Edexcel GCSE Biology (1BI0) — Health, Disease and Medicines
An infected person can lose up to 20 to 30 litres of fluid in a single day. This extreme dehydration is caused by the pathogen known as Vibrio cholerae, a bacterium that targets the small intestine.
Cholera is primarily spread through the faecal-oral route. Because the bacteria are carried in human waste, Vibrio cholerae acts as a waterborne pathogen. Transmission occurs when people ingest contaminated water or food that has been mixed with untreated faeces from an infected individual.
Normally, your gut absorbs water, but during a cholera infection, this process goes violently into reverse. Once the bacteria colonise the lining of the small intestine, they secrete a harmful toxin.
This toxin forces the cells of the intestinal lining to pump chloride ions () out into the lumen (the empty middle space) of the gut.
Osmotic Gradient Example:
The accumulation of chloride ions lowers the water potential in the gut lumen. Consequently, water rapidly moves out of the blood and intestinal cells into the gut by osmosis. This massive shift of water causes profuse watery diarrhoea (often called "rice-water stool") and life-threatening dehydration, which is treated using Oral Rehydration Therapy (ORT).
How do we stop a microscopic killer that hides in our drinking water? Breaking the transmission cycle requires targeting the contaminated sources and maintaining strict sanitation.
Stomach ulcers are painful sores in the stomach lining caused by the pathogen Helicobacter pylori. This spiral-shaped bacterium is highly adapted to survive in the acidic environment of the stomach.
This bacterium is primarily spread through oral transmission. People contract the infection by ingesting contaminated food or water, or through direct oral-to-oral contact, such as sharing saliva. Infections often start in childhood but can remain completely without symptoms for many years.
The stomach contains strong hydrochloric acid, so how does a bacterium survive there? H. pylori secretes an enzyme called urease, which neutralises the highly acidic environment immediately surrounding the cell.
This chemical shield allows the bacteria to safely burrow into the stomach's protective mucus layer. As the bacteria multiply, they do not directly eat the stomach wall; instead, they irritate and degrade the protective mucus. This damage leaves the delicate stomach epithelium exposed to the highly acidic gastric juices, which burn the tissue and form an ulcer.
Because this pathogen relies on the oral route, simple everyday actions are our best defense against transmission.
A new water treatment plant is built in a town. The number of recorded H. pylori infections drops from 850 cases per year to 170 cases per year. Calculate the percentage decrease in infections.
Step 1: Calculate the change in value.
Step 2: Divide the change by the original value.
Step 3: Multiply by 100 to find the percentage.
Students often state that Helicobacter pylori directly eats the stomach wall. Actually, it only damages the protective mucus lining, which allows the stomach's own acid to burn the wall and create the ulcer.
When asked to 'explain' how cholera causes diarrhoea, examiners look for a step-by-step sequence: mention the toxin, the secretion of chloride ions, the lowering of water potential, and finally, water movement out of cells by osmosis.
Always differentiate between the pathogen (H. pylori) and the disease (stomach ulcers). Don't write 'stomach ulcers are transmitted via water' — write 'the bacterium that causes stomach ulcers is transmitted via water.'
For prevention mark scheme points, always use standard Edexcel phrasing like 'improved hygiene' or 'access to clean water', and specifically state that boiling or chlorinating water 'kills the bacteria'.
Pathogen
A microorganism, such as a bacterium or virus, that causes disease in its host.
Vibrio cholerae
The bacterium responsible for causing the disease cholera.
Faecal-oral route
A transmission pathway where pathogens in faeces pass to the mouth of a new host, usually via contaminated food or water.
Waterborne pathogen
A disease-causing microorganism that is spread through contaminated water.
Contaminated water
Water that contains harmful pathogens or chemicals, making it unsafe to drink.
Toxin
A poisonous substance produced by a living organism, such as a bacterium, that damages host cells.
Chloride ions
Negatively charged particles secreted into the gut during a cholera infection, which alter the water potential.
Osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
Oral Rehydration Therapy (ORT)
A medical treatment consisting of a solution of water, salts, and glucose used to restore fluid balance in dehydrated patients.
Sewage systems
Infrastructure designed to safely remove and treat human waste, preventing it from contaminating drinking water.
Stomach ulcers
Painful sores or breaks in the lining of the stomach, often caused by bacterial infection.
Helicobacter pylori
A spiral-shaped bacterium that infects the stomach lining and causes ulcers.
Oral transmission
The spread of a pathogen from mouth to mouth, or via the ingestion of contaminated food and water.
Urease
An enzyme produced by H. pylori that neutralises stomach acid, allowing the bacteria to survive.
Put your knowledge into practice — try past paper questions for Biology
Pathogen
A microorganism, such as a bacterium or virus, that causes disease in its host.
Vibrio cholerae
The bacterium responsible for causing the disease cholera.
Faecal-oral route
A transmission pathway where pathogens in faeces pass to the mouth of a new host, usually via contaminated food or water.
Waterborne pathogen
A disease-causing microorganism that is spread through contaminated water.
Contaminated water
Water that contains harmful pathogens or chemicals, making it unsafe to drink.
Toxin
A poisonous substance produced by a living organism, such as a bacterium, that damages host cells.
Chloride ions
Negatively charged particles secreted into the gut during a cholera infection, which alter the water potential.
Osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.
Oral Rehydration Therapy (ORT)
A medical treatment consisting of a solution of water, salts, and glucose used to restore fluid balance in dehydrated patients.
Sewage systems
Infrastructure designed to safely remove and treat human waste, preventing it from contaminating drinking water.
Stomach ulcers
Painful sores or breaks in the lining of the stomach, often caused by bacterial infection.
Helicobacter pylori
A spiral-shaped bacterium that infects the stomach lining and causes ulcers.
Oral transmission
The spread of a pathogen from mouth to mouth, or via the ingestion of contaminated food and water.
Urease
An enzyme produced by H. pylori that neutralises stomach acid, allowing the bacteria to survive.
