8/8/2019 ENDURING UNDERSTANDING SYI-1 Living systems are organized in a hierarchy of structural levels that interact. 1.1 Structure of Water and Hydrogen Bonding SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. Living systems depend on properties of water that result The subcomponents of biological molecules and their from its polarity and hydrogen bonding. sequence determine the properties of that molecule. SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Polarity The hydrogen bonds between water molecules result in • Oxygen more electronegative than hydrogen cohesion, adhesion, and surface tension. • Electrons spend more time closer to Oxygen • Uneven charge on molecule makes it polar. • Polarity creates hydrogen bonds • H-bonds are responsible for emergent properties of water 1 8/8/2019 SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Cohesion – Adhesion • Hydrogen bonds hold water molecules • H- bonds hold water molecules to another substance together • Adhesion to solid surfaces creates capillarity • Creates Surface tension • Capillarity allows water to move against gravity – Measurement of the difficulty to break • Plants can grow tall or stretch the surface of a liquid – Must break the H-bonds to break the tension SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – High Specific Heat • Amount of heat absorbed or lost – Heat of Fusion to change temperature by 1oC • Quantity of heat required to convert unit mass of a liquid into a solid • Water’s high specific heat is due • Temp of surrounding rises to H-bonds • Keeps temperatures constant • Creates evaporative cooling • Regulates temp in standing bodies of water • Prevents overheating • Temp of surrounding drops SYI-1.A Explain how the properties of water that SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect result from its polarity and hydrogen bonding affect its biological function. its biological function. – Density - Versatile Solvent • Less dense as solid than liquid • Breaks up ionic compounds • Due to hydrogen bonding • Dissolves other polar Water molecules • Crystalline lattice keeps Ice molecules at a distance • Creates hydrophylic and hydrophobic interactions • Water is most dense at 4oC= ice floats with different molecules • Keeps free water on earth 2 8/8/2019 SYI-1.A Explain how the properties of water that result from its polarity and hydrogen bonding affect its biological function. – Acid/Base & pH • Water dissociates into a hydrogen ion (hydronium ion) and a hydroxide ion 1. Acids release H + ions 2. Bases release OH- ions • pH Scale 1. “power/percent of hydrogen” 2. measures H+ concentration 3. Each step is a 10x increase • Buffers 1. Substances that accepts or donates H+ ions 2. Minimize change in pH • Acid Rain 1. Causes deforestation by changing soil pH 2. Destroys life in water 3.