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 cells are about 70-95% water water is the main reason the Earth is habitable

Water is the biological medium on Earth

All living organisms require water

cells are about 70-95% water

water is the main reason the Earth is habitable

Structure of Water Water is a polar Polarity allows water molecules to form hydrogen bonds with each other Animation: Water Structure

Water is a polar

Polarity allows water molecules to form hydrogen bonds with each other

Four emergent properties of water Water’s properties that contribute to an environment for life: Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent

Water’s properties that contribute to an environment for life:

Cohesive behavior

Ability to moderate temperature

Expansion upon freezing

Versatility as a solvent

Cohesion Cohesion = attraction of water molecules for each other due to H-bonding Ex: transport of water against gravity in plants Adhesion & Surface tension are related Animation: Cohesion of Water

Cohesion = attraction of water molecules for each other due to H-bonding

Ex: transport of water against gravity in plants

Adhesion & Surface tension are related

Moderation of Temperature Water has a high specific heat can absorb/release a large amount of heat to/from the air with only a slight change in its own temperature Temperature = a measure of the average kinetic energy of molecules Water also has a high heat of vaporization Allows for evaporative cooling Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

Water has a high specific heat

can absorb/release a large amount of heat to/from the air with only a slight change in its own temperature

Temperature = a measure of the average kinetic energy of molecules

Water also has a high heat of vaporization

Allows for evaporative cooling

Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water

Insulation of Bodies of Water by Floating Ice Ice floats (less dense) Makes aquatic life possible in winter!

Ice floats (less dense)

Makes aquatic life possible in winter!

The Solvent of Life “ Likes Dissolve Likes” Aqueous solution: solvent (water) dissolves solute Water is a versatile solvent due to its polarity

“ Likes Dissolve Likes”

Aqueous solution: solvent (water) dissolves solute

Water is a versatile solvent due to its polarity

LE 3-6 Na + Na + Cl – Cl – + + + + + + + + – – – – – – – – – – – When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell

LE 3-7b Lysozyme molecule in a aqueous environment. 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

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

A hydrophilic substance is one that has an affinity for water

A hydrophobic substance is one that does not have an affinity for water

Solute Concentration in Aqueous Solutions Chemical reactions depend on collisions of molecules Molarity (M) = moles solute per L solution 1 mole = 6.02 x 10 23 molecules 0.1 M 1.0 M

Chemical reactions depend on collisions of molecules

Molarity (M) = moles solute per L solution

1 mole = 6.02 x 10 23 molecules

Dissociation of water Water reacts with itself - transfers a proton, or hydrogen ion (H + ) The molecule with the extra proton is now a hydronium ion (H 3 O + ~ has an extra H + ) The molecule that lost the proton is now a hydroxide ion (OH - ) H 2 O + H 2 O  H 3 O + + OH - Animation: Dissociation

Water reacts with itself - transfers a proton, or hydrogen ion (H + )

The molecule with the extra proton is now a hydronium ion (H 3 O + ~ has an extra H + )

The molecule that lost the proton is now a hydroxide ion (OH - )

Effects of changes in pH Concentrations of H + and OH - are equal in pure water Adding certain solutes, called acids and bases, modifies the concentrations of H + and OH - Biologists use something called the pH scale to describe how acidic or basic (the opposite of acidic) a solution is

Concentrations of H + and OH - are equal in pure water

Adding certain solutes, called acids and bases, modifies the concentrations of H + and OH -

Biologists use something called the pH scale to describe how acidic or basic (the opposite of acidic) a solution is

Acids and Bases & pH Acid = increases the H + concentration of a solution Base = reduces the H + concentration of a solution pH of a solution is determined by the relative concentration of H + ions Acidic pH < 7 Basic pH > 7 Most biological fluids have pH values in the range of 6 to 8 Animation: Acids, Bases & pH

Acid = increases the H + concentration of a solution

Base = reduces the H + concentration of a solution

pH of a solution is determined by the relative concentration of H + ions

Acidic pH < 7

Basic pH > 7

Most biological fluids have pH values in the range of 6 to 8

LE 3-8 pH Scale 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Oven cleaner Household bleach Household ammonia Milk of magnesia Seawater Pure water Human blood Urine Rainwater Black coffee Tomato juice Vinegar, beer, wine, cola Digestive (stomach) juice, lemon juice Battery acid Neutral [H + ] = [OH – ] Increasingly Acidic [H + ] > [OH – ] Increasingly Basic [H + ] < [OH – ]

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 +

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 +

The Threat of Acid Precipitation Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6 Acid precipitation is caused mainly by the mixing of different pollutants with water in the air Acid precipitation can damage life in lakes and streams Effects of acid precipitation on soil chemistry are contributing to the decline of some forests Investigation: Acid Rain

Acid precipitation refers to rain, snow, or fog with a pH lower than 5.6

Acid precipitation is caused mainly by the mixing of different pollutants with water in the air

Acid precipitation can damage life in lakes and streams

Effects of acid precipitation on soil chemistry are contributing to the decline of some forests

LE 3-9 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 More basic Normal rain More acidic Acid rain