water and life
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WATER AND LIFE. Without water there is no life Cells are 70-90% water Most cells are surrounded by water The abundance of water is the main reason there is life on Earth. I. The Polarity of Water. A. Water is a polar molecule formed by polar covalent bonds - PowerPoint PPT PresentationTRANSCRIPT
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WATER AND LIFE
Without water there is no life• Cells are 70-90% water• Most cells are surrounded by water• The abundance of water is the main reason
there is life on Earth
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I. The Polarity of Water
A. Water is a polar molecule formed by polar covalent bonds• The huge difference in electronegativities
between O and H cause shared e- to spend a greater amount of time closer to O’s nucleus
• OH bonds and NH bonds are polar covalent• O side is slightly negative while H side is
slightly positive
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B. Water forms hydrogen bonds• Weak attraction between positive H and negative
O between water molecules or any molecules with OH and NH
http://programs.northlandcollege.edu/biology/biology1111/animations/hydrogenbonds.html
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II. Water’s 4 Emergent Properties that Contribute to Life
• Cohesive nature• Ability to moderate temperature• Expansion upon freezing• Versatile solvent
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A. Cohesion and adhesion
• Cohesion: water molecules stick together thru hydrogen bonds
• Adhesion: water molecules and other polar molecules (like cellulose in cell walls)
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1. Role in water transport in plants
• As water evaporates out of open stomata in plants (transpiration), cohesion and adhesion pull water up plant xylem
https://www.youtube.com/watch?v=mc9gUm1mMzc
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2. Surface tension
• Due to cohesion, the surface of water is hard to break
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2. Temperature Moderation
• Water absorbs heat warmer air and releases heat to cooler air without changing much in temperature because it has a high specific heat
• Specific heat: amount of heat that must be absorbed or released in order to change the temp by 1o C
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• Water’s high specific heat is due to hydrogen bonding–Heat is absorbed when hydrogen bonds
break–Heat is released when hydrogen bonds
form
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• Evaporative cooling and water–Water has a high heat of vaporization:
amount of heat needed to transform 1g of liquid water to water vapor•Heat increases molecular motion•Hydrogen bonds limit molecular motion•Much heat must be added to cause water
to evaporate
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C. Ice Floats
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• What do you notice about water molecules in liquid water and ice?
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• If ice sank all bodies of water would eventually freeze solid making life impossible
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D. Versatile Solvent
• Water can dissolve ionic compounds and large molecules with ionic and polar regions by forming hydration shells around them
• https://www.youtube.com/watch?v=EBfGcTAJF4o
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Hydrophilic: water lovingHydrophobic: water hating
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III. Acids Bases pH and Buffers
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• In pure water [H+] = [OH-]• Adding acids and bases to water alters this• pH measures how acidic or basic a solution is• acid increases [H+] while base decreases [H+]• [H+][OH-] = 10-14
• What is [H+] and [OH-]?• pH = -log[H+]• in pure water, pH = -(-7) = 7
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Buffers are substances that minimize changes in pH by reversibly combining with H+