BIOLOGY · Stage 7 · Chapter 3: Microorganisms and Decomposers
Biology 3.4 Using science to prevent disease — Hygiene, Antibiotics and Vaccines
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Lesson summary
3.4 Using science to prevent disease — Hygiene, Antibiotics and Vaccines — Alhussan International Academy — Biology (Stages 7–9) notes: Explain how infections spread and how hygiene, antibiotics and vaccination prevent or treat infectious disease.Droplet infection — breathing, ta…
- Direct contact
- Contaminated food and drink
- Break in the skin
- Scientific advice
- Evidence for masks
- Evidence for social distancing
Section 1 of 7How microorganisms spread
1Droplet infection4 points
- breathing, talking, coughing or sneezing forces tiny droplets containing microorganisms out of the mouth and nose.
- Other people breathe in the droplets.
- A sneeze sends droplets out at about 160 km/h.
- Examples are influenza and TB.
2Direct contact2 points
- spread by the skin of an infected person or by objects covered in microorganisms.
- Examples are verrucas, or microorganisms getting in through the mouth.
3Contaminated food and drink2 points
- water contaminated by human waste, or raw or under-cooked food, takes microorganisms straight into the body.
- Examples are diarrhoea and cholera.
4Break in the skin2 points
- cuts, animal scratches and needle punctures let microorganisms straight into the blood.
- An example is tetanus.
Section 2 of 7Applying science to COVID-19
- COVID-19
- a new disease caused by a virus that spreads by droplet infection and by direct contact.
- Scientific advice
- Wash hands often with soap and use antiseptic hand gel.
- Wear a face mask over the mouth and nose.
- Meet as few people as possible, avoid crowded places and keep a distance, meeting outdoors if possible.
- Cough or sneeze into a tissue or the elbow.
- Stay at home, away from other people, when ill.
- Evidence for masks
- graphs showed that countries with mask-wearing policies had fewer deaths from COVID-19.
- Evidence for social distancing
- in February 2020 infections rose in the Italian towns of Bergamo and Lodi.
- Lodi closed schools and businesses and made people stay at home within 3 days of the first infection.
- Bergamo did the same only after 16 days, and had many more infections.
- Science in society
- scientific understanding is applied across societies to solve real-life problems such as disease control.
Section 3 of 7Hygiene
- Hand washing
- washing with soap before eating and after using the toilet removes bacteria and viruses.
- Clean water and sewage treatment
- they prevent diseases such as cholera.
- Food
- cook it thoroughly and store it in a fridge, because low temperature slows bacterial growth.
- Surgery
- surgeons sterilise instruments and wear gloves to prevent infection during operations.
- Semmelweis
- in the 1840s he showed that doctors washing their hands greatly reduced deaths of mothers after childbirth, before germs were understood.
Section 4 of 7Antibiotics
- Antibiotics = medicines that kill bacteria or stop them from growing, without harming human cells.
- Penicillin
- the first antibiotic, discovered by Alexander Fleming in 1928 from the mould Penicillium.
- Uses
- they treat bacterial infections such as tuberculosis and some throat infections.
- Not for viruses
- viruses lack the cell structures antibiotics attack and live inside our own cells.
Section 5 of 7Antibiotic resistance
- In a population of bacteria, a few carry a random change that makes them resistant.
- When an antibiotic is used, the non-resistant bacteria are killed.
- The resistant bacteria survive and reproduce.
- The population becomes resistant, which is natural selection.
- Causes
- using antibiotics when they are not needed, or not finishing the course, helps resistant strains spread.
- Problem
- resistant bacteria such as MRSA are very hard to treat, so doctors prescribe antibiotics only when necessary.
Section 6 of 7Vaccination
- A vaccine contains a weakened, dead or harmless part of a pathogen, which cannot cause the disease but carries antigens.
- The vaccine is injected.
- White blood cells detect the antigens and make specific antibodies.
- Some of these cells stay in the blood as memory cells.
- If the real pathogen later infects the body, memory cells recognise it and make antibodies very quickly, so the person does not become ill.
- Immunity
- this protection is called immunity.
- History
- Edward Jenner developed the first vaccine, against smallpox, in 1796.
- Vaccination has eradicated smallpox and almost removed polio.
- Side effects
- a few people have side effects, but these are usually mild and much less harmful than the diseases prevented.
Section 7 of 7Herd immunity and comparing methods
- Herd immunity = protection of a population when most people are vaccinated, so the pathogen finds it hard to spread.
- It protects people who cannot be vaccinated, such as babies and people with weak immune systems.
| Method | How it works | Limitation |
|---|---|---|
| Hygiene | Stops pathogens spreading | Needs constant habits and clean water |
| Antibiotics | Kill bacteria after infection | Useless against viruses; resistance |
| Vaccines | Make the body ready before infection | A new vaccine is needed for changing viruses such as influenza |
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