BY1 Biological Molecules

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Biological Importance of Water

Water molecules are polar and they have many uses:
- solvent            - metabolite            - support            - transportation        - thermo-regulation 

Hydrogen atoms are covalently bonded to the oxygen atoms - 2 atoms sharing electrons 

(http://www.school-for-champions.com/chemistry/images/polar_molecules-h2o.gif)

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Biological Importance of Water

Oxygen pulls shared electrons towards themselves -- through covalent bonds -- as it has more protons. Water molecules becomes polar 

This difference in charge results in each water molecule having a net dipole moment. The net dipole on each water molecule produces an attraction. This attraction is called a hydrogen bond.

(http://www.fastbleep.com/assets/notes/thumb/10930_1.jpg)

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Biological Importance of Water

Hydrogen BondsThey occur as a result of an attraction between water molecules due to their net dipole moments.

  • They are relatively strong when in large numbers 
  • Able to pull water molecules closer together so makes it harder to separate -- high boiling point
  • They are responsible for the characteristic crystal lattice structure of ice
  • (http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/graphics/water.gif)
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Biological Importance of Water- water as a solvent

Water as a Solvent

> Polar substances like sugar and salt are hydrophilic and are soluble 
> Non-polar such as oil are hydrophobic and insoluble 

(http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/graphics/nacl2.gif)

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Biological Importance of Water- water as a metabol

Water as a Metabolite

Water is used in many metabolic reactions like in photosynthesis, released in respiration and water helps move reactants around cells. 

(http://www.biospectrumasia.com/IMG/291/59291/thermo-fisher-nus-study-plant-metabolite-effects-on-urban-water-systems-262x174.jpg)

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Biological Importance of Water - thermal propertie

Thermal Properties

High heat capacity
A large amount of energy is needed to break the hydrogen bonds so molecules can move faster

             ------> This means that ocean temperatures remain stable so endotherms
                         can 
maintain a constant body temperature

(http://ak0.picdn.net/shutterstock/videos/1307254/preview/stock-footage-sunrise-shines-on-calm-ocean-surface-while-small-waves-roll-on-a-sandy-beach.jpg)

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Biological Importance of Water - thermal propertie

Thermal PropertiesLarge latent heat of vaporisation

  ---> Large amount of heat must be absorbed to turn into water vapour. Heat needed to break the hydrogen bonds in order for evaportion - this produces a large cooling effect due to evaporation

  ---> Cooling effect contributes to the stability of lake and pond temperatures - prevents overheating in plants as they transpire and animals as they sweat. 

(http://alcheme.tamu.edu/wp-includes/images/icc2/LatentHeatofFusion.jpg)

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Biological Importance of Water ice floats

Ice Floats

At 0c water must lose a large amount of energy before it forms ice crystals
    - Crystalline lattice forms as water reaches 0c  
    - Each hydrogen molecule bonded to maximum of 4 others
    - Bonds far enough apart makes ice 10% less dense than water
    - Ice insulates liquid below preventing whole lakes/ponds etc from freezing over (maintain life)

(http://content-img.experienceproject.com/1339432654T4v05v.gif)

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