EduNinja
[Maximum number: 8]

Osmoregulation is the control of the water potential of body fluids such as blood.

(a)

Osmoreceptors and antidiuretic hormone (ADH) have an important role in osmoregulation.

[ 3 ]
(i)

Name the location of osmoreceptors.

[ 1 ]
(ii)

State the stimulus that is detected by osmoreceptors.

[ 1 ]
(iii)

Name the structure that secretes ADH into the blood.

[ 1 ]
(b)

ADH acts on the cells of the collecting duct, resulting in changes in the volume and concentration of urine.

Fig. 1.1 shows the relationship between the concentration of ADH in the blood and the rate of production of urine by the kidneys.

Fig. 1.1

Fig. 1.1

[ 5 ]
(i)

As the concentration of ADH in the blood increases, the rate of production of urine decreases.

Using Fig. 1.1, calculate the percentage decrease in the rate of production of urine between ADH concentrations of 1 and 3 arbitrary units.

Show your working.
Give your answer to one decimal place.
answer =

[ 2 ]
(ii)

Explain the relationship shown in Fig. 1.1.

[ 3 ]
(a)

The cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. Describe and explain how these cells are adapted to carry out selective reabsorption.

[ 4 ]
(a)

The volume and water potential of the urine produced by the kidney vary according to the water potential of the blood. This is a result of osmoregulation.

Describe the role of aquaporins in osmoregulation.

[ 3 ]
(b)

Describe the role of the brain in osmoregulation when the water potential of the blood increases above the set point.

Question 2 starts on page 5.

[ 3 ]
(a)

The water potential of mammalian blood needs to be maintained within narrow limits so that cells function efficiently. This process is called osmoregulation.

The relative medullary thickness (RMT) indicates the proportion of a kidney that is composed of medullary tissue.

 RMT = thickness of medulla  kidney size ×10\text { RMT }=\frac{\text { thickness of medulla }}{\text { kidney size }} \times 10

Table 1.1 shows the relationship between the RMT and the concentration of urine produced by four mammals from different habitats.

Table 1.1

Table 1.1

[ 3 ]
(i)

Name the parts of the nephron that are located in the medulla.

[ 2 ]
(ii)

Name a hormone involved in osmoregulation.

[ 1 ]
(b)

The warthog, Phacochoerus africanus, is a member of the pig family. The warthog lives in dry savannah areas of sub-Saharan Africa.

Fig. 1.1 shows a warthog.

Fig. 1.1

Fig. 1.1

A warthog and a human have similar values of RMT and concentration of urine. A human can survive only a few days without drinking water, whereas a warthog can live for several months without drinking water.

Suggest how a warthog is able to survive several months without drinking water.

[ 2 ]
[Maximum number: 1]

The jaguar, Panthera onca, is a large cat that lives mainly in South America. The majority of jaguars have light brown fur with black spots, as shown in Fig. 1.1. Some jaguars have completely black fur, as shown in Fig. 1.2.

Fig. 1.1

Fig. 1.1

Fig. 1.2

Fig. 1.2

(a)

The pigments involved in fur colour are produced as a result of biochemical pathways that take place in cells called melanocytes. These pathways are similar to those that occur in human melanocytes.

The melanocortin 1 receptor (MC1R) is located on the cell surface membrane of melanocytes and is coded for by the MC1R gene.

Fig. 1.3 outlines the processes that occur in jaguar melanocytes.

Fig. 1.3

Fig. 1.3

[ 1 ]
(i)

When MC1R is activated a second messenger is produced in the cell.

Give an example of a second messenger.

[ 1 ]
(a)

Fig. 1.1 is a diagram of a kidney nephron and some of its blood vessels.

Fig. 1.1

Fig. 1.1

With reference to Fig. 1.1, complete Table 1.1 using the letters A - G.
Each letter may be used once, more than once or not at all.

Table 1.1

Table 1.1

[ 4 ]
(b)

Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption.

[ 5 ]
(c)

Fig. 1.2 shows the concentrations of ADH in the blood at different percentage changes in water potential of the blood.

Fig. 1.2

Fig. 1.2

[ 2 ]
(i)

Describe the trend shown in Fig. 1.2.
(ii) Sometimes a person will have a low concentration of ADH in the blood even though there is a change in the water potential.

Suggest one effect on the circulatory system of a low concentration of ADH in the blood.

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[ 2 ]
(a)

The Bowman's capsule of a nephron is involved in ultrafiltration.
Fig. 1.1 is a diagram of part of a Bowman's capsule and glomerulus.

Fig. 1.1

Fig. 1.1

With reference to Fig. 1.1, complete Table 1.1 using the letters A - F.
Each letter may be used once, more than once or not at all.

Table 1.1

Table 1.1

[ 4 ]
(b)

Describe and explain how the structures in the Bowman's capsule and its associated blood supply are adapted to allow ultrafiltration to take place.

[ 5 ]
(c)

The glomerular filtration rate (GFR) is the rate at which blood plasma is filtered in the Bowman's capsule.

Fig. 1.2 shows the relationship between GFR and mean renal arterial blood pressure.

Fig. 1.2

Fig. 1.2

[ 3 ]
(i)

Comment on the relationship between GFR and mean renal arterial blood pressure.

[ 2 ]
(ii)

Suggest one reason why the GFR of a person might decrease.

Question 2 starts on page 6.

[ 1 ]
(a)

Fig. 1.1 is a diagram of a kidney nephron and some of its blood vessels.

Fig. 1.1

Fig. 1.1

With reference to Fig. 1.1, complete Table 1.1 using the letters A - G.
Each letter may be used once, more than once or not at all.

Table 1.1

Table 1.1

[ 4 ]
(b)

Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption.

[ 5 ]
(c)

Fig. 1.2 shows the concentrations of ADH in the blood at different percentage changes in water potential of the blood.

Fig. 1.2

Fig. 1.2

[ 3 ]
(i)

Describe the trend shown in Fig. 1.2.

[ 2 ]
(ii)

Sometimes a person will have a low concentration of ADH in the blood even though there is a change in the water potential.

Suggest one effect on the circulatory system of a low concentration of ADH in the blood.

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Turn over for Question 2
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[ 1 ]
(a)

ALT can leak into the blood from liver tumour cells.

An increase in the concentration of ALT in the blood causes a decrease in the water potential of the blood.

State precisely the name and location of the cells where a change in the water potential of the blood would be detected.

[ 1 ]
(b)

Describe the homeostatic role of ADH when the water potential of the blood decreases.

[ 5 ]
(a)

In mammals, the hormone ACTH is released from the anterior pituitary gland. ACTH stimulates the cells of the adrenal glands to synthesise the hormone cortisol. This is an example of cell signalling.

The main stages of cell signalling involving ACTH are similar to the main stages of cell signalling by adrenaline.

Describe the main stages of cell signalling involving ACTH.

[ 5 ]
(b)

If the concentration of cortisol in the blood increases above its set point, it will inhibit the production of ACTH by the anterior pituitary gland.

Name this type of homeostatic mechanism.

[ 1 ]
(c)

One symptom of Cushing's disease in a dog is that the dog will want to drink much more than normal.

Suggest one other reason why a dog would want to drink much more than normal.

[ 1 ]
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