OCR A LEVEL BIOLOGY - Biological Molecules

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Last updated 5:05 PM on 8/1/26
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6 Terms

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Structure of water molecules?

  • Molecule of water = one atom of oxygen joined to 2 atoms of hydrogen by shared electrons

  • Shared negative electrons from the hydrogen are pulled towards the oxygen atom → makes one side of each hydrogen atom slightly positively charged

  • Unshared negative electrons on the oxygen atom gives it a slight negative charge

  • Water is now a polar molecule - has both partially negative + positive charges on either side

<ul><li><p>Molecule of water = one atom of oxygen joined to 2 atoms of hydrogen by shared electrons </p></li><li><p>Shared negative electrons from the hydrogen are pulled towards the oxygen atom → makes one side of each hydrogen atom slightly positively charged</p></li><li><p>Unshared negative electrons on the oxygen atom gives it a slight negative charge</p></li><li><p>Water is now a polar molecule - has both partially negative + positive charges on either side </p></li></ul><p></p><p></p>
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Functions of water

  • Reactant → chemical reactions

  • Solvent → substances can dissolve + most biological reactions occur in solution (e.g. cytoplasm)

  • Transports substances - (liquid + solvent) → oxygen in red blood cells, glucose

  • Aids with temperature control → high specific heat capacity + high latent heat of evaporation

  • Habitat → organisms can survive + reproduce in it

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Relation of water’s structure to its properties/functions

Hydrogen bonds

  • provide water with a high specific heat capacity

    • energy required to raise temperature by 1 gram of a substance by 1C

    • H bonds between water molecules can absorb a lot of energy → water has a high specific heat capacity → takes a lot of energy to heat up

    • Water’s temperature does not rapidly fluctuate → makes it a good habit → acts stable - enzymes can work, organisms will not suffer from thermal shock (breaking of living organism due to change in temperature)

  • provide water with a high latent heat of evaporation

    • Lots of energy required to break hydrogen bonds between water molecules

    • Lots of water is used up when water evaporates

    • Useful for living organisms → water can cool organisms through sweating - takes away heat

Polarity

  • makes water molecules cohesive → attracted to each other → allowing it to flow - important for transporting substances → especially in plant stems as part of transpiration stream

  • makes water a good solvent → ionic substances

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What are polymers?

Chain of monomers (small, simple molecules) bonded together

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What are the monomers that make up carbohydrates called?

Monosaccharides

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