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14. Homeostasis
A section of Biology, 9700
Listing 10 of 131 questions
One important function of the kidney nephron is selective reabsorption. This involves the rapid transfer of water across cell surface membranes. The rapid transfer of water requires the presence of protein channels known as aquaporins. is a diagram of a nephron. $ % & ' - + * ( ) With reference to , complete the table by inserting the correct letter for each description. description of region of nephron letter region where no aquaporins are present in the tubule wall cells region where aquaporins and glucose transport proteins are present in tubule wall cells region where aquaporins are always present in the tubule wall cells but no glucose transport proteins are present region where tubule wall cells are modified to produce filtration slits The urine of people on different types of diet was analysed. • people on a low protein diet had a mean urea concentration of 2.40 g dm–3 • people on a high protein diet had a mean urea concentration of 14.76 g dm–3. Calculate the percentage increase in the concentration of urea between the low and high protein diets. Show your working. answer % Explain why an increase in the quantity of protein in the diet leads to an increase in the concentration of urea in the urine.
9700_w15_qp_43
THEORY
2015
Paper 4, Variant 3
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is a diagram of a kidney nephron and some of its blood vessels. B C G A F D E With reference to , 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 description letter efferent blood vessel part of nephron containing cells that respond to ADH part of nephron where podocyte cells are located part of nephron containing cells that are located in the medulla Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. shows the concentrations of ADH in the blood at different percentage changes in water potential of the blood. 0– 20 – 10 +10 percentage change in water potential of the blood concentration of ADH in the blood / arbitrary units Describe the trend shown in . 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.
9700_w21_qp_41
THEORY
2021
Paper 4, Variant 1
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is a diagram of a kidney nephron and some of its blood vessels. B C G A F D E With reference to , 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 description letter efferent blood vessel part of nephron containing cells that respond to ADH part of nephron where podocyte cells are located part of nephron containing cells that are located in the medulla Describe and explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. shows the concentrations of ADH in the blood at different percentage changes in water potential of the blood. 0– 20 – 10 +10 percentage change in water potential of the blood concentration of ADH in the blood / arbitrary units Describe the trend shown in . 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.
9700_w21_qp_43
THEORY
2021
Paper 4, Variant 3
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is a diagram of a kidney nephron. Bowman’s capsule collecting duct renal pelvis medulla B A C With reference to , name A, B and C. A B C Antidiuretic hormone (ADH) is involved in the maintenance of the water potential of the blood. shows the relationship between blood ADH concentration, urine concentration and the flow rate of urine. The flow rate of urine is the rate of production of urine by the kidneys. blood ADH concentration / arbitrary units urine flow rate / cm3 min–1 urine concentration / mmol dm–3 urine flow rate urine concentration Key Describe the relationships shown in . Describe and explain the action of ADH on the cells of the collecting duct when the water potential of the blood decreases.
9700_w22_qp_41
THEORY
2022
Paper 4, Variant 1
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Selective reabsorption takes place in the proximal convoluted tubule of a kidney nephron. is a diagram of two cells of the proximal convoluted tubule and part of the adjacent blood capillary. blood plasma lumen of proximal convoluted tubule proximal convoluted tubule cell The cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. On , use label lines and letters to indicate: • C, where cotransporter proteins are located • P, where sodium-potassium pumps are located. Explain how the cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. The plasma, the glomerular filtrate and urine are composed of various substances. Table 8.1 shows the percentage composition of plasma, the glomerular filtrate and urine. Table 8.1 substance percentage composition plasma glomerular filtrate urine water 90.00 90.00 94.00 glucose 0.10 0.10 0.00 amino acids 0.05 0.05 0.00 plasma proteins 8.00 0.00 0.00 urea 0.03 0.03 2.00 other substances 1.82 9.82 4.00 As a result of the action of the cells of the proximal convoluted tubule, glucose and amino acids have been reabsorbed by the blood, whereas only some of the urea has been reabsorbed. Calculate how many times the percentage composition of urea has increased in the urine compared with the glomerular filtrate. Show your working and give your answer to the nearest whole number. answer
9700_w22_qp_42
THEORY
2022
Paper 4, Variant 2
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is a diagram of a kidney nephron. Bowman’s capsule collecting duct renal pelvis medulla B A C With reference to , name A, B and C. A B C Antidiuretic hormone (ADH) is involved in the maintenance of the water potential of the blood. shows the relationship between blood ADH concentration, urine concentration and the flow rate of urine. The flow rate of urine is the rate of production of urine by the kidneys. blood ADH concentration / arbitrary units urine flow rate / cm3 min–1 urine concentration / mmol dm–3 urine flow rate urine concentration Key Describe the relationships shown in . Describe and explain the action of ADH on the cells of the collecting duct when the water potential of the blood decreases.
9700_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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In mammals, the water potential of the blood is constantly monitored by osmoreceptor cells in the hypothalamus of the brain. When the water potential of the blood decreases, ADH (antidiuretic hormone) is produced by cells in the hypothalamus and released into the blood via an endocrine gland. Explain what is meant by the term water potential. Describe the effect on water potential of adding solute to a solution. State precisely where ADH is released into the blood. The decrease in the water potential of the blood is sometimes due to the loss of water from the body of a mammal. List two ways by which water may be lost from the body. Describe the action of ADH on the kidney. Diabetes insipidus is a condition caused by an inability to produce ADH or by the kidneys being unable to respond to ADH. Suggest symptoms that may be experienced by a person who has diabetes insipidus.
9700_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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Questions Discovered
131