IB Biology topic 6.3

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6.3.1 Define pathogen
an organisms or virus that causes a disease.
6.3.2 Explain why antibiotics are effective against bacteria but not against viruses.
Antibiotics - chemicals produced by microorganisms to kill or control the growth of other microorganisms. This is achieved by blocking processes in bacterial cells which does not cause any harm to human cells. Viruses, however, carry out very few processes themselves, they instead rely on the host cell. It is therefore not possible to block these processes without harming the human cells and therefore virus diseases cannot be treated with antibiotics.
6.3.3 Outline the role of skin and mucous membranes in defence against pathogens.
Roles of skin:
1) outer layer of skin is tough - physical barrier.
2) glands in skin secretes lactic acid and fatty acids = resulting in the skin being acidic; this prevents the growth of most pathogenic bacteria.
Roles of mucous (found in nose, trachea, vagina and urethra)
1) contain lysozyme - an enzyme that can kill many bacteria.
2) pathogens entering the trachea stick to the mucous and cilia then push the mucous and bacteria out of the trachea - coughing.
6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues.
Leucocytes are white blood cells. Some leucocytes are phagocytes. These cells can identify pathogens and ingest them by endocytosis and kill and digest them inside the cell with enzymes from lysosomes.
6.3.5 Distinguish between antigens and antibodies.
Antigens - are foreign substances that stimulate the production of antibodies; they can be cells walls of pathogenic bacteria or fungi and protein coats of pathogenic viruses.
Antibodies - are proteins that recognise and bind to specific antigens. In this way they defend the body against pathogens by stimulating their destruction.
6.3.6 Explain antibody production.
(1) antibodies are made by lymphocytes, one of the two main types of leucocytes.
(2) One lymphocyte = one antibody; some of each antibody is placed in the plasma membrane of its lymphocyte with the antigen-binding site projecting.
(3) a pathogen enters the body and bind to the antibodies in the plasma membrane of one type of lymphocytes.
(4) when an antigen binds to an antibody the lymphocyte becomes active and divide by mitosis to produce a clone of many identical cells.
(5) the clone of identical cells produce large quantities of the same antibody - the one needed to fight this specific pathogen.
6.3.7 Outline the effects of HIV on the immune system.
HIV causes AIDS. The virus infects a type of lymphocyte that plays a vital role in antibody production. Over a period of years the lymphocytes will be destroyed and antibodies cannot be produced. This destroys the immune system causing the body to be very vulnerable to pathogens that normally would be controlled easily.
6.3.8 Discuss the cause, transmission and social implications of AIDS
Caused by HIV a virus that destroys the immune system.
Transmission
- in traces of blood on a hypodermic needle shared by drug users.
- across the placenta from mother to baby or through cuts during childbirth or in milk during breast-feeding.
- in transfusions of blood
Social implications
- families and friends suffer grief
- family becomes poorer if the person with AIDS was the wage earner and is refused life insurance
- individuals with AIDS become stigmatised and cannot find partners, housing or employment
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