AS Biology: Unit 1 - Section 1

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  • Created by: Zoe Key
  • Created on: 03-04-12 09:00


Pathogens - any organism that causes diseases e.g. can be microorganisms such as bacteria or larger organisms such as tapeworms.

Pathogens will enter another organism (the host cell) through any interface with the environment. For humans the main three environmental interfaces are: the skin, the digestive system and the respiratory system. Each of these systems has preventative measures agains pathogens: skin itself, stomach acid and the mucus lining and cilla in the throat.

Pathogens cause disease by producing toxins and damaging cells. The production of toxins interrupts the fuction of something in the body, causing problems and irregularities. Cell damage can be done in three ways: rupturing the cells so the nutrients within are released, using up the nutrients from inside the cell, eventually killing it and replicating inside of cells so they burst.

Lifestyle is a major factor effecting the likelihood of contracting a disease for example poor diet can increase the chances of contracting coronary heart disease and smoking will increase your chances of getting cancer AND coronary heart disease. Even a late change of lifestyle will reduce these chances.

The Immune System:

Antigens - molecules (usually proteins or polysaccharides) that are found on the surface of cells.

 If an antigen is recognised as foreign by phagocytes or lymphocytes (white blood cells) the immune system is activated. The immune system has four main steps.

  • 1. Phagocytes engulf pathogens - When a phagocyte (a type of white blood cell) recognises a pathogen's antigens as foreign it engulf the pathogen in it's cytoplasm. The pathogen is now in a phagocytic vacuole. A lysosome joins with the edge of the vacuole and releases lysosomal enzymes into it. These enzymes digest the pathogen and the phagocyte then presents the pathogen's anttigens on it's surface to activate other immune cells.
  • 2. Phagocytes activate T-Cells - T-Cells are also a form of white blood cells (produced in the bone marrow and matured in the thymus gland). These cells can bind to the antigens on phagocytes which activates the T-Cells. The T-Cells then do one of two things:they either release substances which activate the B-Cells or kill the phagocyte.
  • 3. B-Cells are activated - Once the B-Cells have been activated they find pathogens which are presenting antigens which the antibodies on the surface of the B-Cells can bind to. This also activates B-Cells, along with the substance released from the T-Cells. The then activated B-Cells divide to form plasma cells.
  • 4. Plasma cells make


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