Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

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1. Label H and O Hydrogen bonds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2. A polar molecule is a molecule that has opposite charges on opposite ends The water molecule is a polar molecule: The oxygen “end” has 2 partial negative charges and the hydrogen “end” has 2 partial positive charges

3-4. Label + and – and H-bonds. Each water molecule can make a max. of 4 H-bonds with other waters. Hydrogen bonds

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 5. Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion Cohesion helps the transport of water against gravity in plants Adhesion of water to plant cell walls also helps to counter gravity

Water-conducting cells 100 µm

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Surface tension is a measure of how hard it is to break the surface of a liquid Surface tension is related to cohesion 6.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 7.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 8. A calorie is the amount of heat it takes to raise 1 gram of water 1 degree C. Kinetic energy is the energy of motion Heat is a measure of the total amount of kinetic energy due to molecular motion Temperature measures the intensity of heat due to the average kinetic energy of molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water’s High Specific Heat The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 gram of that substance to change its temperature by 1ºC Water has a high specific heat because it takes a lot of heat to get all of water’s hydrogen bonds to break Therefore, water does not change temperature easily. In other words, it takes a lot of heat to get water to change temperature Alcohol doesn’t form as many H-bonds as water, so it has a lower specific heat.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 11. Moderation of Temperature Water absorbs heat from warmer air and releases stored heat to cooler air Water can absorb or release a large amount of heat with only a slight change in its own temperature Water’s high specific heat minimizes temperature fluctuations to within limits that permit life – Heat is absorbed when hydrogen bonds break – Heat is released when hydrogen bonds form

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 12. Evaporative Cooling Evaporation is transformation of a substance from liquid to gas Heat of vaporization is the heat a liquid must absorb for 1 gram to be converted to gas As a liquid evaporates, its remaining surface cools, a process called evaporative cooling Evaporative cooling of water helps stabilize temperatures in organisms and bodies of water Examples?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Insulation of Bodies of Water by Floating Ice If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth Ice floats in liquid water because hydrogen bonds in ice form an ordered lattice making ice less dense --At 4 degrees C, water molecules get very close to each other (very dense) --At 0 degrees C, water molecules have 2 spread out in order to form the maximum of H-bonds with other water molecules.

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The Solvent of Life A solvent is the dissolving agent of a solution A solution is a liquid that is a homogeneous mixture of substances The solute is the substance that is dissolved Coffee with sugar? Water is a versatile solvent due to its polarity An aqueous solution is one in which water is the solvent

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Water is a versatile solvent due to its polarity. It is an effective solvent because it readily forms hydrogen bonds When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules, a hydration shell 17.

Na + Cl – – – – – – – – – – – –

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 17.

Lysozyme molecule in a nonaqueous environment.

17. Lysozyme molecule in a aqueous environment.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Lipids (oils, fats, and waxes) are hydrophobic and nonpolar so they can’t form hydrogen bonds with water and will not dissolve in water.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Let’s do some math…

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 22. Molarity is the number of moles of solute per liter of solution It’s gives you the concentration of the solution i.e. An 18-molar (18 M) solution is more concentrated than a 1-molar (1 M) solution

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 23. The Dissociation of Water 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 + ) – The molecule that lost the proton is now a hydroxide ion (OH - )

23. Hydronium ion (H 3 O + ) Hydroxide ion (OH – )

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The process can be described in a simplified way as the separation of a water molecule into a hydrogen ion (H + ) and a hydroxide ion (OH - ) Though statistically rare, the dissociation of water molecules has a great effect on organisms Changes in concentrations of H + and OH - can drastically affect the chemistry of a cell 23.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Effects of changes in pH Concentrations of H + and OH - are equal in pure water They are both M. The negative log of = 7, so we say that water has a pH of 7! [H+] [OH-] =

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 26. Acids and Bases 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 An acid is any substance that increases the H + concentration of a solution A base is any substance that reduces the H + concentration of a solution

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The pH Scale The pH of a solution is determined by the relative concentration of hydrogen ions Acidic solutions have pH values less than 7 Basic solutions have pH values greater than 7 Most biological fluids have pH values in the range of 6 to 8

28. pH Scale 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 – ]

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 29. 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 +

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 30. The Carbonic Acid Buffer System H 2 CO 3 ====== HCO H + Carbonic acid (H+ donor/acid), Bicarbonate (H+ acceptor/base), Hydrogen ion If the pH of the blood rises, the reaction goes to the right, releasing H+ ions If the pH of the blood drops, the reaction goes to the left, removing H+ ions

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 31. 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

More basic Normal rain More acidic Acid rain

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 32. CO 2 Emissions Combine with water in the atmosphere to form carbonic acid, which contributes to acid precipitation Contribute to global warming…and that’s a big topic. Take APES! --for now…know that changes in temperature affect food chains in both marine and land ecosystems