Homeostasis (A Level only) (AQA A Level Biology)

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.

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.

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

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.

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.

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.

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.

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.

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

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.

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:

• The rats were divided into three groups for different treatments.
• The rats were given the same food for 5 days beforehand.
• Each of the rat groups were given a dose of treatment; either gallic acid (GA), an established drug called hydrochlorothiazide (HCTZ), or a placebo (containing no active chemicals).
• The researchers then measured the volume of urine produced over a period of 8 hours after treatment.
• They calculated the urine volume per 100g of rat body mass and worked out the mean volume for each group, leaving any anomalies out of their calculations.

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.

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

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.