Disease Defences

Question 1

Explain how the skin and mucous membranes prevent entry of pathogens into the body.

5 marks

Answer 1

skin: 3 max
- lower pH/** acid **to keep bacteria from growing/ chemical barrier
- fatty acids/ waxes antimicrobial
- physical barrier to prevent entry/ **dry skin **inhibits bacterial growths
- bacteria on skin/ **mucous membranes **prevent other bacteria from growing
- antimicrobial/ lysozyme in sweat and saliva (mucous membrane) to keep bacterial growth in check

mucous membranes: 3 max
- mucous traps bacteria/ sticky/ mucous slightly acidic e.g. vagina
-** cilia **sweep mucous up to be swallowed to kill bacteria
- contain macrophages/ phagocytes

Question 2

Explain the production of antibodies against a pathogen.

8 marks

Answer 2

• antigen/pathogen engulfed by macrophage (by endocytosis)
• presentation of antigen by macrophage on membrane/MHC protein
• **helper T-cell **binds to macrophage
• helper T-cell activated
• activated helper T-cell binds to (inactive) B-cell (releases cytokines)
• B-cell is activated by helper T-cell
• B-cells start to divide/clone
• plasma cells formed/grow
• plasma cell increase numbers of rough ER/Golgi apparatus
• B cells/ clone /** plasma cells begin to produce antibodies** to the specific antigen
• antibodies secreted/ pass out through membrane (by exocytosis)
• memory cells give long-term immunity/ allow rapid antibody production

Question 3

Explain why antibotics are used to treat bacterial but not viral diseases.

2 marks

Answer 3

• Antibiotics are compounds that kill or inhibit the growth of microbes (specifically bacteria) by targeting prokaryotic metabolism
• antibiotics block metabolic pathways in bacteria / inhibit cell wall formation / protein synthesis
  -** viruses use host cell metabolic pathways** / do not possess a cell wall and so are not affected by antibiotics
• antibiotics are not used to treat viral diseases because they are** ineffective and may harm helpful bacteria**

Question 4

Explain the cause, transmission and social implication of AIDS

8 marks

Answer 4

cause:
- acquired immunodeficiency syndrome
- caused by HIV/ human immunodeficiency virus
retrovirus/ RNA to DNA
- enters (and lowers number of) T-helper cells
less antibodies produced/** immune system disabled**/ weakened
- body vulnerable to pathogens (opportunistic infections)

transmission
transmission through body fluids/ does not live long outside the body
through sexual intercourse
sharing of infected needles
mother to fetus/ across placenta
blood transfusions
blood products/ factor VIII used to treat hemophiliacs

social implications
families and friends suffer grief
great costs/ reduction in workforce/ economic implications
discrimination/social stigma
increase in number of orphans/ family structure/ stability affected
reduces promiscuity/ encourages use of condoms

Question 5

Tuberculosis is a disease of the ventilation system. Explain how white blood cells attack the pathogens that cause this disease.

8 marks

Answer 5

B-cells/ lymphocytes produce antibodies
antigen recognized
antigen can be protein in cell wall of pathogen
macrophage presentation of antigen
clone formed/ division of cells
T-helper cells assist
formation of antigen-antibody complex (neutralization/agglutination/precipitation)
phagocytes engulf
engest by endocytosis
pathogen kills
digested by lysosomes
formation of memory cells