Define the term homeostasis.
One of the systems involved with homeostasis is the endocrine system.
Explain how the endocrine system functions to bring about responses in the body.
Homeostatic mechanisms work to regulate body temperature in mammals.
Explain why the regulation of body temperature is important.
Body temperature is regulated by a mechanism known as negative feedback.
State how a negative feedback mechanism works.
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Give one reason why blood glucose regulation is important.
Figure 1 below shows some of the events that take place during the regulation of blood glucose.
Figure 1
Identify organ X in Figure 1.
Insulin is released when blood glucose levels rise above normal. The effects of insulin cause blood glucose levels to return to normal levels.
Describe two of the effects of insulin that lead to a fall in blood glucose.
When blood glucose levels fall after exercise, organ X releases another hormone, hormone Y. The effects of hormone Y cause an increase in blood glucose.
Name hormone Y and describe one way that it causes blood glucose levels to return to normal.
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Table 1 below shows some doctor’s notes for a patient with diabetes.
Table 1
|
Patient age |
9 |
|
Symptoms |
More thirsty than usual Increased urine production Weight loss Fatigue |
|
Cytotoxic T cell activity |
High |
|
Suggested treatment |
Blood glucose monitor Insulin injections by pump |
Identify whether the patient in Table 1 is likely to have type 1 or type 2 diabetes. Explain your answer.
A doctor has recommended that the patient in Table 1 should monitor their glucose and has prescribed insulin injections.
Explain this treatment choice.
One way of assessing a patient’s risk of diabetes is to test their urine for the presence of glucose.
Name and describe the test that could be used to test for the presence of glucose in urine.
The test described in part c) is qualitative, meaning that it tests for the presence of glucose but doesn’t provide a numerical measure for glucose concentration.
Describe how the glucose concentration of a urine sample could be estimated after carrying out the test described in part c). Your described method should avoid issues with human interpretation of colour intensity.
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Figure 1 below shows a diagram of a kidney nephron.
Figure 1
Identify the structures labelled A-C in Figure 1.
Identify one feature of structure A in Figure 1, which enables ultrafiltration to take place. Explain how it aids ultrafiltration.
After ultrafiltration the filtrate enters the proximal convoluted tubule (PCT), as labelled in Figure 1. Name the process that takes place in the PCT.
Table 1 below contains descriptions and explanations of various features of the PCT from Figure 1 that assist with the process identified in part c).
Table 1
|
Adaptive feature |
How feature helps PCT with function |
|
Cells lining the PCT have microvilli |
1 |
|
The PCT is a long tube with many folds. |
Increases surface area of PCT |
|
Co-transporter proteins in the surface membranes of cells lining the PCT |
2 |
|
Cells lining the PCT contain many mitochondria |
3 |
Fill in the gaps labelled 1-3 in Table 1 to finish explaining the adaptive features of the PCT.
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Define the term osmoregulation.
The paragraph below describes some of the events that take place when blood water content decreases.
A group of cells called osmoreceptors, located in the ___(1)___ of the brain, detect changes in blood water potential. If the water potential of the blood decreases, water moves ___(2)___ the osmoreceptors, causing them to ___(3)____ in size. This change in size of the osmoreceptors stimulates the ____(4)_____ to release a hormone called ADH.
Fill in the gaps labelled 1-4 in the paragraph above. You may use one word per gap, or more than one word.
State the effect that the hormone ADH has on the kidneys.
Explain how the effect stated in part c) helps to restore normal water balance in the body after a reduction in the water potential of the blood as described in part b).
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A group of scientists wanted to investigate the control of blood glucose in mice. They fed one group of mice with a normal diet and another group with a ‘high fat’ diet (containing a high level of both fat and sugar) for three weeks beforehand. They then measured their blood glucose over a period of 2 hours directly after a meal. Their results are shown in Figure 1 below.
Figure 1
Explain the change in blood glucose levels shown in Figure 1 for the normal diet mice during the first 90 minutes after the meal.
After the first 90 minutes, the normal diet mice show an increase in blood glucose despite no more food being eaten. This is due to the action of a hormone called glucagon, which initiates the production of glucose in the cells. Describe how glucagon enables the production of glucose inside cells.
At the same time as measuring blood glucose, the scientists also measured blood insulin levels. Their results are shown in Figure 2 below.
Figure 2
Use the information in Figure 2 to suggest an explanation for the difference in blood glucose changes between the two groups of mice shown in Figure 1.
The scientists then gave the high fat diet mice supplements of a drug called a DDP-4 Inhibitor in their drinking water. The effects of the DDP-4 enzyme in the body are shown in Figure 3.
Figure 3.
Use the information provided in Figure 3 to suggest and explain how the administration of DDP-4 inhibitors might affect the blood-glucose levels of the high fat diet mice.
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The glomerulus is a structure in the kidneys responsible for the process of ultrafiltration.
Explain how ultrafiltration would be affected by severe dehydration.
An important role of the kidneys is the removal of urea from the blood. The amount of urea removed from the blood can be used as a measure of the rate of ultrafiltration, also known as the glomerular filtration rate (GFR).
An individual excretes 540 mg of urea in their urine over the course of 1 hour, and has a blood urea concentration of 0.01 mg cm-3 entering the kidneys. Use this information to calculate this person’s GFR. Give your answer in cm3 min-1.
After ultrafiltration, the filtrate travels through the kidney nephron. Figure 1 shows what happens to various components of the filtrate as they move through the different parts of an individual’s nephron.
Figure 1
Describe and explain the shape of the curve for sodium ions and water as they travel through region 2 of the nephron in Figure 1.
Explain how the line for water in region 4 of Figure 1 would look different if the ADH concentration in this individual’s blood decreased.
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Table 1 below contains several examples of drugs used to treat diabetes, together with a brief description of each drug’s mechanism of action.
Table 1
|
Name of drug |
Effect on the body |
Mechanism of action |
|
Metformin |
Disrupts the structure of cAMP and protein kinase A |
|
|
DPP-4 inhibitors |
Increases levels of hormone GLP-1 |
GLP-1 is involved with increasing insulin secretion and reducing glucagon secretion. |
|
Acarbose |
Competitive inhibitor of pancreatic amylase |
|
|
SGLT2 inhibitors |
Inhibit sodium-glucose cotransporters in the proximal convoluted tubule |
The mechanism of action for DPP-4 inhibitors has been provided in Table 1. Use the information in the table to suggest an explanation for the mechanism of action of metformin, acarbose, and SGLT2 inhibitors.
Nitric oxide (NO) is a chemical released by the blood vessel lining that causes dilation of the blood vessels. A group of researchers looked at the levels of Nitric oxide in a control group of rats and in a group of diabetic rats (DR) at different blood glucose concentrations. Some of their results are shown in Figure 1.
Figure 1
Describe and explain the difference in blood glucose between the control rats and the diabetic rats shown in Figure 1.
In humans, long-term diabetes with greatly elevated blood glucose is a leading cause of kidney disease, one symptom of which is protein found in the urine.
Use the information provided in part b) as well as Figure 1 to suggest an explanation for the mechanism by which diabetes causes kidney disease.
Diabetes is also connected with increased urine production. Other than the possible effects of NO, suggest why high blood glucose leads to a higher volume of urine being produced.
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Oedema is a medical condition in which the body retains water, leading to swelling of the limbs. A group of scientists wanted to test the diuretic efficacy of a plant compound called gallic acid in the hope that it could become a future treatment for oedema.
They carried out their experiment on rats. Their method included the following measures:
Some of their results are shown in Figure 1.
Figure 1
* = mean result is significantly different from the placebo group mean
Explain three measures taken by the researchers to ensure that their results were valid.
State what can be concluded from Figure 1 about the effectiveness of GA in the treatment of oedema in humans.
Figure 2 below shows the mechanism of action of HCTZ diuretics.
Figure 2
Use Figure 2 to explain the effect of HCTZ on urine volume shown in Figure 1.
Some research has shown a possible connection between the use of HCTZ medication and an increase in insulin resistance (when the body cells don’t respond to insulin).
Suggest why some doctors are hesitant to prescribe HCTZ despite their effectiveness at regulating blood water content.
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Organisms that live in a saltwater environment face extreme osmoregulatory challenges. Suggest why it is so difficult for marine mammals to maintain the correct osmotic balance in their blood.
Table 1 contains information about several marine mammals and their osmoregulatory Mechanisms. Humans have been added for comparison purposes, and seawater sodium concentration has also been included.
Table 1
|
Organism |
Habitat |
Primary water source |
Urine osmolarity / mosmol L-1 |
Na+ concentration / mmol L-1 |
|
Human |
Terrestrial |
Drinking freshwater |
1400 |
20 |
|
West Indian Manatee |
River (but can survive in marine) |
Diet / metabolism |
1158 |
31 |
|
Sea otter |
Marine |
Drinking seawater |
2130 |
505 |
|
Elephant seal |
Marine |
Diet/metabolism |
1850 |
297 |
|
Seawater |
N/a |
N/a |
N/a |
470 |
Suggest how sea otters are able to drink seawater and still maintain osmotic balance.
Manatees are unusual marine mammals in that they are able to spend time in both salt- and freshwater environments. Research into osmoregulation in manatees shows that levels of a hormone called aldosterone change when the manatee’s environment changes. Aldosterone is known to activate a sodium transporter protein in the cells lining the kidney tubule.
Suggest how the salt- and freshwater environments might affect aldosterone levels and explain how this could help the manatee regulate its ion balance.
Sea birds do not osmoregulate in the same way as marine mammals. They excrete nitrogenous waste via highly concentrated uric acid, and excrete excess salt separately via salt glands. Figure 1 shows the structures within the salt glands, where a countercurrent mechanism involving capillaries and salt secretory tubules removes excess salt to an external secretory duct.
Figure 1
Suggest how the countercurrent system ensures maximum salt excretion from the blood of sea birds.
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The control of water and glucose levels in the body involves negative feedback loops.
Describe what is meant by a negative feedback loop.
Name three ways in which water is removed from the body.
Figure 1 shows the cells lining the collecting duct in a human kidney. ADH molecules released from the pituitary gland bind to the receptor proteins of the collecting duct cells. This triggers vesicles containing aquaporins to bind with the plasma membrane next to the lumen.
Figure 1
Using the information above, explain how ADH increases the net movement of water from the lumen of the collecting duct into the blood.
Hormones travel to all areas of the body through the blood but they only affect specific target cells. Explain how.
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Explain how the maintenance of a constant body temperature in humans allows for metabolic reactions within cells to proceed at maximum efficiency.
Some diabetic individuals do not produce insulin. In an experiment, a woman with diabetes drank a sugary solution. The glucose concentration in their blood was measured at regular intervals. The results are shown in Figure 1 below.
Figure 1
Suggest three reasons why the concentration of glucose decreased after 60 minutes even though this woman’s blood contained no insulin.
The same experiment was repeated on a non-diabetic woman. The glucose concentration in their blood prior to drinking the sugary solution was 75 mg per 100 cm3. Sketch a curve on Figure 1 to show the results you would predict.
High blood pressure is a possible side effect of poorly controlled diabetes. Use your knowledge of osmosis to explain why.
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The molecules glucagon and glycogen are both involved in regulating blood glucose concentration. Explain the different roles they play.
The cells of individuals with type II diabetes exhibit low sensitivity to the protein insulin. Roughly 76% of people with type II diabetes are classed as obese or overweight. Some obese individuals are offered gastric bypass surgery by the NHS to aid weight loss.
Researchers investigated whether gastric bypass surgery affected cells' insulin sensitivity. The individual's sensitivity to insulin was measured both before and after gastric bypass surgery. Individuals getting the surgery fell into three groups, they either had type II diabetes, were prediabetic or had no diabetes.
Table 1 below shows the results. The larger the number, the greater the sensitivity to insulin.
Table 1
|
Individuals receiving the surgery |
Mean sensitivity to insulin (± SD) |
|
|
Before surgery |
1 month post surgery |
|
|
Group 1 |
0.55 (± 0.32) |
1.30 (± 0.88) |
|
Group 2 |
1.07 (± 0.29) |
1.39 (± 0.58) |
|
Type II Diabetics |
0.40 (± 0.24) |
1.10 (± 0.87) |
Use the data in Table 1 to suggest which groups were prediabetic and non-diabetic. Explain your answer.
The researchers also stated that gastric bypass surgery cured several individuals’ diabetes but that some individual’s diabetes were not aided very much by the surgery. Does the data support this conclusion? Justify your answer.
Some diabetics have to inject themselves with insulin to keep their diabetes under control. Suggest why insulin has to be injected and cannot be taken orally.
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There are three vital processes involved in the formation of urine within a mammalian kidney. These are ultrafiltration, selective reabsorption and concentration. Describe what occurs during selective reabsorption.
Some mammals living in desert environments have been shown to secrete large amounts of antidiuretic hormone (ADH) and have elongated loops of Henle. Explain how these two features are adaptations to their habitat.
Figure 1 below shows the effect that a loss of the liver and kidney function can have on the urea concentration in the blood.
Figure 1
A research assistant reviewing the data stated that urea was produced in the liver. Does the data in Figure 1 support this statement?
Explain why the concentration of urea stays roughly the same in patient Y for 12 hours.
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Describe the mechanism by which insulin reduces the glucose concentration in the blood.
Adrenaline is produced in times of stress and is described as a “fight or flight” hormone. It can trigger the breakdown of glycogen in the liver. Figure 1 below shows the second messenger model of hormone action that occurs when the liver cells have been stimulated by adrenaline or glucagon.
Figure 1
Explain why it is advantageous for adrenaline to be amplified through a second messenger.
Glucagon is another hormone that can cause an increase in blood glucose concentration. After glucagon is secreted by alpha cells in the pancreas, it breaks down within a matter of minutes. Suggest the benefit of this.
Suggest why it is important that an organism maintains a stable blood pH.
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