Properties of Water and the Fitness of the Environment

Water Facts Three-quarters of the Earth’s surface is submerged in water The abundance of water is the main reason the Earth is habitable Figure 3.1

Importance of water Overview: The Molecule That Supports All of Life Water is the biological medium here on Earth All living organisms require water more than any other substance

Water Facts 1. water is a polar molecule 2. Polar – when the charge of a molecule is neutral, but uneven One side is negative, the other is positive O- H+ H+

Water Facts The polarity of water molecules results in hydrogen bonding 3. H bonds – when the negative side of H2O bonds to positive side of another H2O

Water Facts Hydrogen bonds + H  – Figure 3.2 + - O- + O- H+

Hydrogen Bonds Why would water’s ability to bond to itself be important for living organisms? (Think of plants especially)

Hydrogen Bonds Capillary action – in plants, hydrogen bonds allow water to move up a stem against gravity

Properties of water 7 emergent properties of water contribute to Earth’s fitness for life Cohesion Adhesion Surface tension Temperature Moderation High specific heat Evaporative cooling Universal solvent

Cohesion Cohesion - the bonding of water molecules to other water molecules due to hydrogen bonding

Adhesion 2. Adhesion - the bonding of water molecules to non-water molecules

Surface Tension 3. Surface tension - hydrogen bond “barrier” made on the surface of water Why does it happen? Figure 3.4

Moderation of Temperature 4. Water moderates air temperature a. absorbs heat from warm air and releases stored heat to cool air

Water’s High Specific Heat 5. specific heat capacity - the amount of heat that can be absorbed by a substance without raising its temperature

Specific Heat a. Water has a high specific heat allows it to minimize temperature fluctuations to within limits that permit life Heat is absorbed when hydrogen bonds break Heat is released when hydrogen bonds form

Specific Heat

Evaporative Cooling 6. Evaporative cooling - When water evaporates, it cools the surface it was on ex) Sweating cools the body

Insulation of Bodies of Water by Floating Ice Solid water, or ice Is less dense than liquid water Floats in liquid water Insulates water & organisms below ice layer

Insulation of Bodies of Water by Floating Ice Since ice floats in water Life can exist under the frozen surfaces of lakes and polar seas

The Solvent of Life 7. Because it is polar, water is a versatile solvent Other polar things dissolve in water Called the universal solvent because so many substances dissolve in water

Water can also interact with polar molecules such as proteins This oxygen is attracted to a slight positive charge on the lysozyme molecule. This oxygen is attracted to a slight negative charge on the lysozyme molecule. (a) Lysozyme molecule in a nonaqueous environment (b) Lysozyme molecule (purple) in an aqueous environment such as tears or saliva (c) Ionic and polar regions on the protein’s Surface attract water molecules. + – Figure 3.7

Hydrophilic and Hydrophobic Substances hydrophobic substance - no affinity for water Ex) Nonpolar substances and lipids

Hydrophilic and Hydrophobic Substances 2. hydrophilic substance has affinity for water Ex) Polar or ionic, like carbohydrates and salts

Solute Concentration in Aqueous Solutions Since most biochemical reactions occur in water inside cells (aqueous environments) It is important to learn to calculate the concentration of solutes in an aqueous solution

Moles and Molarity A mole Represents an exact number of molecules of a substance in a given mass Molarity Is the number of moles of solute per liter of solution

Acids and Bases Dissociation of water molecules leads to acidic and basic conditions that affect living organisms Organisms must maintain homeostasis in the pH of their internal and external environments

Effects of Changes in pH Water can dissociate Into hydronium ions (H+ or H3O+) and hydroxide (OH-) ions Changes in the concentration of these ions Can have a great affect on pH in living organisms H Hydronium ion (H3O+) Hydroxide ion (OH–) + – Figure on p. 53 of water dissociating

Acids and Bases An acid Is any substance that increases the hydrogen ion concentration of a solution A base Is any substance that reduces the hydrogen ion concentration of a solution (more OH- ions)

The pH Scale Scale goes from 0-14 with 7 neutral The pH of a solution Is determined by the relative concentration of hydrogen ions Difference of 10X in hydrogen ion concentration between any two pH values Acids have a higher number of H+ ions than a base Acids produce H+ ion in solution Bases produce OH- ions in solution

The pH scale and pH values of various aqueous solutions Increasingly Acidic [H+] > [OH–] Increasingly Basic [H+] < [OH–] Neutral [H+] = [OH–] Oven cleaner 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH Scale Battery acid Digestive (stomach) juice, lemon juice Vinegar, beer, wine, cola Tomato juice Black coffee Rainwater Urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach Figure 3.8

Buffers The internal pH of most living cells Buffers Must remain close to pH 7 Buffers Are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution Consist of an acid-base pair that reversibly combines with hydrogen ions Made by organisms

The Threat of Acid Precipitation Refers to rain, snow, or fog with a pH lower than pH 5.6 Is caused primarily by the mixing of different pollutants with water in the air

Can damage life in Earth’s ecosystems Acid precipitation Can damage life in Earth’s ecosystems 1 2 3 4 5 6 7 8 9 10 11 12 13 14 More acidic Acid rain Normal rain More basic Figure 3.9