2.7 Immuse System & Defences

Question 1

What are the 4 categories that make up the human defence system?

Answer 1

• Physical
• Chemical
• Microbial
• Immune system

Question 2

What are the physical barriers humans contain in their defence system? (4)

Answer 2

• The whole respiratory tract (nasal passage, trachea and lungs) is line with mucus and cilia (hair-like structure) - the mucus traps particles that could contain pathogens and the cilia waft the mucus up to the back of the throat where it can be swallowed
• The skin: acts as a physical barrier, secretes oils and anti microbial substances which can kill the pathogens that rest on it
• Noses: have lots of little hairs and mucus which can trap the pathogens as they flow through the air
• Platelets in the blood clump together to ‘plug’ the wound. This is known as blood clotting. Blood clots stop you losing too much blood and help prevent microorganisms from entering the blood

Question 3

What are the chemical barriers humans contain in their defence system? (3)

Answer 3

• Eyes produce an enzyme called lysozyme in tears, which breaks down bacteria on the surface of the eye
• Saliva contains molecules which kill pathogens that enter the mouth, so they don’t reach the stomach
• Hydrochloric acid in the stomach brings the pH down to 2. This is so acidic that it kills pretty much all of the pathogens

Question 4

White blood cells are constantly roaming your body, patrolling for pathogens. What are its 3 functions?

Answer 4

1. Phagocytosis
2. Producing antibodies
3. Producing antitoxins

Question 5

One way that white blood cells get rid of pathogens is by consuming them. Describe how they do this (4)

Answer 5

• Phagocytosis is carried out by a special type of white blood cell called a phagocyte
• The first step is for the phagocyte to track down a pathogen, and then bind to it
• The phagocyte’s membrane will then surround the pathogen and engulf it
• Finally, enzymes inside the phagocyte break down the pathogen in order to destroy it

Question 6

One way that white blood cell are able to get rid of pathogens is by producing antibodies. Describe how they do this (5)

Answer 6

• Producing antibodies: when white blood cells come across a foreign antigen on a pathogen, receptors in the membrane bind to the antigen. The white blood cells then start to produce proteins called antibodies which lock onto the antigens on the invading cells. The antibodies produced are specific to that type of antigen.
• The white blood cells that detect the pathogen then divide to produce more copies (clones) of the same white blood cell, so that more antibodies can be produced
• Antibodies are produced rapidly and are carried around the body to lock on to all similar pathogens
• The antibodies may disable the pathogen or ‘tag’ the pathogens, which helps the phagocytes find them and engulf them
• Some white blood cells stay around in the blood after the pathogen has been fought off - these are called memory cells. If the person is infected with the same pathogen again, the memory cells will trigger the rapid production of the antibodies needed to destroy it, before the pathogen causes the disease - the person is naturally immune to that pathogen and wont get ill

Question 7

One way that white blood cells are able to get rid of pathogens is by producing antitoxins. Describe how they do this

Answer 7

• Producing antitoxins: some pathogens can cause problems for the body by the toxins which they produce. Some white blood cells also produce antitoxins which are small molecules that bind to these toxins and counteract them. This limits any damage that is done by the invading pathogens

Question 8

What is the difference between antigens and antibodies (2)

Answer 8

• An antigen is any substance that your body sees as foreign, which then causes your immune system to produce antibodies against it. For example, toxins and cell walls of pathogens would be considered antigens
• An antibody on the other hand is a protein produced by our white blood cells that binds to specific antigens. This acts as a signal to our immune system to destroy the antigen (or the pathogen it is part of)