Chapter 3 Water and Life

Overview: The Molecule That Supports All of Life Water = biological medium on Earth Living things need water Most cells surrounded by water cells are about 70–95% water Earth is habitable bc of abundance of water © 2011 Pearson Education, Inc.

Figure 3.1 Figure 3.1 How does the habitat of a polar bear depend on the chemistry of water? 3

Concept 3.1: Polar covalent bonds in water molecules result in hydrogen bonding Water molecule is polar molecule: ends have opposite charges Polarity allows water molecules to form hydrogen bonds with each other https://www.brainpop.com/science/earthsystem/water/ https://youtu.be/cXefyS9p1BE https://youtu.be/PVL24HAesnc © 2011 Pearson Education, Inc.

Animation: Water Structure Right-click slide/select “Play” © 2011 Pearson Education, Inc. 5

  Hydrogen bond  + Polar covalent bonds    +    +    + Figure 3.2   Hydrogen bond  + Polar covalent bonds    +    +    + Figure 3.2 Hydrogen bonds between water molecules. 6

Figure 3.UN01 Figure 3.UN01 Concept Check 3.1, question 2 7

It is a linear molecule, as in H-O-H. Which one of the following hypothetical changes in a water molecule would tend to make it more polar? It is a linear molecule, as in H-O-H. Adjacent water molecules form covalent bonds with each other. The electronegativity values for H is increased. The electronegativity value for O is increased. All of the above would make water more polar.

Concept 3.2: Four emergent properties of water contribute to Earth’s suitability for life Four properties facilitate an environment for life: Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent © 2011 Pearson Education, Inc.

The four emergent properties of water that are important for life are: Cohesion, expansion upon freezing, high heat of evaporation, and capillarity Cohesion, moderation of temperature, expansion upon freezing, and solvent properties Moderation of temperature, solvent properties, high surface tension, and capillarity Heat of vaporization, high specific heat, high surface tension, and capillarity Polarity, hydrogen bonding, high specific heat, and high surface tension

Cohesion of Water Molecules Hydrogen bonds hold water molecules together= cohesion Cohesion helps the transport of water against gravity in plants Adhesion = attraction between different substance Ex: between water and plant cell walls © 2011 Pearson Education, Inc.

Animation: Water Transport Right-click slide/select “Play” © 2011 Pearson Education, Inc. 12

Two types of water-conducting cells Figure 3.3 Adhesion Two types of water-conducting cells Cohesion Direction of water movement Figure 3.3 Water transport in plants. 300 m 13

Two types of water-conducting cells Figure 3.3a Two types of water-conducting cells Figure 3.3 Water transport in plants. 300 m 14

Surface tension is related to cohesion Surface tension measures how hard it is to break the surface of a liquid Surface tension is related to cohesion © 2011 Pearson Education, Inc.

Figure 3.4 Figure 3.4 Walking on water. 16

Moderation of Temperature by Water Water absorbs heat from warmer air  releases stored heat to cooler air © 2011 Pearson Education, Inc.

Heat and Temperature Kinetic energy = energy of motion Heat = total amount of kinetic energy due to molecular motion Temperature = intensity of heat due to average kinetic energy of molecules © 2011 Pearson Education, Inc.

A calorie (cal) =heat required to raise f 1 g of water 1°C Celsius scale A calorie (cal) =heat required to raise f 1 g of water 1°C Food “Calories” are kilocalories (kcal) kcal = 1,000 cal Joule (J) = unit of energy 1 J = 0.239 cal, or 1 cal = 4.184 J © 2011 Pearson Education, Inc.

Water’s High Specific Heat Specific heat =amount of heat absorbed or lost for 1 g to change temperature 1ºC Water = 1 cal/g/ºC Water resists changing temperature bc of its high specific heat © 2011 Pearson Education, Inc.

Water’s high specific heat bc of hydrogen bonds Heat absorbed when H bonds break Heat released when H bonds form © 2011 Pearson Education, Inc.

High specific heat of water keeps temp changes moderatepermits life

Los Angeles (Airport) 75° Figure 3.5 San Bernardino 100° Burbank 90° Santa Barbara 73° Riverside 96° Los Angeles (Airport) 75° Santa Ana 84° Palm Springs 106° 70s (°F) 80s Pacific Ocean 68° 90s Figure 3.5 Effect of a large body of water on climate. 100s San Diego 72° 40 miles 23

Evaporative Cooling Evaporation = liquid to gas Heat of vaporization = heat a liquid must absorb for 1 g to convert to gas Evaporationremaining surface cools= evaporative cooling Evaporative cooling stabilizes temps in organisms and bodies of water © 2011 Pearson Education, Inc.

Floating of Ice on Liquid Water Ice floats in liquid water bc hydrogen bonds in ice are more “ordered”  ice less dense Water most dense at 4°C If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth © 2011 Pearson Education, Inc.

Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Figure 3.6 Hydrogen bond Liquid water: Hydrogen bonds break and re-form Figure 3.6 Ice: crystalline structure and floating barrier. Ice: Hydrogen bonds are stable 26

Figure 3.6a Figure 3.6 Ice: crystalline structure and floating barrier. 27

Water: The Solvent of Life Solution = homogeneous mixture Solvent =dissolving agent of a solution Solute =substance that is dissolved Aqueous solution =water is the solvent © 2011 Pearson Education, Inc.

hydration shell- ions surrounded by water molecules © 2011 Pearson Education, Inc.

                   Na Na Cl Cl Figure 3.7 Figure 3.7 Table salt dissolving in water. 30

Water can also dissolve nonionic polar molecules Large polar molecules (ex.protein) can dissolve in water if ionic and polar regions © 2011 Pearson Education, Inc.

Figure 3.8  +      + Figure 3.8 A water-soluble protein. 32

Hydrophilic and Hydrophobic Substances A hydrophilic substance = has affinity for water A hydrophobic substance does not have affinity for water Oil molecules = hydrophobic bc mostly nonpolar bonds A colloid =stable suspension of small particles in a liquid © 2011 Pearson Education, Inc.

Solute Concentration in Aqueous Solutions Most biochemical reactions occur in water Chemical reactions depend on collisions of molecules [conc] of solutes is important © 2011 Pearson Education, Inc.

Molecular mass =sum of mass of atoms in molecule # molecules measured in moles(1 mole (mol) = 6.02 x 1023 molecules) 6.02 x 1023 daltons = 1 g Molarity (M) = # moles of solute per liter of solution © 2011 Pearson Education, Inc.

Possible Evolution of Life on Other Planets with Water Properties of water support life on Earth: Astrobiologists search for planets with water >200 planets found outside our solar system; one or two contain water In our solar system, Mars has water © 2011 Pearson Education, Inc.

Figure 3.9 Figure 3.9 Subsurface ice and morning frost on Mars. 37

Concept 3.3: Acidic and basic conditions affect living organisms 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 (H3O+), though it is often represented as H+ The molecule that lost the proton is now a hydroxide ion (OH–) © 2011 Pearson Education, Inc.

Water is in a state of dynamic equilibrium in which water molecules dissociate at the same rate at which they are being reformed © 2011 Pearson Education, Inc.

+  Hydronium ion (H3O+) Hydroxide ion (OH) Figure 3.UN02 +  2 H2O Hydronium ion (H3O+) Hydroxide ion (OH) Figure 3.UN02 In-text figure, p. 53 40

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 © 2011 Pearson Education, Inc.

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 whether a solution is acidic or basic (the opposite of acidic) © 2011 Pearson Education, Inc.

Acids and Bases 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 © 2011 Pearson Education, Inc.

The pH Scale In any aqueous solution at 25°C the product of H+ and OH– is constant and can be written as The pH of a solution is defined by the negative logarithm of H+ concentration, written as For a neutral aqueous solution, [H+] is 10–7, so [H+][OH–] = 10–14 pH = –log [H+] pH = –(–7) = 7 © 2011 Pearson Education, Inc.

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 © 2011 Pearson Education, Inc.

pH Scale 1 2 Increasingly Acidic [H+] > [OH] 3 4 Acidic solution 5 Figure 3.10 pH Scale 1 Battery acid 2 Gastric juice, lemon juice H+ H+ H+ Vinegar, wine, cola H+ OH 3 Increasingly Acidic [H+] > [OH] OH H+ H+ H+ H+ 4 Acidic solution Tomato juice Beer Black coffee 5 Rainwater 6 Urine OH OH Neutral [H+] = [OH] Saliva OH 7 H+ H+ Pure water OH OH Human blood, tears H+ H+ H+ 8 Seawater Neutral solution Inside of small intestine 9 Figure 3.10 The pH scale and pH values of some aqueous solutions. 10 Increasingly Basic [H+] < [OH] Milk of magnesia OH OH 11 OH H+ OH OH Household ammonia OH H+ OH 12 Basic solution Household bleach 13 Oven cleaner 14 46

Figure 3.10a Figure 3.10 The pH scale and pH values of some aqueous solutions. 47

Figure 3.10b Figure 3.10 The pH scale and pH values of some aqueous solutions. 48

Figure 3.10c Figure 3.10 The pH scale and pH values of some aqueous solutions. 49

Figure 3.10d Figure 3.10 The pH scale and pH values of some aqueous solutions. 50

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+ http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/buffer12.swfhttp://www.chemistry.uoguelph.ca/educmat/chm19104/chemtoons/chemtoons7.htm © 2011 Pearson Education, Inc.

Acidification: A Threat to Water Quality Human activities such as burning fossil fuels threaten water quality CO2 is the main product of fossil fuel combustion About 25% of human-generated CO2 is absorbed by the oceans CO2 dissolved in sea water forms carbonic acid; this process is called ocean acidification © 2011 Pearson Education, Inc.

CO2 CO2 + H2O H2CO3 H2CO3 H+ + HCO3 H+ + CO32 HCO3 CO32 + Ca2+ Figure 3.11 CO2 CO2 + H2O H2CO3 H2CO3 H+ + HCO3 H+ + CO32 HCO3 Figure 3.11 Atmospheric CO2 from human activities and its fate in the ocean. CO32 + Ca2+ CaCO3 53

As seawater acidifies, H+ ions combine with carbonate ions to produce bicarbonate Carbonate is required for calcification (production of calcium carbonate) by many marine organisms, including reef-building corals © 2011 Pearson Education, Inc.

Figure 3.12 Figure 3.12 IMPACT: The Threat of Ocean Acidification to Coral Reef Ecosystems (a) (b) (c) 55

Figure 3.12a Figure 3.12 IMPACT: The Threat of Ocean Acidification to Coral Reef Ecosystems (a) 56

Figure 3.12b Figure 3.12 IMPACT: The Threat of Ocean Acidification to Coral Reef Ecosystems (b) 57

Figure 3.12c Figure 3.12 IMPACT: The Threat of Ocean Acidification to Coral Reef Ecosystems (c) 58

Acid precipitation is rain, fog, or snow with a pH lower than 5.2 The burning of fossil fuels is also a major source of sulfur oxides and nitrogen oxides These compounds react with water in the air to form strong acids that fall in rain or snow Acid precipitation is rain, fog, or snow with a pH lower than 5.2 Acid precipitation damages life in lakes and streams and changes soil chemistry on land © 2011 Pearson Education, Inc.

                Figure 3.UN03 Figure 3.UN03 Summary figure, Concept 3.1 60

Ice: stable hydrogen bonds Liquid water: transient hydrogen bonds Figure 3.UN04 Figure 3.UN04 Summary figure, Concept 3.2 Ice: stable hydrogen bonds Liquid water: transient hydrogen bonds 61

Acidic [H+] > [OH] Neutral [H+] = [OH] Basic [H+] < [OH] Figure 3.UN05 Acidic [H+] > [OH] Acids donate H+ in aqueous solutions. Neutral [H+] = [OH] 7 Bases donate OH or accept H+ in aqueous solutions Figure 3.UN05 Summary figure, Concept 3.3 Basic [H+] < [OH] 14 62

(mmol CaCO3/m2 • day) Calcification rate Figure 3.UN06 40 (mmol CaCO3/m2 • day) Calcification rate 20 Figure 3.UN06 Test Your Understanding, question 14 200 250 [CO32] (mol/kg) 63

Figure 3.UN07 Figure 3.UN07 Appendix A: answer to Figure 3.2 legend question 64

Figure 3.UN08 Figure 3.UN08 Appendix A: answer to Summary of Concept 3.1 Draw It question 65

Figure 3.UN09 Figure 3.UN09 Appendix A: answer to Test Your Understanding, question 9 66