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Water : An absolute necessity for life

Water : An absolute necessity for life. ¾ of the planet is covered by it Life existed in water 2 Billion years prior to adapting to land 60% of human weight from water 83% of human blood composition Where water exists, life may be found Water is critical to cell biochemistry

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Water : An absolute necessity for life

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  1. Water: An absolute necessity for life ¾ of the planet is covered by it Life existed in water 2 Billion years prior to adapting to land 60% of human weight from water 83% of human blood composition Where water exists, life may be found Water is critical to cell biochemistry Water is critical for photosynthesis Water is the ‘universal solvent’

  2. A generalized water cycle for Earth’s systems

  3. Water’s structure Simple molecular structure with Oxygen bound to 2 Hydrogen atoms by single covalent bonds Electronegativity of O is much greater than H – so the bonds between these atoms are “polar”

  4. Hydrogen bonding:outstanding chemical property of water “The polarity of water impacts water’s chemistry and the chemistry of life…”

  5. Properties of water • Cohesion = • Adhesion = • High specific heat = • High heat of vaporization = • Solid water less dense than liquid = • Has solvent properties =

  6. Fig. 2.14

  7. Water can form ions The covalent bonds of water can break spontaneously to produce H+ and OH- H2O  OH- (hydroxide ion) + H+ (hydrogen ion) At 25° C, one liter of water contains one ten-millionth (10-7) mole of H+ ions A Mole is equal to the weight of a substance (in grams) that corresponds to the atomic mass of the atoms forming the substance H+ has an atomic mass of 1, so a mole of H+ would weigh 1 gram

  8. Water and pH pH = -log [H+] • Therefore, pure water, having 10-7 moles/liter concentration of H+, has a pH of 7.0 • A pH of 7.0 is determined to be “neutral” due to equal concentrations of H+ and OH- ions

  9. pH and logarithms • Note that the pH scale is logarithmic, meaning that a difference of 1 of pH means a 10-fold change in H+ ion concentration • Therefore, a solution having a pH of 3 has 10X more H+ ions than a solution with a pH of 4; 100X more H+ than a solution with a pH of 5

  10. Fig.2.16

  11. Acids Any solution with a pH less than 7.0 The stronger an acid is, the more H+ ions it releases to solution High amounts of H+ ions are caustic = capable of burning, corroding, or destroying living tissue Bases Any solution with a pH greater than 7.0 The stronger a base is, the more OH- or similar ions it releases to solution High amounts of OH- ions are caustic Acids and bases

  12. Buffers help stabilize pH • A buffer is a substance that resists changes in pH • Within organisms, buffers consist of acid-base pairings • In human blood, carbonic acid (H2CO3) serves as a buffer which can split to form bicarbonate ion (HCO3-) and a Hydrogen ion (H+) to aid in stabilizing the pH

  13. Articles on Reserve for Article Review #2 • Taylor, D. 2007. Employment preferences and salary expectations of students in science and engineering. Bioscience. 57: 175-185. • Ostfeld, R.S. et al. 2006. Controlling ticks and tick-borne zoonoses with biological and chemical agents. Bioscience. 56: 383-394. • DeLong, E.F. 2003. A plentitude of ocean life. Natural History. 112: 40-46. • Schmid-Hempel, P. 2003. Fight of the bumblebee. Natural History. 112: 52-59. http://readpac.longwood.edu/search/r?biol+121

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