Biology IGCSE - Diseases and Immunity

Pathogen

disease-causing organism

Transmissible disease

A disease that can be passed from one host to another → transmissible diseases are caused by pathogens

Transmission

 movement of a pathogen from one host to another

 Features of viruses

• Protein coat → protects virus

• Genetic material (DNA or RNA) → carries instructions for making new viruses

How pathogen are transmitted

• by direct contact → e.g. through blood + other body fluids

• indirectly → e.g. contaminated surfaces, food, animals + air

Body defences against pathogens → skin (physical barrier)

prevents pathogens from entering body

Body defences against pathogens → hairs in the nose (physical barrier)

Trap dust + microbes → stopps them from entering lungs

Body defences against pathogens → mucus (chemical barrier)

Sticky substance in airways that traps pathogens → moved out by cilia

Body defences against pathogens → stomach acid (chemical barrier)

Kills bacteria + pathogens swallowed in food or mucus

Body defences against pathogens → white blood cells (chemical barrier)

Part of immune system → destroy pathogens by ingesting them (phagocytosis) or producing antibodies

Importance of a clean water supply in controlling the spread of disease

prevents spread of waterborne diseases → e.g. cholera, typhoid → ensures people drink + use safe, uncontaminated water.

Importance of hygienic food preparation in controlling the spread of disease

stops bacteria from entering body through contaminated or undercooked food → prevents food poisoning + other infections

Importance of good personal hygiene in controlling the spread of disease

regular handwashing + cleanliness remove harmful microbes → reduces risk of spreading germs through touch, coughing, or sneezing

Importance of waste disposal in controlling the spread of disease

proper disposal of rubbish + waste prevents growth of bacteria + breeding of pests → e.g. flies, rats → helps avoid contamination of food + water sources

Importance of sewage treatment in controlling the spread of disease

removes harmful microbes + waste from human sewage → prevents pollution of water bodies → reduces risk of disease spreading through water

Active immunity

Defence against a pathogen by antibody production in the body

Host

An organism in which a pathogen lives and reproduces

Antibody

Proteins that bind to antigens leading to direct destruction of pathogens or marking of pathogens for destruction by phagocytes

Antigen

chemical that is recognised by the body as being ‘foreign’ and stimulates an immune response

Immune response

reaction of the body to the presence of an antigen; it involves the production of antibodies

each pathogen has its own antigens → have specific shapes

specific antibodies have complementary shapes → fit specific antigens

How does immune system know what to attack

→ all cells have a specific antigen on their surface (special protein)

→ each human has their own specific shape of antigen on their surface of their cells → these are self antigen

→ pathogen, including viruses, also have their own specific antigen → non - self antigen

→ antibodies are protein produced by lymphocytes that bind specific antigens

Why are antibodies unable to kill viruses

• viruses inject themselves into host body cells

• antibodies don’t affect body cells

• antibodies affect bacteria cell walls → viruses don’t have a cell wall

Why bacteria has become more resistant

• Not finishing a course of antibiotics according to doctor’s instruction

• Taking antibiotics when not needed

• Mass use of antibiotics on farm animals

Vaccine

harmless preparation of dead or inactivated pathogens that is injected into the body to induce an immune response

Explain that active immunity is gained after an infection by a pathogen or by vaccination

• It can happen naturally after an infection

• It can also happen artificially through vaccination → weakened or inactive form of the pathogen is introduced to trigger the immune response

Process of vaccination

1. weakened pathogens or their antigens are put into body

2. antigens stimulate an immune response by lymphocytes → produce antibodies

3. memory cells are produced → give long-term immunity

Vaccinations are available for some pathogens → help control spread of diseases

role of vaccination in controlling spread of diseases

• Stimulating immune system → produce antibodies without causing illness

• Protecting individuals from getting infected

• Reducing no. of infected people → lowers chance of transmission

• Helping create herd immunity → unvaccinated people are protected because disease can’t spread easily