Biochemistry Water and the Fitness of the Environment

Objec&ves: SWBAT explain the four emergent proper&es of water. How do the unique proper&es of water allow life to exist on earth? 2

Proper&es of Water Lecture 1 Campbell AP 8 th Ed. Ch. 3

DO NOW: Why does ice float on water?

Why is water so special?

Why is water so special? EssenEal to all life But why? We ll find out today.

But HOW is water so special? Hydrogen bonding!!!

The Water Molecule H20 Two hydrogen atoms + 1 oxygen atom

The Water Molecule Water is a POLAR molecule One end is slightly posi&vely charged (hydrogen), one end is slightly nega&vely charged (oxygen) Kind of like a magnet!

CHARGES IN A POLAR MOLECULE

Hydrogen Bonding A^rac&on between posi&ve H and nega&ve O between two different water molecules

Hydrogen Bonding Results in proper&es of: Cohesion A^rac&on of water to each other Adhension Water s&cks to another surface with a charge High surface tension Measure of how difficult it is to stretch or break the surface of a liquid

(Review: Types of bonding) HYDROGEN Weakest A^rac&on of hydrogen atom and electronega&ve atom Think Velcro (easy to break apart)

(Review: Types of Bonding) IONIC Stronger A^rac&on of two ions of opposite charges Think marriage (hard to break apart) Example:

(Review: Types of Bonding) COVALENT Strongest Share electrons Think Siamese twins (very hard to break apart) Example:

PROPERTIES OF WATER Due to hydrogen bonding

KP1: Two proper&es of water support life on earth: 1) polar covalent bonds 2) hydrogen bonds Water is the biological medium for all life on Earth All living organisms require water more than any other substance 17

KP1: Two proper&es of water support life on earth: 1) polar covalent bonds 2) hydrogen bonds 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 18

KP2: The four emergent proper&es of water are: 1. Water s cohesive & adhesive behavior 2. Water s ability to moderate temperature 3. Water s expansion upon freezing 4. Water s versa&lity as a solvent. 19

1) Water s cohesive & adhesive behavior What? Cohesion is when water molecules s3ck to each other. Adhesion is when water molecules s3ck to some other type of substance like plant cell walls. How? Water molecules H-bond with one another Being polar, water is Anima&on by scrolling over image a^racted to other polar 20 molecules

Cohesion Water molecules s&ck to other water molecules Causes water to form drops Achieved by HYDROGEN BONDING

Adhesion S&cking of water molecules to other substances Aids in movement of water up the xylem of a plant (transpira&on)

1) Water s cohesive & adhesive behavior Example: Surface tension is a measure of how hard it is to break the surface of a liquid. Surface tension is a consequence of cohesion. What causes it? Go ahead, guess! Hydrogen bonding, yet again! 23

Surface Tension Water has very high surface tension Related to cohesion and hydrogen bonding Observe: dropping water on a penny Observe: animals able to walk on water

Surface Tension

2) Water s ability to moderate temperature What? Water has a high heat capacity: water can absorb large quan&&es of heat without much change in its own temperature. Heat capacity is the amount of heat required to raise 1 gram of water by 1 o Celsius (1 calorie = 4.184 J) How? Heat causes movement. Water resists movement because H-bonds hold water molecules together. 27

2) Water s ability to moderate temperature SIDENOTE: It requires energy to break bonds. It releases energy when bonds form. 28

High Specific Heat

High Specific Heat Water takes a lot of heat to change temperature (hydrogen bonds in water need to be broken first) Therefore, it can absorb large amount of heat from the environment without a large change in temperature Moderates climate for life on Earth (both terrestrial and marine) Places on the coast have more moderate temperature than places not surrounded by water

High Specific Heat Moderates temperature and climate E.g., Montana (leq) vs. Sea^le (right) are same la&tude Heat capacity of water is higher than heat capacity of land!

2) Water s ability to moderate temperature Example: Humid air can hold more heat because water has a high specific heat. Large bodies of water absorb heat from warmer air and release stored heat to cooler air. 32

Evapora&ve Cooling

Evapora&ve Cooling Allows organisms to regulate their temperature by swea&ng Prevents us from overhea&ng Requires high amount of energy to evaporate Helps moderate Earth s climate Solar heat absorbed

Ever sweat? Ever perspire? Example (Con t): Evapora&on is transforma&on of a substance from liquid to vapor Heat of vaporizaeon is the heat a liquid must absorb for 1 g to be converted to vapor As a liquid evaporates, its remaining surface cools, a process called evaporaeve cooling Evapora&ve cooling of water helps stabilize temperatures in organisms (swea&ng, pan&ng, etc.) and bodies of water 35

3) Expansion upon freezing Ice: stable hydrogen bonds Liquid water: transient hydrogen bonds

Water is a freak! It expands upon freezing! Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Hydrogen bonds are stable

Ice Floats

Ice Floats Most substances are more dense in their solid state than in their liquid state Hydrogen bonding results in three-dimensional matrix of molecules that actually decreases density Hydrogen bonds keep molecules at arms length

Water is a freak! It expands upon freezing! What? Water takes up more room as it freezes. Since it still weighs the same, this means its density decreases as it freezes. How? Hydrogen bonds in ice are more ordered forming a hexagonal shape with a hole in the middle, making ice less dense. Example: If ice sank, all bodies of water would freeze solid, making life impossible on Earth

Ice Floats Important because.. If ice sank, eventually all bodies of water would freeze solid; ice is like a blanket on top of water We would be a frozen planet

Good Solvent Very versa&le Due to polarity of water molecule Many substances dissolve in it Dissolving means separa&ng a substance into its anions and ca&ons

4) Water s versa&lity as a solvent Solvent = dissolver in a solution Solute = substance dissolved or disolvee Solution = liquid that is a homogeneous mixture of substances Aqueous solution = solution where water is the solvent 43

4) Water s versa&lity as a solvent What? Water dissolves many things by attracting their electrons. How? Water is a polar molecule so it attracts to negatively and positively charged solutes. Example: Ionic compounds in water, are surrounded by a sphere of water molecules called a hydration shell 44

4) Water s versa&lity as a solvent Example: 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 45

4) Water s versa&lity as a solvent A hydrophilic substance is one that has an affinity for water A hydrophobic substance is one that does not have an affinity for water; fears water Oil molecules are hydrophobic because they have relatively nonpolar bonds A colloid is a stable suspension of fine particles in a liquid (like milk fat suspended in water Yummy!) 46

Good Solvent For example, Na + Cl - (table salt) H (+) atoms in water a^racted to Cl (-) anions in salt O (-) atoms in water a^racted to Na (+) ca&ons in salt Water molecules separate the Na and Cl atoms

Good Solvent For example, sugar (C 12 H 22 O 11 ) Sucrose has a lot of O-H bonds, which are polar Water separates the sucrose molecule by breaking hydrogen bonds

Water makes it possible to break down larger molecules If they weren t broken down, they wouldn t be able to pass through cell membrane (and therefore would not be usable) Good Solvent

In Summary: Water: Makes life possible on earth Keeps the planet at a moderate temperature suitable for life High Specific Heat Ice floats Breaks down molecules so that they can cross our cell membranes and be used by our cells Good solvent Allows for thermoregula&on in our bodies High Specific Heat Evapora&ve cooling

VIDEO WATER (Bozeman) h^ps://www.youtube.com/watch? v=ioovx0jmhj4 Mp4 downloaded

CLASSWORK STUDENT ACTIVITY ON WATER: Work on Loose-leaf paper in your binders. Water is a molecule. The is the substance that is present in the greatest amount, and is the substance that the solute. The is the substance that dissolves. The a^rac&on among molecules of the same substance is called. The a^rac&on among molecules of different substances is called. Hydrogen bonds present in water give it a specific heat. Water is a very good because it is a polar molecule. Draw the structure of hydrogen bonds in water.

CLASSWORK STUDENT ACTIVITY ON WATER: Work on Loose-leaf paper in your binders. Water is a polar_ molecule. The _solvent_ is the substance that is present in the greatest amount, and is the substance that dissolves the solute. The solute is the substance that dissolves. The a^rac&on among molecules of the same substance is called cohesion_. The a^rac&on among molecules of different substances is called _adhesion. Hydrogen bonds present in water give it a high_ specific heat. Water is a very good solvent because it is a polar molecule.

hydrogen bond Ionic bonds covalent bonds solu&on solvent solute cohesion adhesion surface tension specific heat Vocabulary

INDEPENDENT PRACTICE Draw the structure of water and explain why it is called a polar molecule. Explain with a diagram how the polar nature of water helps to make it a good solvent.

EXIT TICKET Discuss how the proper&es of water help make life possible on earth. Class group discussion.