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WATER AND LIFE

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

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WATER AND LIFE

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  1. 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

  2. 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

  3. 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

  4. II. Water’s 4 Emergent Properties that Contribute to Life • Cohesive nature • Ability to moderate temperature • Expansion upon freezing • Versatile solvent

  5. A. Cohesion and adhesion • Cohesion: water molecules stick together thru hydrogen bonds • Adhesion: water molecules and other polar molecules (like cellulose in cell walls)

  6. 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

  7. 2. Surface tension • Due to cohesion, the surface of water is hard to break

  8. 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

  9. Water’s high specific heat is due to hydrogen bonding • Heat is absorbed when hydrogen bonds break • Heat is released when hydrogen bonds form

  10. 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

  11. C. Ice Floats

  12. What do you notice about water molecules in liquid water and ice?

  13. If ice sank all bodies of water would eventually freeze solid making life impossible

  14. 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

  15. Hydrophilic: water loving Hydrophobic: water hating

  16. III. Acids Bases pH and Buffers

  17. 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

  18. Buffers are substances that minimize changes in pH by reversibly combining with H+

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