Chapter 3: WATER AND THE FITNESS OF THE ENVIRONMENT

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1 BIOLOGY I Chapter 3: WATER AND THE FITNESS OF THE ENVIRONMENT Evelyn I. Milian Instructor 2012

2 Class Collaborative Activity The class will be split into small groups of 2-4 students. Each small group should work together to answer the following question and turn in your answer to the instructor: What are the functions and the importance of water for life? Write a paragraph or a list of several sentences. You can use your previous knowledge, your textbook, and any other resources available in the classroom. Evelyn I. Milian - Instructor 2

3 Functions and Properties of Water Water is one of the most important and abundant compounds in all living systems. All livings things are 70-95% water. Water exists in the natural environment in all three physical states of matter: liquid, solid (ice), and gas (water vapor). Main Functions of Water: Solvent: Water dissolves other substances (called the solutes). Stabilizing Temperature: Water has a high heat capacity, it can absorb or release a relatively large amount of heat. Chemical reactions: Water serves as the medium, as reactant or product in chemical reactions in the body. Lubricant: Water is a major part of mucus and other lubricating fluids in the body of an organism. Evelyn I. Milian - Instructor 3

4 Properties of Water: A Polar Molecule Water is a polar molecule. The red electrons are shared unequally. Because the oxygen nucleus attracts the shared electrons more strongly, the oxygen end of a water molecule has a partial negative charge; written --, and the hydrogen ends have partial positive charges, written +. Evelyn I. Milian - Instructor 4

The polarity of water molecules results in hydrogen bonding.

5 Properties of Water: Polarity Water is a polar molecule; opposite ends of the molecule have opposite charges. Oxygen attracts the shared electrons more strongly and is partially negative. The two hydrogen atoms are partially positive. The polarity of water molecules results in hydrogen bonding. The charged regions of a polar water molecule are attracted to oppositely charged parts of neighboring water molecules. Each molecule can hydrogen-bond to multiple partners, and these associations are constantly changing. The hydrogen bonds form, break, and re-form with great frequency. Evelyn I. Milian - Instructor 5

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7 Emergent Properties of Water The emergent properties of water contribute to Earth s fitness for life and water s key functions. 1. Cohesion, adhesion, surface tension 2. Moderation of temperature by water: High heat capacity or high specific heat Evaporative cooling 3. Floating of ice on liquid water: Expansion upon freezing 4. Versatility as a solvent Water is the solvent of life. Evelyn I. Milian - Instructor 7

8 Emergent Properties of Water: Cohesion and Adhesion Cohesion is the binding together of like molecules, often by hydrogen bonds. Cohesion due to hydrogen bonds between water molecules contributes to the transport of water and dissolved nutrients against gravity in plants; it helps hold together the column of water within the cells. Adhesion, the attraction between different kinds of molecules, also plays a role. Adhesion of water to cell walls by hydrogen bonds helps resist the downward pull of gravity. In plants, evaporation from leaves pulls water upward from the roots through water-conducting cells. Because of the properties of cohesion and adhesion, the tallest trees can transport water more than 100 meters upward. Evelyn I. Milian - Instructor 8

Emergent Properties of Water: Cohesion and Surface Tension Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid.

9 Emergent Properties of Water: Cohesion and Surface Tension Related to cohesion is surface tension, a measure of how difficult it is to stretch or break the surface of a liquid. Water has a high surface tension because of the hydrogen bonding of surface molecules. This makes water behave as though coated with an invisible film. Due to water s high surface tension resulting from the collective strength of its hydrogen bonds, some animals can stand, walk, or run on water without breaking the surface. Evelyn I. Milian - Instructor 9

10 Emergent Properties of Water: Moderation of Temperature The ability of water to stabilize temperature stems from its relatively high heat capacity (or high specific heat) due to its hydrogen bonding. Heat, a form of energy, is a measure of the total amount of kinetic energy (energy of motion) in matter due to motion of its molecules. Specific heat is the amount of heat that must be absorbed or lost for 1 g (gram) of a substance to change its temperature by 1 C (Celsius). Compared to most other fluids, water absorbs more heat energy before it gets measurably hotter. What is the relevance of water s high heat capacity to life on Earth? Large bodies of water can absorb and store a large amount of heat from the sun and warm up only a few degrees. It stabilizes ocean temperatures, creating a favorable environment for marine life. By absorbing or releasing heat, oceans moderate coastal climates. The water that covers most of Earth keeps temperature fluctuations on land and in water within limits that permit life! Evelyn I. Milian - Instructor 10

11 Emergent Properties of Water: Moderation of Temperature Water has a high heat of vaporization, the quantity of heat a liquid must absorb for 1 g of it to be converted from the liquid to the gaseous state (evaporation). This property of water allows evaporative cooling; the surface becomes cooler during evaporation, owing to a loss of highly kinetic molecules to the gaseous state (the hottest molecules are the most likely to leave as gas). Evaporative cooling of water contributes to the stability of temperature in lakes and ponds and also provides a mechanism that prevents terrestrial organisms from overheating. For example, evaporation of sweat from human skin dissipates body heat and helps prevent overheating on a hot day or when excess heat is generated by strenuous activity. Evelyn I. Milian - Instructor 11

12 (a) Water can be a solid, a liquid, or a gas at naturally occurring environmental temperatures. At room temperature and pressure, water is a liquid. When water freezes and becomes a solid (ice), it gives off heat, and this heat can help keep the environmental temperature higher than expected. On the other hand when water evaporates, it takes up a large amount of heat as it changes from a liquid to a gas. (b) This means that splashing water on the body will help keep body temperature within a normal range. Evelyn I. Milian - Instructor 12 Emergent Properties of Water: Moderation of Temperature

13 Emergent Properties of Water: Floating of Ice on Liquid Water: Expansion Upon Freezing Insulation of Bodies of Water by Floating Ice Water becomes locked into a crystalline lattice as the temperature falls to 0 C (it freezes). Ice is less dense than liquid water because its more organized hydrogen bonding causes expansion into a crystal formation. (Density is the mass per unit volume of a substance under specified conditions of pressure and temperature). The lower density causes ice to float, which insulates water below, preventing it from freezing, and thus protecting life under the frozen surfaces of lakes and polar seas. Evelyn I. Milian - Instructor 13

Emergent Properties of Water: Expansion Upon Freezing Figure 3.

In ice, each molecule is hydrogen-bonded to four neighbors in a three-dimensional crystal.

water. In other words, ice is less dense than liquid water.

14 Emergent Properties of Water: Expansion Upon Freezing Figure 3.6 Ice: crystalline structure and floating barrier. In ice, each molecule is hydrogen-bonded to four neighbors in a three-dimensional crystal. Because the crystal is spacious, ice has fewer molecules than an equal volume of liquid water. In other words, ice is less dense than liquid water. Floating ice becomes a barrier that protects the liquid water below from the colder air. The marine organism shown here is a type of shrimp called krill. Evelyn I. Milian - Instructor 14

15 Emergent Properties of Water: The Solvent of Life IMPORTANT TERMS Solution Solvent Solute Hydrophilic (hydro = water; philic = loving) A liquid that is a completely homogeneous mixture of two or more substances; it contains dissolved substances. A substance that dissolves another substance; the dissolving agent of a solution. An aqueous solution is one in which water is the solvent. The substance that is dissolved (by the solvent). Having an affinity for water ( water-loving ). Hydrophilic compounds or substances interact readily with water. Polar molecules, with polar covalent bonds (electrons shared unequally, resulting in slight negative and positive charges), attract water molecules and dissolve in water. Hydrophobic (hydro = water; phobic = fearing) Having an aversion to water (tending to coalesce and form droplets in water, water-fearing ). Nonpolar molecules lack polar covalent bonds or have very few; they do not have positive and negative ends. These molecules do not dissolve in water or mix poorly. Evelyn I. Milian - Instructor 15

Emergent Properties of Water: Versatility as a Solvent Water is an unusually versatile solvent because its polar molecules are attracted to charged (ionic) and polar substances.

16 Emergent Properties of Water: Versatility as a Solvent Water is an unusually versatile solvent because its polar molecules are attracted to charged (ionic) and polar substances. These substances (solutes) dissolve in water, resulting in a solution. Examples: sugar, NaCl (sodium chloride, or table salt). Most chemical reactions in organisms involve solutes dissolved in water. A salt dissociates into cations and anions, neither of which is H + or OH --. Evelyn I. Milian - Instructor 16

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18 Emergent Properties of Water: Versatility as a Solvent Figure 3.8 (9 th Edition, Campbell) A water-soluble protein. This figure shows human lysozyme (purple), a protein found in tears and saliva that has antibacterial action. Evelyn I. Milian - Instructor 18

19 Dissociation of Water: Acids and Bases Occasionally, water molecules dissociate and the result is a hydronium ion (H 3 O + ) and a hydroxide ion (OH -- ). The hydrogen atom leaves an electron behind, and what is actually transferred is a hydrogen ion (H + ); so this reaction can be simplified as: H 2 O H + + OH. The dissociation of water is reversible and has important consequences for cells. Hydrogen and hydroxide ions are very reactive and changes in their concentrations can drastically affect a cell s proteins and other complex molecules. Acidity in the human body affects the rate of most chemical reactions and the concentration of many chemicals. In pure water, the concentrations of H + + OH are equal, but adding certain kinds of solutes, called acids and bases, disrupts this balance. Evelyn I. Milian - Instructor 19

20 Acids and Bases Acid Substance that increases the hydrogen ion concentration of a solution. An acid dissociates into one or more hydrogen ions (H + ) and one or more anions (negatively charged ions). An acid is a hydrogen ion donor, or proton donor (because hydrogen ions have a proton, with positive charge). Base A substance that reduces the hydrogen ion concentration of a solution. A base dissociates into one or more hydroxide ions (OH -- ) and one or more cations (positively charged ions). A base is a hydrogen ion acceptor, or proton acceptor (hydroxide ions have a strong attraction for protons). Evelyn I. Milian - Instructor 20

21 Acids and Bases An acid increases the hydrogen ion (H + ) concentration of a solution. For example, when hydrochloric acid (HCl) is added to water, hydrogen ions dissociate from chloride ions: HCl H + + Cl - Strong acids (such as HCl) dissociate completely in water. Weak acids partially dissociate in water (reversibly release and accept back hydrogen ions; notice the arrow in both directions). For example, carbonic acid (H 2 CO 3 ): H 2 CO 3 HCO H + (carbonic acid) (bicarbonate ion) (hydrogen ion) Evelyn I. Milian - Instructor 21

22 Acids and Bases A base reduces the hydrogen ion (H + ) concentration of a solution. Some bases do it directly by accepting H +. For example, ammonia (NH 3 ): NH 3 + H + NH 4 + (ammonium ion) Other bases do it indirectly by dissociating to form hydroxide ions (OH -- ) which then combine with H + in the solution to form water. For example, sodium hydroxide: NaOH Na + + OH -- Strong bases (such as NaOH) dissociate completely in water. Weak bases (such as NH 3 ) partially dissociate in water. Evelyn I. Milian - Instructor 22

23 Salts and Water A salt is any compound that dissolves easily in water and releases ions other than H + and OH --. A salt commonly forms when an acid interacts with a base. HCl (acid) + NaOH (base) NaCl (salt) + H 2 O Hydrochloric acid Sodium hydroxide Sodium chloride Water Na + Cl -- (ionization) Many of the ions release when salts dissolve in fluid are important components of cellular processes. Ions of calcium, sodium, and potassium are involved in the functions of nerve and muscle cells, and help plant cells take up water from the soil. Evelyn I. Milian - Instructor 23

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25 Effects of Changes in ph: The ph Scale ph A measure of hydrogen ion concentration, [H + ]. The ph of a solution is defined as the negative logarithm (base 10) of the hydrogen ion concentration: ph = -- log [H + ] Each ph unit represents a change of 10 times in the H + concentration. ph Scale A ph scale measures the relative acidity or alkalinity of a solution. Extends from 0 to 14 (acidity alkalinity) and is based on the concentration of H + in moles per liter (m/l) (1 mole = 6.02 x molecules; Avogadro s number). neutral ph = 7 (midpoint): the concentrations of H + and OH - are equal. [H + ] = M. Nearly all of life s chemistry occurs near ph 7. log = ( 7) = 7 Acidic solution: Has more H + than OH -- ; ph below 7. Notice that ph declines as [H + ] increases. The lower the ph, the more acidic the solution. Basic (alkaline) solution: Has more OH - than H + ; ph above 7. The higher the ph, the more basic the solution. Evelyn I. Milian - Instructor 25

26 The ph Scale and ph Values of Some Aqueous Solutions ph is a measure of hydrogen ion concentration, [H + ]. The ph scale measures the relative acidity or alkalinity of a solution. Nearly all of life s chemistry occurs near ph 7. Most of your body s internal environment (tissue fluids and blood) is between ph 7.3 and 7.5. Evelyn I. Milian - Instructor 26

27 The ph Scale and ph Values of Some Aqueous Solutions Evelyn I. Milian - Instructor 27

28 Effects of Changes in ph: Buffers Cells must respond fast to even slight changes in ph, because excess H + or OH can alter the functions of biological molecules. A buffer is a substance that helps maintain a constant ph by minimizing changes in the concentrations of H + and OH -- in a solution. Buffers can convert strong acids or bases into weak ones. A buffer works by accepting hydrogen ions from the solution when they are in excess and donating hydrogen ions to the solution when they have been depleted (they absorb excess H + or OH ions). * Buffer systems in the body stabilize or maintain the ph of fluids inside and outside cells almost constant; they resist changes in ph. Example: carbonic acid-bicarbonate buffer system: Response to a rise in ph H 2 CO 3 HCO H + carbonic acid Response to (bicarbonate; Hydrogen ion (H + donor) a drop in ph base: H + acceptor) Evelyn I. Milian - Instructor 28

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31 References Audesirk, Teresa; Audesirk, Gerald & Byers, Bruce E. (2005). Biology: Life on Earth. Seventh Edition. Pearson Education, Inc.-Prentice Hall. NJ, USA. Campbell, Neil A.; Reece, Jane B., et al. (2011). Campbell Biology. Ninth Edition. Pearson Education, Inc.-Pearson Benjamin Cummings. CA, USA. Enger, Eldon D.; Ross, Frederick C.; Bailey, David B. (2007). Concepts in Biology. Twelfth Edition. The McGraw-Hill Companies, Inc. NY, USA. Mader, Sylvia S. (2010). Biology. Tenth Edition. The McGraw-Hill Companies, Inc. NY, USA. Presson, Joelle & Jenner, Jan. (2008). Biology, Dimensions of Life. The McGraw-Hill Companies, Inc. NY, USA. Solomon, Eldra; Berg, Linda; Martin, Diana W. (2008). Biology. Eighth Edition. Cengage Learning. OH, USA. Starr, Cecie. (2008). Biology: Concepts and Applications Volume I. Houston Community College. Thompson Brooks/Cole. OH, USA. Tortora, Gerard J.; Derrickson, Bryan. (2006). Principles of Anatomy and Physiology. Eleventh Edition. John Wiley & Sons, Inc. NJ, USA. Tortora, Gerard J.; Funke, Berdell R.; Case, Christine L. (2010). Microbiology An Introduction. Tenth Edition. Pearson Education, Inc.-Pearson Benjamin Cummings; CA, USA. Evelyn I. Milian - Instructor 31

BIOLOGY 101. CHAPTER 3: Water and Life: The Molecule that supports all Live

BIOLOGY 101. CHAPTER 3: Water and Life: The Molecule that supports all Live BIOLOGY 101 CHAPTER 3: Water and Life: The Molecule that supports all Live The Molecule that Supports all Life CONCEPTS: 3.1 Polar covalent bonds in water molecules result in hydrogen bonding 3.2 Four