chapter 3

• Classes of Food


  • Carbohydrate
  • Protein
  • Fat
  • Vitamin
  • Mineral
  • Fibre
  • Water
• Carbohydrate


  Contains carbon, hydrogen and oxygen<|>Supplies a lot of energy
• Carbohydrate


  • Starch - food stored in plants
  • Glycogen - food stored in animals
  • Cellulose - forms the cell wall of plants
• Protein


  Contains carbon, hydrogen, oxygen and nitrogen<|>Required for growth, repair damaged tissues and to replace dead cells<|>Used to synthesise enzymes, hormones and antibodies
• Protein


  • Chicken
  • Meat
  • Seafood
• Fat


  Contains carbon, hydrogen and oxygen<|>Formed from glycerol and fatty acid<|>High energy source and storage<|>Protects organs, transports vitamins, regulates body temperature
• Vitamin


  Needed in small quantities to maintain good health
• Vitamins


  • Water-soluble (Vitamin B and C)
  • Fat-soluble (Vitamin A,D,E and K)
• Vitamin A


  Maintains skin health
• Vitamin B


  Helps with formation of blood cells
• Vitamin C


  Maintains health of gums and mouth
• Vitamin D


  Strengthens tooth enamel
• Vitamin E


  Maintains functions of reproductive system
• Vitamin K


  Speeds up blood-clotting process
• Fibre


  Comprises cellulose found in plant cell walls<|>Stimulates peristalsis to prevent constipation
• Fibre


  • Vegetables
  • Grains
  • High fibre bread
• Mineral


  Does not supply energy but required in small quantities to regulate body processes and maintain health
• Water


  Contains hydrogen and oxygen<|>Acts as chemical solvent, transportation medium, regulates body temperature
• Calcium


  Strengthens bones and teeth<|>Effects of deficiency: Rickets, Osteoporosis
• Sodium


  Maintains functions of nervous system<|>Effects of deficiency: Muscle cramps
• Iron


  Builds haemoglobin in blood<|>Effects of deficiency: Anaemia
• Iodine


  Helps with functions of thyroid gland<|>Effects of deficiency: Goiter
• Phosphorus


  Forms nucleic acid in DNA and RNA<|>Effects of deficiency: Brittle teeth, Cannot build DNA and RNA
• Potassium


  Helps with muscle contraction<|>Effects of deficiency: Paralysis
• Balanced diet


  A diet that contains all the food classes in the right quantities that are required by the body
• Factors that influence calorific requirement

  • Body size
  • Age
  • Work
  • Gender
  • State of health
  • Climate
• Calorific value


  The total amount of energy released when 1 g of food is burned
• 1 calorie (cal) = 4.2 joule (J)
• 1 kilocalorie (kcal) = 4.2 kilojoule (kJ)
• Food digestion


  Process of breaking down complex food into small, soluble molecules that can be absorbed by body cells
• Digestion


  1. Physical: Breaking down food into smaller particles using teeth, tongue, and saliva. Involves peristalsis. Happens in the mouth. Does not involve enzymes.

  2. Chemical: Breaking down complex molecules into simple molecules using enzymes. Happens in the mouth, stomach, duodenum, and intestine. Involves enzymes.
• Human Digestive System


  • Mouth: Food chewed by teeth. Salivary amylase breaks down starch into maltose.
  • Oesophagus: Food called bolus. Peristalsis pushes food into stomach.
  • Stomach: Stomach wall secretes protease and hydrochloric acid. Hydrochloric acid activates protease which breaks down protein into polypeptides. Semi-liquid food called chyme.
  • Duodenum: Liver produces bile which emulsifies fat and neutralises acid in chyme. Pancreas produces pancreatic juice with enzymes amylase, protease, and lipase. Pancreatic amylase digests starch into maltose. Protease digests polypeptides into dipeptides. Lipase digests fat into fatty acids and glycerol.
  • Small Intestine: Maltase digests maltose into glucose. Protease digests dipeptides into amino acids.
  • Large Intestine: Undigested food enters. Water reabsorption happens.
  • Rectum: Undigested food, known as faeces, enters and is stored.
  • Anus: Faeces excreted from the body.
• Villi


  • Millions of fine projections on the wall of the small intestine
  • Increases the surface area for the process of digested food
• Wall of the villus

  • Very thin, one-cell thick
  • Increases the rate of absorption
• Surface of small intestine

  • Has many folds
  • Adds to the surface area
  • Increases the absorption rate of the products of digestion
• Blood vessels in the small intestine


  Function is to transport nutrients to all parts of the body
• Process of Transporting the Products of Digestion

  1. Molecules absorbed into the villus undergo assimilation

  2. Assimilation is the process of distributing the end products of digestion for the use of the cells in our body
• How our body uses the end products of digestion

  • Glucose is used to produce energy
  • Amino acid is used to form component of cells
  • Fatty acid and glycerol combine to form fat which is used as heat insulator and to protect internal organs
• Defecation

  1. Food not absorbed by small intestine moves into large intestine

  2. Water and minerals reabsorbed into bloodstream

  3. Remaining solid waste called faeces

  4. Faeces stored temporarily in rectum

  5. Eliminated through anus