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Biochemistry Water and the Fitness of the Environment PowerPoint Presentation
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Biochemistry Water and the Fitness of the Environment

Biochemistry Water and the Fitness of the Environment

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Biochemistry Water and the Fitness of the Environment

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  1. Biochemistry Water and the Fitness of the Environment

  2. Water: The molecule that supports life on this planet! • Water is the biological medium for all life on Earth • All living organisms require water more than any other substance

  3. FOUR Emergent Properties of water contribute to Earth’s suitability for life • Water’s cohesive & adhesive behavior • Water’s ability to moderate temperature • Water’s expansion upon freezing • Water’s versatility as a solvent.

  4. What causes water molecules to both cohere and adhere? • Yep! Our good buddy the intermolecular force (IMF) named hydrogen bonding • Cohesion is when water molecules stick to each other. • Adhesion is when water molecules stick to some other type of substance like plant cell walls. Animation by scrolling over image

  5. What causes water molecules to both cohere and adhere? • Surface tension is a measure of how hard it is to break the surface of a liquid. • Surface tension is a consequence of cohesion. What causes it? Go ahead, guess! Hydrogen bonding, yet again!

  6. How does water moderate temperature? • Water has a high heat capacity. • Heat capacity is the amount of heat required to raise 1 gram of water by 1o Celsius (1 calorie = 4.184 J) • What does that mean? It means water can absorb large quantities of heat without much change in its own temperature, thus it’s a good thermo regulator. • But, why? Guess again!

  7. It’s a 2-way street! • Water’s high specific heat can be traced to hydrogen bonding (IMFs) • Heat is absorbed when hydrogen bonds break • Heat is released when hydrogen bonds form • The high specific heat of water minimizes temperature fluctuations to within limits that permit life

  8. Ever sweat? Ever perspire? • Evaporation is transformation of a substance from liquid to vapor • Heat of vaporization is the heat a liquid must absorb for 1 g to be converted to vapor • As a liquid evaporates, its remaining surface cools, a process called evaporative cooling • Evaporative cooling of water helps stabilize temperatures in organisms (sweating, panting, etc.)and bodies of water

  9. Water is a freak! It expands upon freezing! • Ice floats in liquid water because hydrogen bonds in ice are more “ordered” forming a hexagonal shape with a hole in the middle, making ice lessdense. • Water reaches its greatest density at 4°C, which is excellent news if you’re a fish! • If ice sank, all bodies of water would eventually freeze solid, making life impossible on Earth

  10. Water is a freak! It expands upon freezing! Hydrogen bond Liquid water: Hydrogen bonds break and re-form Ice: Hydrogen bonds are stable

  11. Water’s Versatility as a Solvent • A solutionis a liquid that is a homogeneous mixture of substances • A solvent is the dissolving agent of a solution or “dissolver” • The solute is the substance that is dissolved or “disolvee” • An aqueous solution is one in which water is the solvent

  12. Water’s Versatility as a Solvent • Water is a versatile solvent due to its polarity, which allows it to form hydrogen bonds easily. • When an ionic compound is dissolved in water, each ion is surrounded by a sphere of water molecules called a hydration shell

  13. Water’s Versatility as a Solvent • Water can also dissolve compounds made of nonionic polar molecules • Even large polar molecules such as proteins can dissolve in water if they have ionic and polar regions

  14. Hydrophilic vs. Hydrophobic • A hydrophilic substance is one that has an affinity for water • A hydrophobic substance is one that does not have an affinity for water; “fears water” • Oil molecules are hydrophobic because they have relatively nonpolar bonds • A colloid is a stable suspension of fine particles in a liquid (like milk—fat suspended in water—Yummy!)

  15. Acids, Bases and Buffers. Oh, my! ACIDIC AND BASIC CONDITIONS AFFECT LIVING ORGANISMS • A bonded hydrogen atom within a water molecule can shift betweentwo water molecules (from one molecule to the other).

  16. Acids, Bases and Buffers. Oh, my! • The hydrogen atom leaves its electron behind and is transferred as a proton, or hydrogen ion (H+) • The molecule with the extra proton is now a hydronium ion (H3O+), though it is often represented as H+ • The molecule that lost the proton is now a hydroxide ion (OH–)

  17. Acids, Bases and Buffers. Oh, my! • Though statistically rare, the dissociation of water molecules has a great effect on organisms • About 2 in every billion water molecules exist as H+ and OH– • Changes in concentrations of H+ and OH– can drastically affect the chemistry of a cell

  18. Acids, Bases and Buffers. Oh, my! • Concentrations of H+ and OH– are equal in pure water • Adding certain solutes, called acids and bases, modifies the concentrations of H+ and OH– • Biologists use something called the pH scale to describe whether a solution is acidic or basic (the opposite of acidic; also known as alkaline)

  19. Acids, Bases and Buffers. Oh, my! Simply put, • An acid is any substance that increases the H+ concentration of a solution • A base is any substance that reduces the H+ concentration of a solution Bleach

  20. Acids, Bases and Buffers. Oh, my! Buffers • The internal pH of most living cells must remain close to pH 7 • Buffers are substances that RESIST changes in concentrations of H+ and OH– in a solution, therefore they RESIST a change in pH • Most buffers consist of an acid-base pair that reversibly combines with H+

  21. The pH Scale • An acid is any substance that increases the H+ concentration of a solution • A base is any substance that reduces the H+ concentration of a solution • The scale was designed to compare WEAK acids and bases.

  22. The pH Scale • In any aqueous solution at 25°C the product of H+ and OH– is constant and can be written as the autoionization constant of water • The pH of a solution is defined by the negative logarithm of H+ concentration, written as • For a neutral aqueous solution, [H+] is 10–7, so [H+][OH–] = 10–14 pH = –log [H+] pH = –(–7) = 7

  23. The pH Scale • Acidic solutions have pH values less than 7 • Basic solutions have pH values greater than 7 • Most biological fluids have pH values in the range of 6 to 8

  24. The pH Scale • Each increase (toward more acidic or more basic – away from 7 in either direction) on the pH scale increases by a factor of 10. So an acid with a pH of 2 is 100 times more acidic than an acid with a pH of 4.

  25. Created by: René McCormick National Math & Science Dallas, TX