Edexcel GCSE Biology (1BI0) — Health, Disease and Medicines
Walking through a British woodland, you might notice ash trees with stark, bare branches in the middle of summer. This is often due to a highly contagious communicable disease called Chalara ash dieback. It is caused by a fungus (specifically Hymenoscyphus fraxineus) and is usually fatal, with estimates suggesting up to 95% of UK ash trees could eventually die from the infection.
The infection produces two main symptoms required for your exams. First, trees suffer from leaf loss, where leaves develop dark patches, wilt, and drop off prematurely. Second, bark lesions appear as dark, sunken, diamond-shaped wounds on the trunk and branches. These cankers girdle the tree, cutting off the transport of vital water and nutrients and leading to the progressive death of the upper tree (crown dieback).
The fungus spreads primarily through airborne spores carried by the wind over long distances. Because spores drift through the air, infected trees are often found randomly distributed across a forest. Human movement of infected ash trees and seeds through trade also spreads the disease rapidly.
To control the spread, infected trees are removed and burned to eradicate spore production. Governments also use quarantine measures to restrict the import of ash trees and encourage planting different, non-susceptible tree species to diversify woodlands.
The deadliest animal on Earth is not a shark or a tiger, but a tiny flying insect that does not even suffer from the disease it carries. This insect spreads malaria, a disease caused by a protist (a type of single-celled eukaryotic organism) from the Plasmodium genus. The female Anopheles mosquito acts as the vector, transporting the pathogen between human hosts.
The mechanism of infection follows a specific, step-by-step pathway through the human host's body:
The synchronized bursting of red blood cells triggers recurrent (repeated) episodes of fever, chills, and sweating. The widespread destruction of these blood cells also leads to anaemia, severely reducing the body's capacity to transport oxygen.
Controlling the vector is highly effective in preventing transmission. Draining areas of standing water removes the breeding grounds where mosquitoes lay eggs, directly reducing their population. Other prevention strategies include physical barriers like mosquito nets, chemical insect repellents applied to the skin, and insecticides used to kill adults and larvae.
Students often state that the mosquito is the pathogen that causes malaria, but the mosquito is actually the vector; the protist (Plasmodium) is the true pathogen.
When describing the symptoms of Chalara ash dieback, examiners specifically look for the exact phrases 'leaf loss' and 'bark lesions' to award marks.
In questions asking you to describe malaria's damage to the body, you must use the specific words 'burst' or 'rupture' to explain what happens to the liver cells and red blood cells.
Always describe the fever associated with malaria as 'recurrent' or 'repeated,' as this links directly to the life cycle of red blood cells bursting.
If an exam question mentions a 'random distribution' of diseased trees in a woodland, this suggests an airborne pathogen (like Chalara ash dieback) rather than a soil-borne disease.
Communicable disease
A disease that can be spread from one person or organism to another.
Chalara ash dieback
A communicable fungal disease affecting ash trees, characterized by leaf loss and bark damage.
Fungus
A group of organisms that can act as pathogens, including the species responsible for Chalara ash dieback.
Leaf loss
The premature dropping of leaves, often after they develop dark spots or wilt, which is a key symptom of Chalara ash dieback.
Bark lesion
A localized area of diseased or damaged tissue on a tree's bark, often appearing as a sunken or discoloured patch.
Protist
A eukaryotic organism (usually unicellular) that is the pathogen causing malaria.
Vector
An organism that carries a pathogen from one host to another without being infected by the disease itself.
Anaemia
A condition caused by a deficiency of red blood cells, resulting in tiredness due to a reduced capacity to transport oxygen.
Put your knowledge into practice — try past paper questions for Biology
Communicable disease
A disease that can be spread from one person or organism to another.
Chalara ash dieback
A communicable fungal disease affecting ash trees, characterized by leaf loss and bark damage.
Fungus
A group of organisms that can act as pathogens, including the species responsible for Chalara ash dieback.
Leaf loss
The premature dropping of leaves, often after they develop dark spots or wilt, which is a key symptom of Chalara ash dieback.
Bark lesion
A localized area of diseased or damaged tissue on a tree's bark, often appearing as a sunken or discoloured patch.
Protist
A eukaryotic organism (usually unicellular) that is the pathogen causing malaria.
Vector
An organism that carries a pathogen from one host to another without being infected by the disease itself.
Anaemia
A condition caused by a deficiency of red blood cells, resulting in tiredness due to a reduced capacity to transport oxygen.
