Homeostasis in Mammals (CIE A Level Biology)

Urea is excreted from the body in urine.

Outline why urea is present in the urine.

Fig. 1 shows part of the process of urea production.

Fig. 1

Identify the molecule marked X in Fig. 1.1

[1]

Give one reason why molecule X cannot remain in the blood.

Urea influences the water balance of the blood.

Explain why the control of blood water balance is described as a negative feedback mechanism.

Suggest why it is very important that the water balance of the blood is regulated.

Fig. 1 shows a representation of the structure of a kidney nephron.               

Fig. 1

Identify the structures mark A-C in Fig. 1.

Fig. 2 shows part of the glomerulus of a mouse.

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Fig. 2

Name one feature visible in Fig. 2 that aids the process of ultrafiltration..

[1]

(ii)

Explain the advantage provided by the structure named in part (i).

[1]

Table 1 shows the concentrations of several substances in the blood and in the glomerular filtrate.

Table 1

Calculate the percentage decrease in the concentration of protein between the blood and the glomerular filtrate.

[2]

Other than that shown in Fig. 2, give a reason for the difference calculated in part (i).

[1]

A patient at a medical examination was diagnosed with high blood pressure.

Give two ways in which high blood pressure might affect the ultrafiltration process in the patient's kidneys.

Some diabetic individuals do not produce insulin. In an experiment, a woman with diabetes drank a sugary solution. The glucose concentration in her blood was measured at regular intervals. The results are shown in Fig. 1.

Fig. 1

Suggest two 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 patient. The glucose concentration in their blood prior to drinking the sugary solution was 75 mg per 100 cm³.

Sketch a curve on Fig. 1 to show the results you would predict.

[1]

Outline the reason for the curve that you have sketched in part (i).

[3]

The regulation of glucose is an example of a homeostatic mechanism. Another example of a homeostatic mechanism is osmoregulation.

Describe the role of ADH in osmoregulation.

Some people have a condition called diabetes. In type 1 diabetes the pancreas does not produce enough insulin.

Fig. 1 shows the blood glucose concentrations of a type 1 diabetic person and a non-diabetic person, at regular intervals after drinking a glucose drink.

Fig. 1

Describe the results shown in Fig. 1.

[3]

(ii)

Name the location of the receptors in a non-diabetic person that detect a change in blood glucose concentration.

[1]

(iii)

Name the homeostatic mechanism by which blood glucose concentration is maintained.

The urine of a non-diabetic person does not contain glucose. A person with type 1 diabetes will excrete glucose in urine. 

A reading of the concentration of glucose in the urine can be estimated using a dipstick.

Fig. 2 outlines how a dipstick works.

Fig. 2

The higher the concentration of glucose in the urine, the darker the colour on the dipstick.

Name enzymes A and B.

[2]

(ii)

An electronic biosensor can be used to measure the glucose concentration in a drop of blood.

Suggest one advantage of using a biosensor and one advantage of using a dipstick to measure glucose concentration.

Describe the role played by insulin in the control of blood glucose concentration.

During contraction muscles use up ATP very quickly. For a short period of time ATP can be resynthesised using creatine phosphate, as shown in Fig. 1.

ADP + creatine phosphate → ATP + creatine

Fig. 1

The creatine formed as a result of the resynthesis of ATP is converted to creatinine. Creatinine production in the body stays fairly constant. Creatinine becomes part of the glomerular filtrate during ultrafiltration in the kidney nephrons.

Ultrafiltration requires a high blood pressure in the glomerulus.

Explain how this high blood pressure is achieved.

[1]

Name the main filtration barrier in the nephron that allows creatinine to pass into the Bowman’s capsule but stops red blood cells from passing through.

The concentration of creatinine in the blood largely depends on the glomerular filtration rate (GFR). By measuring the concentration of creatinine in the blood, the GFR can therefore be estimated. The value of the GFR can be used to assess the efficiency of the kidneys.

In humans, a normal value of the GFR is 100 cm³  min^–1.

Fig. 2 shows the relationship between the GFR and the concentration of creatinine in the blood.

Fig. 2

Describe the relationship shown in Fig. 2.

[2]

Use Fig. 2 to estimate the concentration of creatinine in the blood that indicates a normal GFR.

[2]

Suggest two reasons why the GFR of a person might decrease.

[2]

Describe how the structure of the nephron and its associated blood vessels are adapted to the process of ultrafiltration.

Describe the effects of insulin on its main target tissues and explain how this leads to changes in blood glucose concentration.

Insulin is a hormone that affects blood sugar levels.

Explain how insulin affects body cells.

Diabetes is a condition in which the hormone insulin is unable to carry out its function. Metformin is a drug sometimes used to treat diabetes. 

A research group investigated the effect of metformin on blood glucose levels in 10 diabetic mice. The mice were given no food for 12 hours and were then given either no metformin (the control group), a 60 mg per kg dose of metformin, or a 400 mg per kg dose. 30 minutes later the mice were given a glucose meal and 180 minutes after this their blood glucose levels were measured. The results, along with bars to show standard deviation, are shown in Fig. 1.

Fig. 1

A research assistant concluded from these results that metformin was an effective drug for the treatment of diabetes in human patients.

Use Fig. 1 and the information provided to evaluate this conclusion.

The drug metformin works by lowering cellular levels of cyclic AMP.

Suggest how metformin works to reduce the impact of non-functioning insulin.

A simple indicator test for diabetes in a patient involves the use of a urine test strip.

State why urine test strips show the presence of glucose but not other sugars in the urine.

Explain why glucose is present in the urine of diabetic individuals.

[1]

Fig. 1 shows the changing concentrations of several substances as they pass through the regions of the nephron.

Fig. 1

Identify region 1 of the nephron shown in Fig. 1.

[1]

Give a reason for your answer to part (i).

[1]

Region 2 in Fig. 1 is the location at which much of the water is reabsorbed from the filtrate. During the second half of region 2, sodium ions are actively pumped out of the nephron into the surrounding medulla, indicated by a downward curve in Fig. 1.

Suggest how this accounts for the reabsorption of water from region 2.

Fig. 2 shows a micrograph of the lining of region 1 from Fig. 1.

Fig. 2

Identify two features visible in Fig. 2 that aid the process of reabsorption.

[2]

Explain how each of the features identified in part (i) aid reabsorption.

The cells shown in Fig. 2 have many Na⁺/K⁺ transporter proteins in their cell surface membranes.

Explain the role of Na⁺/K⁺ transporter proteins in the reabsorption of nutrients.

The glomerulus is a structure in the kidneys responsible for the process of ultrafiltration.

Explain how ultrafiltration would be affected by severe dehydration.

Ultrafiltration relies on a water potential gradient being established. 

Explain how solute concentration and pressure within the glomerulus establishes a water potential gradient during ultrafiltration.

An important role of the kidneys is the removal of urea from the blood. The volume 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 720 mg of urea in their urine over 1 hour, and has a blood urea concentration of 0.01 mg cm^-3 entering the kidneys. Volume is calculated by dividing mass by concentration.

Use this information to calculate this person’s GFR.  Give your answer in cm³ min^-1.

Diabetes insipidus is a disease partly caused by non-functioning ADH receptor proteins within the membrane of the collecting duct epithelial cells. 

Table 1 shows the concentration of solutes within different structures of the nephron in the presence or absence of ADH. 

Table 1

A doctor wanted to summarise the concentration of solutes with and without ADH present in patients suffering from diabetes insipidus and had to choose whether to summarise the data by calculating the mean, the median or the mode.

Explain what can be concluded about the action of ADH from the data given in Table 1. 

Suggest and explain a symptom of a person with diabetes insipidus. 

In patients with severe diabetes insipidus individuals may be given a synthetic ADH called desmopressin. Patients are warned not to consume too much fluid whilst taking desmopressin. 

Suggest why.