AQA A-LEVEL BIOLOGY ESSAY: THE IMPORTANCE OF THE CONTROL OF PROCESSES IN ORGANISMS
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Module
AQA A-level Biology (7402)
Institution
Uppingham School
Top mark AQA A-level Biology essay on The Importance Of Control Of Processes In Organisms.
Includes transcription factors, ADH, Homeostasis, and plant tropisms
Useful for revision for this specific topic and to see a sample structure of a high grade essay.
THE IMPORTANCE OF CONTROL OF PROCESSES IN ORGANISMS
Transcription factors are important in controlling the process of transcription and
whether a gene should be transcribed. Transcription is when a gene is copied from
DNA into messenger RNA. The enzyme responsible for synthesising mRNA from
DNA is called RNA polymerase. Not all the genes in a cell are expressed because
different genes are expressed, different proteins are made, and these proteins
modify the cell. It is important to control the proteins that a cell makes so that it can
become specialised by determining the cell structure and controlling the cell’s
processes. Controlling a cell’s transcription can also stop a waste of resources like
ATP if cells are transcribing genes that they don’t need. Oestrogen is a steroid
hormone that can affect transcription by binding to a transcription factor called an
oestrogen receptor, forming an oestrogen-oestrogen receptor complex. The complex
moves from the cytoplasm into the nucleus where it binds to specific DNA sites near
the promotor of the target gene. This activates transcription by helping RNA
polymerase bind to the promotor. An example of transcription factors that show their
importance is in the context of cancer. Cancer results from mutations in genes that
regulate and control mitosis. Tumours can develop by increased oestrogen
concentrations. Increased oestrogen concentrations mean it could bind and activate
transcription factors involved in cell division, this would mean that the gene coding
for cell division would be permanently turned on resulting in uncontrolled cell
division. If cell division is not controlled this can lead to tumours.
ADH is important in controlling the process of osmoregulation in the blood. Blood
water potentials can fluctuate due to water in diet, diabetes, or exercise. It is
important to control the concentrations of water to prevent blood water levels from
becoming too high which can increase blood pressure which can cause damage to
the endothelium of blood vessels, leading to tears, blood clots, stroke, or heart
attack. 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 controls the
extent of reabsorption of water in the kidney by increasing 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 to provide a cooling effect due to its high latent heat of vaporisation.
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