Water is the biological medium on Earth Fig. 3-1 Water is the biological medium on Earth Most cells are surrounded by water, and cells themselves are about 70–95% water Figure 3.1 Why does the abundance of water allow life to exist on the planet Earth? The abundance of water is the main reason the Earth is habitable All living organisms require water more than any other substance

Water is a ______ Molecule Diagram of a Water Molecule

The polarity of water allows for hydrogen bonding Fig.3.2 The polarity of water allows for hydrogen bonding  – Hydrogen bond  + H —— O  –  + —— H  –  + Figure 3.2 Hydrogen bonds between water molecules  –  +

Unique Properties of Water How do they facilitate an environment for life? Cohesive behavior Ability to moderate temperature Expansion upon freezing Versatility as a solvent Why is this important?

Cohesive Behavior Cohesion: attraction of like molecules ex/___________ Adhesion: attraction of unlike molecules ex?__________ Why is this important?

Adhesion Water-conducting cells Cohesion 150 µm Fig. 3-3 Adhesion Water-conducting cells Direction of water movement Cohesion Figure 3.3 Water transport in plants 150 µm

Fig. 3-4 Figure 3.4 Walking on water Why does water have a high surface tension (measure of how hard it is to break the surface of a liquid)?

Moderation of Temperature Water has a high specific heat (1 cal/g/ºC) - amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC Water absorbs heat from warmer air and releases stored heat to cooler air (slight change in own temperature) Why is this important? How can water’s high specific heat be traced to hydrogen bonding?

Heat of vaporization: is the heat a liquid must absorb for 1 g to be converted to gas Evaporative Cooling: as a liquid evaporates, its remaining surface cools helps stabilize temperatures in organisms and bodies of water

Expansion Upon Freezing Why does ice float?

Hydrogen bonds are stable Hydrogen bonds break and re-form Fig. 3-6 Expansion Upon Freezing Why does ice float? Hydrogen bond Ice Hydrogen bonds are stable Liquid water Hydrogen bonds break and re-form Figure 3.6 Ice: crystalline structure and floating barrier Less Dense: Below ____ More Dense: Above ____ Why is this important?

Versatility as a Solvent Solution: is a liquid that is a homogeneous mixture of substances Solvent: is the dissolving agent of a solution The solute is the substance that is dissolved An aqueous solution is one in which water is the solvent

– – – – – – – – – – – + + + + + + + + + + Na Na Cl– Cl– Fig. 3-7 – Na + + + – – + – – Na + – + + Cl– Cl– + – – + – + – Figure 3.7 Table salt dissolving in water – Hydration Shell

2H2O Hydronium ion (H3O+) Hydroxide ion (OH–) Fig. 3-UN2 H H O O O H O H H H H H 2H2O Hydronium ion (H3O+) Hydroxide ion (OH–)

The dissociation of water molecules has a great effect on organisms (the chemistry of cell) Most biological fluids have pH values in the range of 6 to 8 Buffers: substances that minimize changes in concentrations of H+ and OH– in a solution Teaching the Blood Buffennnnnnnr System using a Demonstration http://vimeo.com/20298747

Figure 3.9 The pH scale and pH values of some aqueous solutions 1 Battery acid Gastric juice, lemon juice 2 H+ H+ H+ H+ OH– 3 Vinegar, beer, wine, cola OH– H+ H+ Increasingly Acidic [H+] > [OH–] H+ H+ 4 Acidic solution Tomato juice Black coffee 5 Rainwater 6 Urine OH– Saliva OH– Neutral [H+] = [OH–] H+ H+ OH– 7 Pure water OH– OH– H+ Human blood, tears H+ H+ 8 Seawater Neutral solution 9 Figure 3.9 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

Human activities such as burning fossil fuels threaten water quality CO2 is released by fossil fuel combustion and contributes to: A warming of earth called the “greenhouse” effect Acidification of the oceans; this leads to a decrease in the ability of corals to form calcified reefs