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Paani (Hindi). maima (Hebrew). amanzi (Zulu). amane (Berber). WATER. jo (Warao). shouei (Chinese). Chapter 3: Water and the Fitness of the Environment. biyo (Somali). wasser (German). mizu (Japanese). su (Turkish). dlo (Haitian). Water 2. Cells are 70-90% water

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Paani (Hindi)

maima (Hebrew)

amanzi (Zulu)

amane (Berber)


jo (Warao)

shouei (Chinese)

Chapter 3: Water and the Fitness of the Environment

biyo (Somali)

wasser (German)

mizu (Japanese)

su (Turkish)

dlo (Haitian)

water 2
Water 2
  • Cells are 70-90% water
  • Three-fourths of Earth’s surface is covered by water
  • Water is the biological medium for life on Earth
  • Water must be present for life (as we know it)
water s polarity 5
Water’s polarity 5
  • Polar – opposite ends of molecule have opposite charges
    • Opposing charges due to oxygen’s electronegativity
      • Oxygen has partial negative
      • Hydrogens have partial positive
  • Water forms H bonds(opposite charges attract)
    • ~15% water molecules in our body are bonded to four partners
four properties of water allowing for life 6
Four Properties of Water Allowing for Life 6
  • Cohesion/Adhesion
  • Moderation of temperature
  • Insulation of bodies of water by floating ice
  • The solvent of life
cohesion 9
Cohesion 9
  • Cohesion - H bonding keeps water molecules close together
  • Makes water a “structured” liquid
  • Adhesion – the clinging of one substance to another
    • Ex. water sticks to sides of a glass
  • Both cohesion and adhesion help water move up from roots to plants to leaves
  • Surface tension – measure of difficult it is to stretch or break the surface of a liquid
    • Water has a high surface tension due to H bonds – almost like a thin film on the surface.
moderation of temperature 10
Moderation of Temperature 10
  • Heat – measure amount of total kinetic energy (cal, kcal, or J)
    • 1 cal = amount of heat needed to raise the temp of 1g of water 1°C
    • 1000 cal = 1 kcal
    • 1 cal = 4.184 J
  • Temperature – measures the intensity of heat due to average kinetic energy of molecules (°C)
  • Specific heat – amount of heat that must be absorbed or lost for 1 g to change its temp by 1 °C
    • Specific heat of water = 1 cal/g/°C


  • Compared to most substances, water’s specific heat is quite high.
  • This means water will change its temp less when it absorbs or gives off heat.
  • Why? H bonds need heat to break and heat is released when bonds are formed.
  • High specific heat allows large bodies of water to absorblots of heat in summer without raising temp too high. In winter, gradual cooling of water helps warm the air.
  • High specific heat helps stabilize ocean temp to better support marine life.


  • Heat of vaporization – quantity of heat a liquid must absorb for 1 g to be converted to a gaseous state
  • Water has a high heat of vaporization (580 cal heat needed to evaporate 1 g water at 25°C) because H bonds must be broken before molecules can change to gas.
    • Evaporative cooling – as liquid evaporates, the surface cools because the hottest molecules leave as gas and cooler molecules are left behind
      • Why sweat? Evaporative cooling in progress!
      • Why do we sweat more on humid days?
insulation of bodies of water by floating ice


Insulation of Bodies of Water by Floating Ice
  • Water is more dense than ice. At 4°C water is at its most dense state, then as it cools to O°C, the molecules freeze. The H bonds keep the water molecules slightly apart (like a lattice) so air pockets form within ice.
  • Lakes, oceans etc. would freeze solid if ice was more dense than water. During the summer, only upper few inches of ocean would thaw making life as we know it impossible (not to mention ice skating and hockey! )
the solvent of life


The Solvent of Life
  • Solvent - dissolving agent in a solution
  • Solute – the substance that is dissolved
  • Aqueous solution – water is the solvent
  • Water can dissolve many substances, but obviously not all!
    • Hydrophilic – likes water
    • Hydrophobic – repel water (nonpolar and nonionic)


  • H+ (protons) occasionally move from one water molecules to another (disassociation).
  • If water loses a H+ then it becomes OH- (hydroxide ion).
  • If water gains a H+ then it becomes H3O+ (hydronium ion).
  • In pure water, the OH- and H+ concentrations are equal.
  • Acid – increases H+ concentrations, nl
  • Base – lots of OH, decreases H+ concentrations


  • Buffers– minimize changes in pH by being able to release or take in H+
  • Buffers keeps blood between 7 and 7.8
acid rain
Acid Rain
  • Acid precipitation – below 5.6
  • Caused primarily by increased levels of sulfur and nitrogen oxides released from the burning of fossil fuels
  • Acid precip can damage lakes, streams, and soil.
  • Acid can make harmful heavy metals more soluble in water.