Edexcel GCSE Biology (1BI0) — Health, Disease and Medicines
When someone coughs in a crowded room, invisible clouds of moisture can linger in the air for hours. This is precisely how tuberculosis spreads from person to person. Tuberculosis is caused by a bacterial pathogen called Mycobacterium tuberculosis.
It spreads through airborne transmission via a process known as droplet infection. When an infected individual coughs or sneezes, the bacteria are expelled outward inside tiny droplets of moisture. These droplets remain suspended in the air until an uninfected person breathes them in, carrying the bacteria directly into their lungs.
Once inside the lungs, the bacteria begin to multiply and damage the tissue. This leads to severe symptoms, most notably a persistent chronic cough, fever, and the coughing up of blood-stained mucus.
Stopping a bacterial outbreak requires a multi-layered approach, from individual treatments to global public health strategies. A primary prevention method is the BCG vaccine, which provides active immunity. It contains an attenuated (weakened) strain of a related bacterium, prompting the body's white blood cells to produce specific antibodies and memory cells for a faster, stronger secondary immune response.
Infected individuals must be treated with a long course of antibiotics. These medicines inhibit bacterial processes, such as building cell walls, effectively killing the pathogen. By identifying and treating infected people, we also protect the wider public, as the patient is no longer a source of transmission.
Patients must complete their entire course of antibiotics (often lasting six months or more) to prevent the bacteria from developing antibiotic resistance. Environmentally, transmission can be prevented by improving indoor ventilation to disperse airborne droplets and avoiding overcrowded living conditions.
A gentle summer breeze might seem harmless, but it can carry microscopic threats across entire continents or oceans. is a lethal plant disease spread this way, caused by the fungus . It specifically targets and kills ash trees.
Unlike tuberculosis, which requires moisture droplets, this pathogen spreads via fungal spores. These microscopic spores are highly adapted for wind-borne dispersal and can travel tens of miles on air currents. Once the spores land on healthy ash leaves, they germinate and invade the tree's bark and vascular system.
The infection blocks the tree's ability to transport essential water and nutrients. As a result, the tree suffers from leaf loss, wilting top branches (crown dieback), and dark, diamond-shaped dead patches on the bark known as lesions.
Protecting our woodlands often means focusing on the dead leaves on the forest floor rather than the living trees above. The H. fraxineus fungus survives the winter hiding in fallen leaf litter, specifically on the rachis (the stalk of the leaf).
During the summer, tiny fruiting bodies grow on these dead leaves and release their spores into the wind. Therefore, a highly effective prevention strategy is clearing, burning, or deep-composting all fallen ash leaves during autumn and winter. This breaks the lifecycle by physically destroying the source of the fungal spores.
For trees that are already diseased, felling (cutting down) and removing infected trees is a vital control strategy. This prevents the fungus from continuing to produce spores and spreading to healthy trees nearby. In many cases, infected woodlands are replanted with different tree species that are not susceptible to the fungus.
To prevent the disease from entering new areas, governments enforce strict biosecurity measures. This includes legal bans on importing ash trees or moving ash saplings out of infected zones. Forestry workers must also clean their boots, vehicle tyres, and tools to ensure they do not accidentally transport infected soil or leaf fragments.
Students often confuse the pathogen types. Remember that TB is always caused by a bacterium (not a virus), which is why antibiotics are an effective treatment.
In Edexcel mark schemes, treating a TB patient with antibiotics frequently scores marks as a 'prevention' strategy, because it stops that individual from transmitting the disease to the wider public.
Examiners require you to explicitly state the full chain of transmission for TB: link the action of 'coughing/sneezing' directly to the release of 'airborne droplets', which are then 'inhaled'.
When answering an 'Explain' question on prevention for Chalara ash dieback, always link the action to the mechanism (e.g., state 'clear leaf litter' AND explain 'because it removes the source of the wind-borne fungal spores').
Don't forget that for plants, prevention includes felling (removing) infected trees. This stops them from being a source of spores for the rest of the forest.
Pathogen
A microorganism that causes disease, such as bacteria, fungi, viruses, or protists.
Mycobacterium tuberculosis
The specific bacterial pathogen responsible for causing the disease tuberculosis in humans.
Airborne transmission
The spread of a pathogen through the air, often in small moisture droplets or spores, which are then inhaled by a new host.
Droplet infection
A mechanism of transmission where pathogens are carried in tiny drops of moisture expelled by coughing or sneezing.
Attenuated
A pathogen that has been weakened or treated so it cannot cause disease, but can still trigger a protective immune response.
Specific antibodies
Proteins produced by white blood cells (lymphocytes) that bind to the unique antigens of a particular pathogen to destroy it.
Antibiotics
Medicines used to treat bacterial infections by killing bacteria or inhibiting their growth; they are completely ineffective against viruses.
Antibiotic resistance
When bacteria mutate and are no longer killed by the antibiotics previously used to treat them, often caused by failing to complete a course of medication.
Chalara Ash Dieback
A lethal fungal disease of ash trees characterized by leaf loss, crown dieback, and bark lesions, spread by wind-borne spores.
Hymenoscyphus fraxineus
The specific fungal pathogen that causes Chalara Ash Dieback.
Fungal spores
Microscopic reproductive cells released by fungi, which are adapted for long-distance dispersal by the wind.
Lesion
A necrotic (dead) area of damage on the bark, trunk, or leaf of a plant caused by an infection.
Leaf litter
Fallen leaves and natural debris on the ground where fungi like H. fraxineus can survive over the winter.
Rachis
The central stalk of a compound leaf, which serves as the specific site where the ash dieback fungus produces its spores.
Felling
The act of cutting down and removing infected trees to prevent the further spread of a pathogen.
Biosecurity
Strict physical measures and legal restrictions taken to prevent the introduction or spread of harmful organisms into a new area.
Put your knowledge into practice — try past paper questions for Biology
Pathogen
A microorganism that causes disease, such as bacteria, fungi, viruses, or protists.
Mycobacterium tuberculosis
The specific bacterial pathogen responsible for causing the disease tuberculosis in humans.
Airborne transmission
The spread of a pathogen through the air, often in small moisture droplets or spores, which are then inhaled by a new host.
Droplet infection
A mechanism of transmission where pathogens are carried in tiny drops of moisture expelled by coughing or sneezing.
Attenuated
A pathogen that has been weakened or treated so it cannot cause disease, but can still trigger a protective immune response.
Specific antibodies
Proteins produced by white blood cells (lymphocytes) that bind to the unique antigens of a particular pathogen to destroy it.
Antibiotics
Medicines used to treat bacterial infections by killing bacteria or inhibiting their growth; they are completely ineffective against viruses.
Antibiotic resistance
When bacteria mutate and are no longer killed by the antibiotics previously used to treat them, often caused by failing to complete a course of medication.
Chalara Ash Dieback
A lethal fungal disease of ash trees characterized by leaf loss, crown dieback, and bark lesions, spread by wind-borne spores.
Hymenoscyphus fraxineus
The specific fungal pathogen that causes Chalara Ash Dieback.
Fungal spores
Microscopic reproductive cells released by fungi, which are adapted for long-distance dispersal by the wind.
Lesion
A necrotic (dead) area of damage on the bark, trunk, or leaf of a plant caused by an infection.
Leaf litter
Fallen leaves and natural debris on the ground where fungi like H. fraxineus can survive over the winter.
Rachis
The central stalk of a compound leaf, which serves as the specific site where the ash dieback fungus produces its spores.
Felling
The act of cutting down and removing infected trees to prevent the further spread of a pathogen.
Biosecurity
Strict physical measures and legal restrictions taken to prevent the introduction or spread of harmful organisms into a new area.
