Water— The Elixir of Life!

Why are we studying water? All life occurs in water inside & outside the cell

Water’s 4 main properties

Chemistry of water Water is polar molecule remember polar covalent bonds + & – poles

H2O molecules form H bonds with each other Water 1st property of water – COHESION/ADHESION occurs due to hydrogen bonding H2O molecules form H bonds with each other + attracted to – creates a sticky (cohesive) molecule

Water Cohesion H bonding between H2O creates cohesion (binding of like molecules) Remember drops of water on a penny? surface tension water is “sticky”

1st Property of Water (cont’d)- Adhesion H2O molecules form H bonds with other substances (adhesion-attraction between different kinds of molecules) Capillary action Ex: Water “climbs up” fiber (paper towel)

How does H2O get to top of tree? Water How does H2O get to top of tree? Example of Capillary Action - Transpiration

2nd Property of Water – Versatility as a solvent H2O is a good solvent due to its polarity Polar H2O molecules surround + & – ions Solvents dissolve solutes creating aqueous solutions In your words What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O?

Hydrophilic Hydrophilic – water loving Some substances have affinity for H2O Look at diagram- polar or non-polar? Ionic What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O?

Hydrophobic Hydrophobic – water hating Some substances do not have affinity for H2O polar or non-polar? non-ionic What dissolves in water easily? polar or non-polar molecules? How about Oxygen? Does that dissolve in H2O? fat (triglycerol)

3rd Property of Water – Expansion upon freezing Most substances are more dense when they are solid. But not water…water expands Therefore, water is less dense as a solid than as a liquid which is why ice floats in water!

Below, hydrogen bonds form a crystal with a loose structure Water Ice floats in water Below, hydrogen bonds form a crystal with a loose structure

Floating ice is the key to life. Water Floating ice is the key to life. Oceans & lakes don’t freeze solid if ice sank… ? surface ice insulates water below seasonal turnover of lakes cycling nutrients

Water 4th property of water – Regulates temperature due to its high specific heat. The heat of vaporization is higher than most liquids making it resistant to change Due to H bonding, H2O resists changes in temperature takes a lot to heat it up takes a lot to cool it down H2O moderates temperatures on Earth

4th property usefulness: Evaporative cooling Water 4th property usefulness: Evaporative cooling Organisms rely on heat of vaporization to remove heat and help resist a change in temperature. From a biological perspective, why is temperature stability important? Think warm blooded

Summary Water is a polar molecule The special properties of water, often due to its hydrogen bonding, make life on Earth possible The chemical behavior of water governs how organisms function

Questions 1. A person with swollen gums rinses his mouth with warm salt water, and the swelling decreases. Which has occurred? A The swollen gums have absorbed the saltwater solution. B The saltwater solution lowers the temperature of the water in the gums. C The salt in the solution has moved against the concentration gradient. D The water in the gums has moved from a high to a low concentration of water.

Question 2 Water is an essential part of all life and considered the universal solvent. Which of the following properties is responsible for this? A. Water forms polar bonds that attract other similar molecules. B. Water forms ionic bonds that attract other similar molecules. C. Water is found in all organic molecules. D. Water forms four covalent bonds.

Question 3 Many mammals control their body temperature by sweating. Which property of water is most directly responsible for the ability to sweat to lower body temperature? A. Water’s change in density when it condenses B. Water’s ability to dissolve molecules in the air C. The absorption of heat by the breaking of hydrogen bonds. D. Water’s high surface tension forms four covalent bonds.