Revision Notes

7.3 Mechanical Digestion

Types of Teeth

  • Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules
  • It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum


  • Teeth are held firmly in the bone of the jaw
  • They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly
  • The differing shapes and sizes of teeth enable them to perform slightly different functions:
    • Incisors – chisel-shaped for biting and cutting
    • Canines – pointed for tearing, holding and biting
    • Premolars and molars – larger, flat surfaces with ridges at the edges for chewing and grinding up food


Types of teeth, IGCSE & GCSE Biology revision notesTypes of teeth

Structure of a Typical Tooth

Structure of a typical tooth, IGCSE & GCSE Biology revision notesStructure of a typical tooth

Dental Decay

  • Tooth decay and gum disease are both caused by bacteria
  • Many bacteria live in the mouth and most are harmless, however some form a sticky film with saliva, called plaque, which coats teeth and the areas where they attach to gums
  • To begin with, plaque is soft and easy to remove, however if it hardens and forms tartar, it cannot be removed by brushing
  • Tartar around the edges of teeth and gums can allow bacteria to work their way into roots, causing gum disease and loss of teeth
  • If sugar is left in the mouth after eating, bacteria in plaque will feed on it
  • They use it in respiration and turn it into acids
  • The acids gradually dissolve the enamel coating of the teeth, working its way into the dentine
  • Dentine is softer than enamel and so dissolves more easily and quickly
  • This is tooth decay and if not dealt with, can cause painful infections and loss of teeth

Dental Health

  • Reducing the amount of sugar eaten can prevent tooth decay
  • Brushing teeth regularly removes the buildup of plaque that can cause gum disease and removes the sugars in the mouth so bacteria cannot turn them into acids and cause tooth decay
  • Teeth should be brushed with a fluoride toothpaste as this helps to strengthen enamel and reduce damage from acids
  • Regular visits to a dentist ensures that any signs of gum disease or tooth decay can be dealt with promptly

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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