CHAPTER 3WATER AND THE FITNESS OF THE

ENVIRONMENT

1. The polarity of water molecules results in hydrogen bonding

2. Organisms depend on the cohesion of water molecules

3. Water moderates temperatures on Earth

4. Oceans and lakes don’t freeze solid because ice floats

5. Water is the solvent of life

6. Organisms are sensitive to changes in pH

7. Acid precipitation threatens the fitness of the environment

Overview

1. The polarity of water molecules results from hydrogen bonding• Water molecule- two

hydrogen atoms form _________________ bonds with an oxygen atom.

• Partial negative charge

• Partial positive charge

________- because each share one electron_______- because O is more electronegative than H________- because they each share electrons

• Water has unusual properties because of attractions between ________ molecules.

• The slightly negative regions interact with slightly positive regions of nearby molecules, forming a __________________.

• Each water molecule can form hydrogen bonds with up to _______ neighbors.

Fig. 3.1

• Hydrogen bonds in water molecules 1/20th as strong as covalent bonds.

• They form, break, and reform with great frequency.

• A substantial percentage of all water molecules are bonded to their neighbors, creating a high level of structure.

• Hydrogen bonds hold the substance together, a phenomenon called __________

2. Organisms depend on the cohesion of water molecules

• Water cohesion is key role in the _____________ in plants.

• Water that evaporates from a leaf is replaced by water from vessels in the leaf.

• Hydrogen bonds cause water molecules leaving the veins to tug on molecules further down.

• This upward pull is transmitted to the roots.

• ___________, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels.

Fig. 3.2

• ________________, a measure of the force necessary to stretch or break the surface of a liquid, is related to cohesion.

• Water has a greater _______________ than most other liquids because hydrogen bonds among surface water molecules _________________ or breaking the surface.

• Water behaves as if covered by an invisible film.

Fig. 3.3

• Water _______________ air temperatures by ________________ heat from warmer air and releasing heat to cooler air.

• Water can absorb or release relatively __________________ of heat with only a slight change in its own temperature.

3. Water moderates temperatures onEarth

• Atoms and molecules have __________________, the energy of motion, because they are always moving.

• As speed increases, kinetic energy increases

• _____ = total ___________ of kinetic energy (due to molecular motion in a body of matter).

• __________________ = intensity of heat due to the __________ kinetic energy of molecules.

• As the average speed of molecules increases, a thermometer will record an increase in temperature.

• Heat and temperature are related, but not identical.

In most biological settings, temperature is measured on the __________________

• At sea level, water freezes at ____ and boils at ______.

• Human body temperature averages 37 oC.

• How do we measure heat?

• In ______________

• One ____________ is the amount of heat energy necessary to raise the temperature of one g of water by 1oC.

• Or ________ J), 1 J = 0.239 cal.

• _________________ = amount of heat that must be absorbed or lost for 1g of that substance to change its temperature by 1oC.

• By definition, the specific heat of water is ______________________ or 1 cal/g/oC.

• Water has a high specific heat

• Ethyl alcohol has a specific heat of 0.6 cal/g/oC.

• Iron is 0.1 cal/g/oC.

• Water resists changes in temperature

• Why? Because it absorbs or releases a relatively large quantity of heat for each degree of change.

• Why does water have a high specific heat? __________________________

• Heat must be absorbed to break ____________________ and is released when hydrogen bonds form.

• Water’s high ___________________ affects the entire whole Earth environment and individual organisms.

• A large body of water can absorb a large amount of heat from the sun in daytime and during the summer, while warming only a few degrees.

• Coastal land areas have more stable temperatures than inland areas.

• Water ________________ the composition of biological organisms better than if composed of a liquid with a lower ________________.

• The transformation of a molecule from a liquid to a gas is called _______________ or _____________.

• This occurs when the molecule moves fast enough that it can overcome the ______________ of other molecules in the liquid.

• Heating a liquid increases the _____________________ and increases the rate of ________________.

• As a liquid evaporates, the surface of the liquid that remains behind cools - __________________.

• The most energetic molecules evaporate, leaving the lower kinetic energy molecules behind.

• Evaporative cooling moderates _______________ in lakes and ponds and prevents terrestrial organisms from overheating.

• Evaporation of water from the leaves of plants or the skin of humans removes excess heat.

• Water (unlike most liquids) is less dense as a solid than as a liquid.

• At temperatures above 4oC, water behaves like other liquids, expanding when it warms and contracting when it cools.

• ____________________

• Answer: Water begins to ______ when its molecules are no longer moving vigorously enough to break their ___________________.

4. Oceans and lakes don’t freeze solid because ice floats

• At 0oC-water becomes a ___________________ with each molecule bonded to the maximum of______ partners.

• At 40C- some hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state.

• Ice is about ________ dense than water at 4oC, thus ice ______.

Fig. 3.5

If ice sank, eventually all ponds, lakes, and even the ocean would freeze solid.

• A liquid that is a completely homogeneous mixture of two or more substances is called a _________- A completely _____________ mixture of substances.

• __________= dissolving agent

• _________ = agent being dissolved.

• Example-water is a solvent and sugar the solute.

5. Water is the solvent of life

• Water is an effective __________ because it so readily forms hydrogen bonds with __________and _______ covalent molecules.

• In salt (NaCl) the Na+ cations form hydrogen bonds with partial negative oxygen regions of water molecules.

• The Cl- anions form hydrogen bonds with the partial positive hydrogen regions

Fig. 3.7

Na+ and CL- ions are dissociated

Big point- Polar molecules are also soluble in water

• Any substance that has an affinity for water is _____________________.

• These substances are dominated by _____________ bonds.

• Substances that have no affinity for water are ___________________.

• These substances are dominated by ______________________ covalent bonds.

• Example-Oils, such as vegetable oil, are non-polar

• Hydrophobic molecules are major ingredients of ______________________________

Hydrophobic vs. hydrophilic

• # of molecules in a mole = ____________________ =6.02 x 1023.

• 1 mole ethyl alcohol (C2H6O) = 46g (also contains _______________________

How do measure amounts? Answer- In ______• A ____________ = molecular weight (in grams)

• Example - sucrose (C12H22O11)

• A carbon atom weighs 12 daltons, hydrogen 1 dalton, and oxygen 16 daltons.

• The _________________ of sucrose is 342 D.

• (12 x 12D) + (22 x 1D) + (11 x 16D)

• Thus, one mole of sucrose weighs 342 g

• The concentration of a material in solution is called its ____________.

• A ___________________ has one mole of a substance dissolved in one liter of solvent, typically water.

• Example: To make a 1 molar (1 M) solution of sucrose we would add water to ______ of sucrose until the total volume was 1 liter.

• How do we measure acidity?

• Answer: __________________

• A water molecule dissociates into a hydrogen ion and a hydroxide ion:

• H2O <=> H+ + OH-

• At equilibrium the concentration of H+ or OH- is 10-7M (25°C) .

• Hydrogen and hydroxide ions are very reactive, and thus drastically affect the proteins and other molecules of a cell.

• An _______ increases the hydrogen ion concentration in a solution.

• When hydrochloric acid is added to water, hydrogen ions _______________ from chloride ions:

• HCl -> H+ + Cl-

• Addition of an acid makes a solution more _______.

6. Organisms are sensitive to changes inpH

• Any substance that reduces the hydrogen ion concentration in a solution is a ______.

•________________________

• _______ acids or bases (e.g. HCl and NaOH) dissociate completely in water

• ______ acids or bases don’t fully dissociate.

• Example: _____________ (H2CO3) is a weak acid:

• H2CO3 <=> HCO3- + H+

• At equilibrium, 1% of the molecules will be dissociated.

• The ____________ of their ___ and ___ concentrations is constant at _____.

• [H+] [OH-] = 10-14

• In a neutral solution, [H+] = ____ and [OH-] = _____

• If add acid, H+ ions increase and OH- ions decrease.

• The H+ and OH- concentrations of solutions can vary by a factor of 100 trillion or more.

• The H+ and OH- concentrations are typically expressed via the _________.

• The pH scale, ranging from __________, compresses the range of concentrations by employing __________

• ___________________________

• In a neutral solution [H+] = _____, and the pH = ___.

• Values for pH decline as [H+] _________.

• Most biological fluids have pH values in the range of _______.

• Each pH unit represents a __________ difference in H+ and OH- concentrations.

Fig. 3.9

• ________________ (a product of the formation of carbonic acid from carbon dioxide and water) occurs when rain, snow, or fog has a pH that is more acidic than 5.6.

7. Acid precipitation threatens the fitness of the environment

• Acid precipitation is caused primarily by ___________________ and ___________________ from burning of fossil fuels

• Rain in the Adirondack Mountains of upstate New York averages a ___________

• Great impact on eggs and early developmental stages of _____________________

• This has done major damage to forests in Europe and substantial damage of forests in North America