Slide 1 / 44 Slide 2 / 44 Chapter 3 Water: Supports All Life Water is the biological medium on Earth Water and the Fitness of All living organisms the Environment require water more than any other substance Most cells are surrounded by water, and cells consist of about 70-95% water Slide 3 / 44 Slide 4 / 44 Water and Earth Hydrogen Bonding of water The polarity of water molecules results in hydrogen bonding - Three-quarters of the Earth’s The water molecule is a polar molecule due to uneven distribution of electrons. surface is submerged in water The opposite ends of a water molecule have opposite charges. + + The abundance of water is the main reason the Earth is habitable Slide 5 / 44 Slide 6 / 44 1 In a single molecule of water, the two hydrogen Polarity atoms are bonded to a single oxygen atom by The polarity of water molecules allows them to form hydrogen A hydrogen bonds. bonds with each other and contributes to the various properties water exhibits B nonpolar covalent bonds. C polar covalent bonds. D ionic bonds. E van der Waals interactions. click here for an animation about water
Slide 7 / 44 Slide 8 / 44 2 The slight negative charge at one end of one Four properties of water water molecule is attracted to the slight positive charge of another water molecule. What is this attraction called? All contribute to Earth’s fitness for life A a covalent bond B a hydrogen bond Cohesive behavior Ability to moderate temperature C an ionic bond Expansion upon freezing D a hydrophilic bond Versatility as a solvent E a hydrophobic bond Slide 9 / 44 Slide 10 / 44 Cohesion Cohesion and Adhesion Cohesion helps pull water Water molecules exhibit cohesion up through the Water conducting cells microscopic vessels of Cohesion is the bonding of a high plants percentage of the molecules to neighboring molecules Adhesion of water to plant cell walls also helps Cohesion is due to hydrogen counteract the force of bonding gravity 100 µ m 100 m m click here for a video on cohesion and adhesion Slide 11 / 44 Slide 12 / 44 3 What determines the cohesiveness of water Surface Tension molecules? A hydrophobic interactions B nonpolar covalent bonds C ionic bonds Surface tension is related to D cohesion hydrogen bonds E both A and C It is a measurement of how hard it is to break the surface of a liquid
Slide 13 / 44 Slide 14 / 44 4 Which of the following is possible due to the 5 What do cohesion, surface tension, and high surface tension of water? adhesion have in common with reference to water? A All increase when temperature increases. A Lakes don't freeze solid in winter, despite low temperatures. B All are produced by ionic bonding. B A water strider can walk across the surface of a small pond. C All are properties related to hydrogen bonding. C Organisms resist temperature changes, although they give off D All have to do with nonpolar covalent bonds. heat due to chemical reactions. E C and D only D Water can act as a solvent. E The pH of water remains exactly neutral. Slide 15 / 44 Slide 16 / 44 Review: Heat and Temperature Moderation of Temperature Kinetic energy is the energy of motion Water moderates air temperature by absorbing Heat is a measure of the total amount of kinetic heat from warmer air and energy due to molecular motion releasing the stored heat to cooler air. Temperature measures the intensity of heat due to average KE of molecules Water can absorb or release a large amount to heat with only a slight change in its own temperature. Slide 17 / 44 Slide 18 / 44 Water’s High Specific Heat Hydrogen Bonding and Specific Heat Water has a high specific heat, which allows it to minimize temperature fluctuations to within limits that permit life The specific heat of a substance is the amount of heat that must be Heat must be absorbed in order to break absorbed or lost for 1 gram of that hydrogen bonds substance to change its temperature by 1ºC. Heat is released when hydrogen bonds form
Slide 19 / 44 Slide 20 / 44 Evaporation Evaporative Cooling Evaporative cooling is a process in which as liquid evaporates, its remaining Evaporation is the transformation of a substance surface cools from a liquid to a gas Evaporative cooling is due to Heat of vaporization is the water’s high heat of quantity of heat a liquid must vaporization absorb for 1 gram of it to be converted from a liquid to a Evaporative cooling of water gas helps stabilize temperatures in living things and in bodies of water Slide 21 / 44 Slide 22 / 44 Floating Ice 6 Water's high specific heat is mainly a consequence of the The hydrogen bonds in ice are more “ordered” than in liquid water, making ice less dense, A small size of the water molecules. and able to float. B high specific heat of oxygen and hydrogen atoms. absorption and release of heat when hydrogen bonds C break and form. D fact that water is a poor heat conductor. E inability of water to dissipate heat into dry air. Slide 23 / 44 Slide 24 / 44 The Solvent of Life Water can also interact with large polar molecules such as proteins. Ionic and polar regions on the protein’s surface attract water molecules. Lysozyme molecule in a Lysozyme molecule in an nonaqueous environment. aqueous environment such as tears or saliva.
Slide 25 / 44 Slide 26 / 44 7 Ice is lighter and floats in water because it is a Hydrophilic and Hydrophobic Substances crystalline structure in which each water molecule is bonded to a maximum of four other water molecules by which kind of bond? A hydrophobic substance A hydrophilic substance does not have an affinity for has an affinity for water A ionic water B hydrogen C covalent D A and C only E A, B, and C Slide 27 / 44 Slide 28 / 44 Solute Concentration in Aqueous Solutions Aqueous Solutions Calculations A mole represents an exact number of molecules of a Most biochemical reactions occur in substance, 6.02 x 1023 water Molarity is the number of moles of solute per liter of Therefore, it is important to learn to solution calculate the concentration of solutes in an aqueous solution Concentrations of aqueous solutions may also be measured in mass percent, e.g. 10% salt solution Slide 29 / 44 Slide 30 / 44 Dissociation of water – + H H H O O Dissociation of water molecules leads to acidic and basic H H H conditions that affect living organisms Hydronium Hydroxide ion (H 3 O + ) – ) ion (OH Water can dissociate into hydronium ions and hydroxide ions Changes in the concentration of these ions can have a great click here for an animation affect on living organisms about hydrogen bonding
Slide 31 / 44 Slide 32 / 44 Effects of Changes in pH Acids and Bases Concentrations of H + and OH - are equal in pure water H+ An acid is any substance that increases the hydrogen ion Adding certain solutes, called concentration of a solution. acids and bases, modifies the concentrations of H + and OH - A base is any substance that OH- Biologists use the pH scale to reduces the hydrogen ion describe how acidic or basic (or concentration of a solution alkaline) a solution is Slide 33 / 44 Slide 34 / 44 The pH Scale The pH Scale Increasingly [H+] > [OH–] The pH of a solution is determined by the relative concentration of hydrogen ions Acidic The pH scale and pH values The pH of acids are low, below 7 of various aqueous solutions The pH of bases are above 7 up to 14 Neutral [H+] = [OH–] Most biological fluids have pH values around 6-8 Increasingly [H+] < [OH–] Basic Slide 35 / 44 Slide 36 / 44 Buffers Acid Precipitation The internal pH of most living cells must remain close to pH 7 Acid precipitation refers to rain, snow, or fog with a pH lower than pH 5.6 Buffers are substances that minimize changes in the concentrations of hydrogen and hydroxide ions in a solution Caused primarily by the They consist of an acid-base pair mixing of different pollutants that reversibly combines with with water in the air hydrogen ions
Slide 37 / 44 Slide 38 / 44 8 A given solution contains 0.0001(10 -4 ) moles of Acid Precipitation hydrogen ions [H+] per liter. Which of the following best describes this solution? 0 More 1 acidic Acid precipitation 2 3 A acidic: H+ acceptor Acid can damage life in rain 4 B basic: H+ acceptor Earth’s water and 5 Normal rain C acidic: H+ donor soil ecosystems, 6 7 such as lakes, D basic: H+ donor streams and 8 E neutral 9 forests 10 11 More 12 basic 13 14 Slide 39 / 44 Slide 40 / 44 9 What would be the pH of a solution with a 10 What would be the pH of a solution with a hydrogen ion [H + ] concentration of 10 -8 M? hydroxide ion [OH - ] concentration of 10 -12 M? pH = - log [H + ] K w = 10 -14 A pH 2 B pH 4 A pH 2 C pH 6 B pH 4 D pH 8 C pH 10 E pH 10 D pH 12 E pH 14 Slide 41 / 44 Slide 42 / 44 11 Which of the following solutions has the 12 Which of the following statements is true about greatest concentration of hydrogen ions [H + ]? buffer solutions? They maintain a constant pH when bases are added to them but not A when acids are added to them. A gastric juice at pH 2 They maintain a constant pH when acids are added to them but not B when bases are added to them. B vinegar at pH 3 C tomato juice at pH 4 C They maintain a constant pH of exactly 7 in all living cells and biological fluids. D black coffee at pH 5 E household bleach at pH 12 D They maintain a relatively constant pH. E They are found only in living systems and biological fluids.
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