Interactions With the Environment: Preventing, Treating and Curing Diseases — AQA Combined Science: Synergy
This topic covers communicable diseases, how the body defends itself, vaccination, medicines, drug testing, genetic modification and stem cells.
Spread of communicable diseases
Pathogens (bacteria, viruses, fungi and protists) cause communicable diseases. They spread by direct contact, water and air (droplets), and by vectors. Spread is reduced by hygiene, isolating the infected, destroying vectors and vaccination.
Human communicable diseases (examples)
- Measles (viral) — droplets; fever and rash; MMR vaccine.
- HIV (viral) — bodily fluids; attacks immune cells; antiretroviral drugs.
- Salmonella (bacterial) — contaminated food; food poisoning.
- Gonorrhoea (bacterial, STI) — antibiotics; barrier contraception.
- Malaria (protist) — mosquito vector; nets and preventing breeding.
Defences against pathogens
Non-specific defences: skin (barrier), nose (hairs/mucus), trachea and bronchi (mucus and cilia), stomach acid.
The human immune system
If pathogens enter, white blood cells:
- engulf them (phagocytosis),
- produce antibodies specific to the pathogen's antigens,
- produce antitoxins to neutralise toxins.
Vaccination
A vaccine contains dead or inactive pathogen (or antigens) that triggers white blood cells to make antibodies. If the real pathogen later enters, the body responds quickly and strongly, preventing illness. Widespread vaccination gives herd immunity.
Medicines
- Painkillers treat symptoms only.
- Antibiotics kill bacteria (not viruses). Antibiotic resistance (e.g. MRSA) is rising due to overuse — reduce it by not over-prescribing and finishing courses.
Many drugs originated from plants/microorganisms (digitalis from foxgloves, aspirin from willow, penicillin from mould).
Testing new drugs
New drugs are tested for safety, efficacy, toxicity and dose:
- Preclinical — cells, tissues and animals.
- Clinical trials — healthy volunteers, then patients.
- Double-blind trials with a placebo to remove bias. Results are peer reviewed.
Genetic modification
Genetic engineering transfers a gene from one organism to another to give a desired feature (e.g. bacteria making human insulin, herbicide-resistant crops). Benefits include higher yields and medicines; concerns include effects on wild populations and ethics.
Stem cells
Stem cells can be used to replace damaged cells (e.g. treating diabetes or paralysis). Therapeutic cloning produces stem cells genetically identical to the patient, avoiding rejection. There are risks (infection) and ethical issues around using embryos.
Interactions between diseases
Diseases can interact: a weak immune system increases susceptibility to communicable disease; some viruses trigger cancers; some pathogens trigger allergies; physical illness can lead to mental illness.
Exam tips
- Learn named diseases with type, spread and prevention.
- Vaccines work before infection; antibiotics treat bacterial infection.
- Explain antibiotic resistance using natural selection.
- Know why placebos and double-blind trials remove bias.