3.1.6 Human Defence Systems

• What is an antigen?

  Any substance that your body sees as foreign, which then causes your immune system to produce antibodies against it.
• What are examples of an antigen?

  The toxins and cell walls of pathogens.
• What is an antibody?

  A protein produced by our white blood cells that binds to specific antigens which acts as a signal to our immune system to destroy the antigen (or the pathogen it is part of).
• What are some examples of barriers that reduce the entry of pathogens?

  Skin, enzymes in tears, nose hairs, eyelashes, cilia, etc.
• How does skin help to defend against disease?

  It secretes oils and antimicrobial substances that kill pathogens and covers the body, physically preventing pathogens from entering.
• Does skin act as a physical or chemical barrier to pathogens?

  Physical.
• The nose has hairs inside it that act as a physical barrier to pathogens. What are the hairs in the nose coated with to catch pathogens?


  Mucus.
• The cells that line the trachea, bronchi and bronchioles have tiny hair-like projections that waft the mucus and pathogens away from the lungs. What are these structures called?


  Cilia.
• What substance does the stomach produce to kill pathogens?

  Hydrochloric acid.
• Does the acid produced by the stomach act as a physical barrier, or a chemical barrier, to pathogens?

  Chemical.
• What is the role of the immune system?

  To locate and destroy pathogens that enter the body.
• Which type of cells are part of the immune system?

  White blood cells.
• What are some functions of white blood cells?

  Phagocytosis and producing both antitoxins and antibodies.
• What type of white blood cell is phagocytosis carried out by?

  A phagocyte.
• What are the three stages of phagocytosis?

  1. The first step is for the phagocyte to track down a pathogen, and then bind to it.
  2. The phagocyte's membrane will then surround the pathogen and engulf it.
  3. Finally, enzymes inside the phagocyte break down the pathogen in order to destroy it.
• What do antitoxins do?

  Bind to and neutralise the toxins produced by bacteria.
• What are the white blood cells that produce antibodies called?

  B-lymphocytes.
• What is the most important part of the immune system?

  White blood cells.
• How do eyelashes defend against pathogens?

  Eyelashes act as a physical barrier to prevent pathogens from entering the eyes. They also catch any dirt.
• How do you remove mucus from the body?

  Swallowing/blowing your nose.
• How is a scab formed?

  By blood clotting and platelets sticking together.
• What do the trachea and bronchi secrete to trap pathogens?

  Mucus.