CH3 - 1 CH3 Water The Molecule That Supports All of Life...

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Unformatted text preview: 1 CH3: Water The Molecule That Supports All of Life • All living organisms require water more than any other substance • Most cells are surrounded by water, and cells themselves are about 70–95% water The polarity of water molecules • The water molecule is a polar molecule : The opposite ends have opposite charges • Polarity allows water molecules to form hydrogen bonds with each other Fig. 3-2 Hydrogen bond δ – H δ + H O — — δ + δ + δ + δ – δ – δ – 2 Four properties of water contribute to Earth’s fitness for life • Four of water’s properties that facilitate an environment for life are: – Cohesive behavior (including adhesion & surface tension) – Ability to moderate temperature – Expansion upon freezing – Versatility as a solvent Cohesion • Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion • Cohesion helps the transport of water against gravity in plants • Adhesion is an attraction between different substances, for example, between water and plant cell walls • Surface tension is a measure of how hard it is to break the surface of a liquid • Surface tension is related to cohesion 3 Moderation of Temperature • Water absorbs heat from warmer air and releases stored heat to cooler air • Water can absorb or release a large amount of heat with only a slight change in its own temperature Heat and Temperature • Kinetic energy is the energy of motion • Heat is a measure of the total amount of kinetic energy due to molecular motion • Temperature measures the intensity of heat due to the average kinetic energy of molecules Water’s High Specific Heat • DEFINITION: The specific heat of a substance is the amount of heat that must be absorbed or lost for 1 g of that substance to change its temperature by 1ºC...
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CH3 - 1 CH3 Water The Molecule That Supports All of Life...

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