AQA GCSE Biology

Revision Notes

2.2.1 The Human Digestive System

Digestion: Basics

  • The digestive system is an example of an organ system in which several organs work together to digest and absorb food
  • Digestion is a process in which relatively large, insoluble molecules in food (such as starch, proteins) are broken down into smaller, soluble molecules that can be absorbed into the bloodstream and delivered to cells in the body
  • These small soluble molecules (such as glucose and amino acids) are used either to provide cells with energy (via respiration), or with materials with which they can build other molecules to grow, repair and function

Tissues & Organs of the Human Digestive System

  • The human digestive system is made up of the organs that form the alimentary canal and accessory organs
    • The alimentary canal is the passage through which food passes through the body from the mouth to the anus. Digestion occurs here
    • Accessory organs produce substances that are needed for digestion to occur (such as enzymes and bile) but food does not pass directly through these organs

The human digestive system, IGCSE & GCSE Biology revision notes

The human digestive system includes the organs that form the alimentary canal, and accessory organs that aid the process of digestion

Alimentary canal and accessory structures table

The Alimentary Canal table, IGCSE & GCSE Biology revision notes

The Importance of Bacteria in Digestion

  • The large intestine is home to hundreds of species of bacteria
  • These bacteria form a microbial ecosystem (the microbiota, or gut flora) that play an essential role in human digestion of food by:
    • Breaking down substances we can’t digest (like cellulose)
    • Supplying essential nutrients
    • Synthesising vitamin K
    • Providing competition with any harmful bacteria to restrict their growth
  • Taking antibiotics can disrupt the gut microbiota which can cause short-term problems with digestion

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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