Water

Water

1. Hydrogen bonding in water

   • H2O molecules polar and linked by hydrogen bonds
   • covalent bond 2H, O
   • H partial positive; O partial negative
   • bent; poles are 2H and O
   • positive and negative ions attract and form ionic bonds
   • water - partial charge; less attraction, hydrogen bond
   • intermolecular force rather than bond
   • slightly positive pole weakly attracted to slightly negative pole

2. Properties of water

   • Cohesive properties
     • binding of two molecules of the same type
     • due to hydrogen bonding
     • useful for water transport in plants
     • xylem sucks up water at low pressure
   • Adhesive properties
     • hydrogen bonds between water and other polar molecules
     • useful in leaves
     • water adheres to cellulose in cell wall
     • water absorbed from nearest xylem in case of evaporation from leaf via air network spaces to keep walls moist for CO2 absorption
   • Thermal properties
     • High specific heat capacity
       • H bonds restrict motion so high heat required to break them
       • relatively large amount of energy needed
       • thermally stable habitat
     • High latent heat of vaporisation
       • lots of energy needed for evaporation to break H bonds
       • Good evaporative coolant
     • High boiling point
       • 100 degrees Celsius for same reason
   • Solvent properties
     • polarity prevents molecules from clumping
     • dissolves molecules
     • cytoplasm - complex mixture of dissolved substances

3. Hydrophilic and hydrophobic

   • hyrophilic = water loving
     • substances that dissolve in water like glucose, sodium and chloride ions
     • substances that water adheres to such as cellulose
   • hydrophobic = water "fearing"
     • insoluble in water
     • non polar and no charge
     • all lipids such as fats and oils
   • forces that cause non polar substances to form groups = hydrophobic interactions

4. Comparing water and methane

   • methane = waste product of anaerobic respiration where oxygen is lacking by certain prokar.
   • methanogenic prokar. live in swamps, wetlands, animal guts, waste dumps
   • methane fuel & greenhouse gas
   • both small molecules linked by single covalent bonds
   • water polar, forms H bonds methane non polar, cannot form H bonds

5. Cooling the body with sweat

   • sweat carried via narrow ducts to skin surface where spread out and released
   • heat on skin used to evaporate sweat and cool blood
   • solutes in sweat left on skin
   • controlled by hypothalmus in brain

6. Transport in blood plasma

   • Sodium chloride
   • amino acids
   • Glucose
   • Oxygen
   • Fat molecules
   • Cholestrol

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