AQA A-LEVEL BIOLOGY ESSAY: THE IMPORTANCE OF RESPONSES TO YOUR INTERNAL AND EXTERNAL ENVIRONMENT
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Course
Alevel biology (7402)
Institution
Uppingham School
Top mark AQA A-level biology essay on The Importance Of Responses To your Internal And External Environment. scored 22/25
includes homeostasis, osmoregulation, immunity, and control of heart rate
Useful for revision for this specific topic and to see a sample structure of a high grade essay.
The Importance Of Responses To Your Internal and External Environment
22/25
Homeostasis is an important process in the maintenance of a human’s internal
environment. It is an example of a negative feedback mechanism in the body. Blood
glucose concentration can increase following eating a carbohydrate-rich meal which
has lots of starch. This is then hydrolysed by amylase into maltose which is then
broken down by maltase into glucose. These glucose molecules are absorbed into
the bloodstream in the ileum. Beta cells in the islets of Langerhans in the pancreas
detect an increase in blood glucose concentration. Beta cells then release insulin.
Insulin is an important hormone responsible for lowering high levels of blood
glucose. Insulin does this by attaching to receptors on the liver cells cell membrane.
Insulin is complementary in tertiary shape to these receptors. When insulin binds, it
changes the shape of those proteins embedded within the membrane of liver cells, it
increases the permeability of muscle cell membranes to glucose by increasing the
number of channel proteins of muscle cell membranes to glucose, so cells absorb
more glucose. Insulin also activates enzymes in muscle and liver cells that convert
glucose into glycogen in a process called glycogenesis. This is important because
glycogen is insoluble so has no osmotic effect on cells whereas glucose does affect
water potential in cells. It is important to bring down high glucose levels because
high blood sugar levels for long periods of time can result in permanent damage to
parts of the body such as the eyes, kidneys, and blood vessels. This is caused by
more glucose being dissolved in blood which lowers blood water potential, so water
leaves the surrounding cells down a water potential gradient via osmosis. This
increases the volume of blood which leads to high hydrostatic pressure.
Hyperglycaemia can cause blurred vision, cataracts, and damage to the retina as the
eyes well and shrink from changes in water potential leading to blurred vision.
Osmoregulation in the kidneys is another important mechanism in controlling an
organism’s internal environment, in this case, water levels. Water levels can fluctuate
because of water in diet, sweating or diabetes. To detect these changes,
osmoreceptors in the hypothalamus either stretch or shrivel as water moves in or out
via osmosis. If water levels are too low, this causes the hypothalamus to produce
more Anti Diuretic Hormone (ADH) which travels to the pituitary gland where it is
released into the blood. The ADH increases the permeability of the collecting duct
wall and the distal convoluted tubule wall by embedding more aquaporins into the
membranes, so more water is reabsorbed from the filtrate in the nephron back into
the blood, resulting in more concentrated urine. It is important that blood water
potential is maintained because if there is too little water, you end up with more
concentrated blood. Water is an important component of the blood as it is a
metabolite and is needed in reactions such as hydrolysis. It is also needed for sweat
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