Biology SL chapter 6.3 (Defence against infectious diseases)

Define a pathogen
A pathogen is a disease-causing micro-organism, virus or prion
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Explain why antibiotics work against bacteria but not viruses
Antibiotics work by inhibiting metabolic pathways of prokaryotes. Specific prokaryotic features such as key enzymes or 70S ribosomes can also be targeted. Viruses do not have metabolic pathways which can be blocked.
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First line of defence against infectious diseases
These are surface barriers which prevent the entry of pathogenic substances. These are the skin and mucus membranes
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Role of skin in defence against infectious diseases
Protects external structures, dry, thick and tough made of mostly dead cells. Contains glands which inhibit growth of bacteria in addition to releasing acidic secretions which stop the bacteria from growing
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Role of mucus membranes in defence against infectious diseases
Protects internal structures which are accessible from the outside (******, nostrils, ears). Thin, living surface that releases fluids to wash away pathogens, mucus membranes have small hairs to carry away pathogens
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Second line of defense against infectious diseases
This line of defense involves the non-specific defense mechanisms. These mechanisms do not differentiate between microorganisms and always invoke the same response. These mechanisms include phagocytic leucocytes, inflammation and fever
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Actions of phagocytic leucocytes pt1
These leucocytes circulate in the blood but may move into body tissue in response to infection.They concentrate at these sites due to release of histamine from damaged cells. Pathogens are engulfed by pseudopodia, sequestering it in a vesicle
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Actions of phagocytic leucocytes pt2
The vesicle may then fuse with the lysosome to digest the pathogen.Some of the pathogens antigenic fragments may be presented on the surface of the macrophage, in order to help stimulate antibody production
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Third line of defence
The third line of defence are the specific defences, coordinated by a type of leucocyte called lymphocytes. These can recognise and respond specifically to different types of micro-organism and have memory
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Distinguish between antigens and antibodes
Antigen: A substance that the body recognises as foreign and that can evoke an immune response. Antibody: A protein produced by certain white blood cells (B lymphocytes, plasma cells) in response to an antigen
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Explain antibody production pt1
B lymphocytes are antibody-producing cells that develop in bone marrow to produce highly specific antibody that recognises one type of antigen, When wandering macrophages encounter a pathogen, they digest it
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Explain antibody production pt2
After the parthogen is digested, the macrophages present antigenic fragments to TH cells which activate a B cell which produce massive amounts of antibodies. The B cells will multiply for faster production and some stay behind for long term immunity
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Effect of HIV on immune system
HIV infects the TH cells. Through reverse transcriptase, viral DNA is produced from RNA found in TH cells. After a few year of inactivity, the virus becomes active and destroys the TH cell. This lowers immunity as anti-body production is compromised
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Causes and transmission of AIDS
Cause: Caused by the destruction of the immune system by HIV, AIDS is in the later stages when observable symptoms develop. Transmission: through exchange of body fluids (breast feeding, unprotected sex).
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Social implications of AIDS
People may be stigmatised and discriminated against, majority of people who die of AIDS are at a productive age, affecting workforce. Can result in increased number of orphans
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Card 2

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Explain why antibiotics work against bacteria but not viruses

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Antibiotics work by inhibiting metabolic pathways of prokaryotes. Specific prokaryotic features such as key enzymes or 70S ribosomes can also be targeted. Viruses do not have metabolic pathways which can be blocked.

Card 3

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First line of defence against infectious diseases

Back

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Card 4

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Role of skin in defence against infectious diseases

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Card 5

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Role of mucus membranes in defence against infectious diseases

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