Common Infections Damage Specific Tissues
Communicable disease
A disease that can be passed from one organism to another. It is caused by a pathogen, such as a bacterium, virus, fungus or protist.
- The symptoms of an infection depend on the pathogen, the tissue it infects and the damage it causes.
- You should link each named disease to its pathogen group and its characteristic effect.
Disease descriptions score when the pathogen type and the resulting damage or symptom are both correct.
Bacterial Diseases
Bacterium
A single-celled prokaryotic microorganism. Harmful bacteria cause disease by reproducing rapidly and often releasing toxins that damage cells.
- Cholera is caused by bacteria that release a toxin in the small intestine, causing severe watery diarrhoea and dangerous dehydration.
- Tuberculosis is caused by bacteria that mainly infect the lungs, where inflammation and tissue damage reduce gas exchange.
- Stomach ulcers can be caused by Helicobacter bacteria that damage the stomach lining, allowing acid to injure the tissue beneath.
- Cholera toxin causes ions to move into the intestinal lumen, and water follows by osmosis, producing severe watery diarrhoea and dehydration.
- Tuberculosis bacteria can remain in the lungs, where repeated immune responses damage alveoli and reduce the surface available for gas exchange.
- Helicobacter damages the protective stomach lining, so hydrochloric acid and digestive enzymes reach underlying tissue and form an ulcer.
cholera toxin causes water and ions to move into the intestine, so the patient loses large volumes of watery faeces and becomes dehydrated.
Fungal and Protist Diseases
Vector
A living organism that carries a pathogen from one host to another without catching the disease itself, for example a mosquito carrying the malarial protist.
- Chalara ash dieback is a fungal disease of ash trees that causes leaf loss, bark lesions and dieback of shoots and branches.
- Malaria is caused by a protist carried by female Anopheles mosquitoes, and it damages liver cells and red blood cells.
- Repeated destruction of red blood cells causes cycles of fever and can lead to anaemia.
- Ash dieback spreads through fungal spores, causing dark bark lesions, leaf loss and death of shoots as conducting tissues are damaged.
- The malarial protist first reproduces in liver cells and later in red blood cells, whose repeated rupture produces cycles of fever and anaemia.
The mosquito is the vector for malaria, while the protist is the pathogen.
Viral Diseases
- HIV infects and destroys white blood cells, so the immune system becomes less able to control other pathogens.
- Untreated HIV infection can progress to AIDS, when opportunistic infections and some cancers can become life-threatening.
- Ebola is a viral disease that causes severe fever and can damage blood vessels, leading to internal and external bleeding.
- HIV lowers the number of functioning white blood cells over years, while AIDS describes the severe immune-deficiency stage that may follow.
- Ebola damages several organs and blood vessels, so severe fluid loss and haemorrhage can lead to shock.
- Write disease answers as a linked pair: identify the pathogen group, then state the named tissue damage or symptom.
- For HIV, connect white-blood-cell destruction to weaker immunity rather than saying only that HIV causes AIDS.
Distinguish Disease From Symptom
- Diarrhoea, fever and bleeding are symptoms, while cholera, malaria and Ebola are diseases.
- A symptom alone does not identify the pathogen because different diseases can produce similar symptoms.
- What causes cholera and what symptom does it produce?
- How does tuberculosis damage the body?
- Which pathogen causes ash dieback?
- Explain how HIV can lead to AIDS.
- What tissues are damaged by malaria?
