bonds
Water has ability to dissolve macromolecules Can form sphere of hydration ex. Fig 3-7 Lysozyme molecule
Hydration shell Polar water can interact with ionic compounds called solutes and dissolve them
Most biochem rxns occur in water To calculate concentration of solutes in aqueous solutions: 1. Mole 2. Molarity
Unique Properties of Water Water and pH a. Dissociation of water molecules affect living organisms
Acid/Base 1. Acid 2. Base
pH 1. determined by relative conc of H+ ions 2. Definition pH =
pH scale 1. acidic 2. basic
Bio sig 1. Homeostasis all living orgs have a vary narrow pH range over which they can survive. 2. Organisms maintain pH by using
Buffers a. Substances that minimize changes in the concentrations of H+ and OH- ions in a solution b. Buffer systems are reversible – depends of H+ concentration
Buffers consist of: Weak acid and its anionic salt Weak acid dissociates in aq. Solution Anionic salt is the negative ion
Buffer example - Carbonic Acid CO2 + H20
Clarification
Acid Precipitation Rain, snow, or fog with a pH lower than 5.6 Caused by pollutants mixing with water in the air