food

• Function of Food

  • A source of energy
  • To make chemicals for metabolism
  • For growth and repair
• Common elements found in all foods

  • Carbon
  • Hydrogen
  • Oxygen
  • Sulfur
  • Nitrogen
• Common elements found in salts

  • Sodium
  • Magnesium
  • Chlorine
  • Potassium
• Trace Elements

  • Iron
  • Copper
  • Zinc
• Carbohydrates


  Consist of elements: carbon, hydrogen and oxygen
• Types of Carbohydrate


  • Monosaccharide (Smallest, one sugar unit e.g. glucose, fructose)
  • Disaccharide (Two monosaccharides connected e.g. maltose, lactose)
  • Polysaccharide (Largest, many monosaccharides connected e.g. starch, cellulose, glycogen)
• Monosaccharides and some disaccharides

  • Are called reducing sugars
• Starch


  Found in ground tissue of plants
• Cellulose

  Found in plant cell walls
• Glycogen

  Found in the liver
• Structural carbohydrate

  Cellulose (plant cell walls)
• Carbohydrate ratio


  • Ratio of hydrogen to oxygen is 2:1
  • General formula: Cx(H2O)y
• Lipids


  • Consist of oils, fats and steroids
  • Oils are liquids at room temperature
  • Fats are solid at room temperature
  • Contain the elements carbon, hydrogen and oxygen
• Functions of Fat

  • Heat insulation
  • Energy store
• Phospholipids


  • One glycerol
  • Two fatty acids
  • One phosphate head
  • Found: Cell membranes
• Triglyceride


  • One glycerol
  • Three fatty acids
  • Found: Fatty foods
• Proteins


  • Contain the elements carbon, hydrogen, oxygen and nitrogen
  • Sometimes contains sulphur (non-metallic)
• Amino acid


  The smallest unit of a protein
• Common amino acids found in proteins

  • 20
• Each different sequence of amino acids produces a different protein
• Each protein is folded to take up 3D functional shape
• Peptide bond


  The bond between amino acids
• Protein structures


  • Peptides
  • Polypeptides
  • Proteins
• Structural (fibrous) protein


  • Keratin in hair, nails
• Metabolic protein

  • Enzymes and hormones
• Sources of protein

  • Lean meat
  • Fish
  • Egg white
• Vitamins


  • Water-soluble Vitamin: Vitamin C
  • Fat-soluble Vitamin: Vitamin D
• Vitamins


  Required in only small amounts in the diet for health, cell production and tissue growth
• Vitamin C

  • Water-soluble
  • Citrus fruits
  • Skin and gums rot (Deficiency disease: Scurvy)
• Vitamin D

  • Fat-soluble
  • Milk, eggs, sunshine
  • Bones begin to bend (Deficiency disease: Rickets)
• Minerals required by plants

  • Calcium (Ca)
  • Magnesium (Mg)
• Calcium (Ca) for plants


  • Helps cell walls to attach to one another
  • Source: The soil
• Magnesium (Mg) for plants

  • Chlorophyll production
  • Source: The soil
• Minerals required by animals

  • Calcium (Ca)
  • Iron (Fe)
• Calcium (Ca) for animals

  • Needed for the formation of teeth and bones
  • Source: Milk, cheese
• Iron (Fe) for animals

  • Formation of haemoglobin (to help transport oxygen)
  • Source: Meat, green vegetables
• Functions of water


  • A component of cytoplasm and body fluids (70-95% of cell mass)
  • A solvent and medium in which chemical reactions take place
• Metabolism


  • Anabolic reactions: Formation of large complex molecules from smaller molecules
  • Catabolism: Breakdown of large molecules into smaller smaller molecules
• Anabolic reactions


  • Requires energy e.g. light
  • e.g. Photosynthesis
• Catabolism


  • Releases energy
  • e.g. Respiration