water and carbohydrates


Functions of water

  • Solvent - Because water is polar, the slightly positive end will attract the negative ions and the positive end to the negative ions so the ions will dissolve. Means ions can be easily transported around the body
  • High specific heat capactiy - The energy needed to raise the temperature of 1g of a substance by 1 degree. Water remains at a fairly constant temperature, essential for life to survive
  • Ice is less dense than water - Water molecules are held further apart in ice so ice floats on water, which insulates the water and prevents it freezing completely meaning living things can survive below ice
  • High latent heat of evaporation - The energy needed to break the hydrogen bonds between water molecules. Good for cooling things - when sweat evaporates, the skin cools
  • Cohesive - The attraction between molecules of the same type. Helps water to flow so good for transporting substances
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Structure of water

  • Covalent bonds - Hydrogen and oxygen joined by covalent bonds
  • Water is a polar molecule - the hydrogen is slightly positive and the oxygen is slightly negative
  • Hydrogen bonds - the slightly negative oxygen attracts the slightly positive hydrogen
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Macromolecules and polymers

  • Macromolecules - Complex molecules with a large molecular mass e.g. proteins, carbohydrates and lipids
  • Monomers - Simple molecular units e.g. monosaccharides and amino acids
  • Polymers - Long chains of monomers joined together
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Making and breaking polymers

Making polymers:

  • Condensation reaction
  • Chemical bond forms
  • Releases a molecule of water

Breaking polymers:

  • Hydrolysis reaction
  • Chemical bond breaks
  • Uses a molecule of water
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What are carbohydrates:

  • Polymers
  • Made up of carbon, hydrogen and oxygen
  • The monomers that make up carbohydrates are monosaccharides

Formation of polysaccharides:

  • Condensation reaction between hydrogen atom and a hydroxyl group
  • Glycosidic bond forms
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  • 6 carbon atoms
  • 2 types - alpah and beta
  • Soluble - easily transported
  • Energy source in plants and animals


  • 5 carbon atoms
  • Sugar component of RNA nucleotides
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  • Energy storage in plansts
  • Insoluble - doesn't cause water to enter cells by osmosis
  • Amylose - long, unbranched chain of alpha glucose, coiled, compact
  • Amylopectin - long, branched chain of alpha glucose, can be broken down easily - releasing glucose


  • Energy storage in animals
  • Very branched chains of alpha glucose
  • Can be broken down easily, releasing glucose quickly
  • Compact


  • Component of cell walls
  • long, unbranched chains of beta glucose
  • Chains joined together by hydorgen bonds to form strong fibres - good for support
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