3. biological molecules

• water

  • essential for photosynthesis
  • regulates body temperature
• carbohydrates

  • made up of carbon, hydrogen & oxygen
  • ratio of hydrogens to oxygen atoms is 2:1
  • can be classified as simple sugars, double sugars & complex carbohydrates
• simple sugars

  • basic unit of carbohydrate
  • small enough to pass through cell membranes
  • e.g glucose, fructose
• double sugars

  • formed when two single sugars are joined together
  • can be split into two single simple sugar molecules in the presence of an enzyme
  • e.g maltose, sucrose
• Benedict's test

  • test for the presence of reducing sugars (glucose, fructose, maltose)
  • add Benedict's solution a food sample in a test-tube
  • shake the mixture
  • heat the contents in boiling water for 3 minutes
• observations for Benedict's test

  • no reducing sugar - blue
  • traces of reducing sugar - blue to green
  • moderate amt of reducing sugar - blue to yellow/orange
  • large amt of reducing sugar - blue to red
• complex carbohydrates

  • starch
  • cellulose
  • glycogen
• starch

  • storage form of carbohydrates in plants. it is digested to glucose to provide energy for cell activities, when needed.
• cellulose

  • protects plant cells from bursting or injury.
• glycogen

  • branched molecule
  • storage form of carbohydrates in mammals. it is digested to glucose to provide energy for cell activities, when needed.
• examples of carbohydrates

  • bread, rice, noodles
• glycogen and starch are stores of glucose & are suitable as storage materials because they are:

  • insoluble in water
  • large molecules that cannot diffuse through cell membranes
• iodine test

  • test for presence of starch
  • add a few drops of iodine solution to food sample
  • absence of starch - brown
  • presence of starch - brown to blue-black
• functions of carbohydrates

  • provide energy for cell activities
  • form supporting structures (e.g cell wall)
• fats

  • made up of carbon, hydrogen, oxygen
  • contain much less oxygen in proportion to hydrogen
  • fat molecule is made up of glycerol and fatty acid chains
• breakdown of fats

  • broken down into fatty acids and glycerol by lipase
• sources of fats

  • butter, olives, oil
• functions of fats

  • source and store of energy
  • act as an insulating material to prevent excessive heat loss
  • help reduce water loss from skin surface
• ethanol emulsion test

  • test for presence of fats
  • add ethanol to food sample
  • shake contents vigorously
  • add water into the test-tube and shake mixture
  • presence of fats - cloudy white emulsion
• proteins

  • made up of carbon, hydrogen, oxygen, nitrogen
  • each protein molecule is made up of amino acids
  • made up of an amino group, an acid group and a side chain
  • amino acids are linked up by peptide bonds to form a polypeptide. 2 or more polypeptide chains fold to form protein
• functions of proteins: proteins are needed for the synthesis of:

  • antibodies
  • new protoplasm for growth and repair of worn-out cells
• biuret test

  • test for presence of proteins
  • add biuret solution to the food sample
  • shake well and let the mixture stand for five minutes
  • absence of protein - remain blue
  • presence of protein - blue to violet
• sources of fats

  • egg whites, red meat, milk