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AQA A-Level Biology Cause of Human Disease Essay
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There are many causes of human disease, from environmental factors to genetic factors. This essay covers topics such as HIV, helper t-cells, mitosis, and cancer.
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Cause of human diseaseThere are many causes of human disease, from environmental factors, to genetic factors. Disease
can spread between humans easily in many ways, such as through the air, via animals/insects, by
direct contact, and through food.
One of the main causes of disease in humans are bacteria and viruses. Microbes such as fungi
and toxins can also contribute to human disease, but this is less common as most fungi is
harmless and humans tend to steer clear of toxic substances known to be deadly to the human
body. Bacteria are single-celled organisms, these are taken into the body when breathing, eating or
even through breaks/cuts in the skin. Viruses need hosts, which are other living cells, in order to
multiply. If these microbes are able to break through the outer barrier, skin, the body has an innate
immune system response, including the role of white blood cells called T-cells, these look for
foreign antigens and become activated to destroy the cell in which they belong.
HIV however replicates inside the helper T-cells of the host. On it’s spherical structure, HIV is
coated in attachment proteins which helps the HIV attach to the receptor molecule on the cell
membrane of the host helper T-cell. The capsid, which is an outer coating of protein, uncoats and
releases it’s genetic material into the cell’s cytoplasm. Inside the cell reverse transcription takes
place and the HIV takes over the cell. When the helper T-cell numbers reach a critically low level,
this is when people develop acquired immune deficiency syndrome (AIDS).
Usually cells can multiply without viruses interfering, ordinary body cells multiplying is a process
called mitosis. Egg and sperm cells however are produced through meiosis. This process begins
with each of the cells chromosomes duplicating and joining at the centromere, the chromosomes
then pair and crossing over occurs. The chromosomes line up in the metaphase stage and are
pulled to opposite ends by spindle fibres, which their centromere is attached to. The cell then
divides, it eventually produces four genetically different daughter cells. Down’s Syndrome is a
disease in humans caused by an extra copy of chromosome 21, this usually happens when the
chromosome doesn’t separate properly. Having an extra chromosome changes how the cell
functions, as there are extra genes present.
Cancer is also a genetic disease, it is a tumour that invades surrounding tissue and is the result of
uncontrolled cell division. Normally cells stop dividing enough to make new cells, but if there’s a
mutation in a gene that controls cell division, the normal body cells can grow out of control. Risk
factors of causing cancer in humans can include a bad diet, sun exposure, alcohol, or being
overweight. Smoking is also a major cause of cancer in humans, as this can result in lung cancer.
Another disease that affects lungs is emphysema. This disease in humans is caused by smoking,
or long-term exposure to air pollution. Basically, foreign particles become trapped in the alveoli, this
causes inflammation which attracts phagocytes to the area. The phagocytes produce an enzyme
which breaks down elastin, meaning ultimately the alveoli aren’t as elastic and therefore can't
recoil to expel air as well. Lung cancers and respiratory infections made the second largest killer in
2012, while heart attacks and strokes are the main leading causes of death worldwide, making up
60% of deaths.
In conclusion, while bacteria and viruses are the main cause of human disease, genetic faults in
the body can also cause diseases such as Down’s Syndrome and cancer. Environmental factors
and lifestyle choices such as your diet, exercise, air pollution and smoking can cause diseases like
lung cancer in humans.
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