14.1. Homeostasis in mammals
A subsection of Biology, 9700, through 14. Homeostasis
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In mammals, excess amino acids cannot be stored in the body. Outline the formation of urea from excess amino acids by liver cells. The mammalian kidney is composed of many nephrons. Describe the process of ultrafiltration in the nephron. is a diagram of a nephron. afferent arteriole efferent arteriole glomerulus proximal convoluted tubule (PCT) loop of Henle distal convoluted tubule (DCT) collecting duct renal capsule Complete Table 7.1 by naming a part of the nephron that corresponds to each of the statements. Table 7.1 statement part of nephron passes through the medulla glucose is reabsorbed into the blood ADH acts on its walls most of the water is reabsorbed into the blood
9700_s16_qp_42
THEORY
2016
Paper 4, Variant 2
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The enzyme alanine transaminase (ALT) is found in the liver. The function of ALT is to convert the amino acid α-ketoglutarate into another amino acid, glutamate. Suggest why the liver may need to convert one amino acid into another. Tumours can form in the liver. Explain how a liver tumour develops. 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. Describe the homeostatic role of ADH when the water potential of the blood decreases.
9700_s20_qp_42
THEORY
2020
Paper 4, Variant 2
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Urea is the main nitrogenous waste product in humans. It is made in the liver and excreted by the kidneys in urine. Define the term excretion. The kidneys regulate the water potential of body fluids. This is known as osmoregulation and involves a negative feedback system. Outline the role of negative feedback in osmoregulation. Investigations have shown that when a person remains in a cold environment for more than 15 minutes there is increased urine production. This is called cold diuresis. Suggest how exposure to cold can lead to cold diuresis.
9700_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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Blood glucose concentration is maintained around a set point by homeostasis. Explain the principles of homeostasis. Glycogen phosphorylase catalyses the conversion of glycogen to glucose in liver cells. The production of glycogen phosphorylase is coded for by the gene PYGL. A mutation in PYGL leads to a condition called glycogen storage disease type VI (GSD, in which glycogen is not broken down efficiently. Suggest and explain why cell signalling by glucagon is likely to be affected in the liver cells of a person with GSDVI. The boundaries and names shown, the designations used and the presentation of material on any maps contained in this question paper/insert do not imply official endorsement or acceptance by Cambridge Assessment International Education concerning the legal status of any country, territory, or area or any of its authorities, or of the delimitation of its frontiers or boundaries. Glycogen synthase catalyses the conversion of glucose to glycogen in liver cells. The production of glycogen synthase is coded for by the gene GYS2. A mutation in GYS2 leads to a condition called glycogen storage disease type 0 (GSD0) in which glycogen is not formed efficiently. Suggest what the consequences would be if a person with GSD0 has a meal rich in glucose.
9700_w24_qp_42
THEORY
2024
Paper 4, Variant 2
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shows diagrams of nephrons from the kidneys of three different mammals, P, Q and R. These are all drawn to the same scale. P Q urine with high water potential urine with low water potential urine with very low water potential R State the relationship between the length of the loop of Henle and the water potential of the urine of the three mammals. The nephron of a camel is similar to that of mammal R. Suggest why it is important that the camel produces urine with a very low water potential. The epithelial cells of the proximal convoluted tubule are adapted to carry out selective reabsorption. Table 1.1 lists three features of epithelial cells of the proximal convoluted tubule. For each feature, explain how it helps the process of selective reabsorption. Table 1.1 feature explanation microvilli many mitochondria tight junctions between cells
9700_m17_qp_42
THEORY
2017
Paper 4, Variant 2
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is a drawing of a longitudinal section (LS) of a human kidney. D A B C Use the letters A, B, C and D in to complete Table 1.1. Each letter may be used once, more than once or not at all. For each description, list all the letters that are correct. Table 1.1 description region of kidney location of loops of Henle location of Bowman’s capsules location of glomeruli contains urine at final concentration 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. Describe the role of the brain in osmoregulation when the water potential of the blood increases above the set point.
9700_m23_qp_42
THEORY
2023
Paper 4, Variant 2
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is a diagram of a nephron. Label using: • one labelling line and the letter A to identify a region that contains urine • one labelling line and the letter B to identify a region that contains podocytes • one labelling line and the letter C to identify a region of the nephron that is within the medulla of the kidney • one labelling line and the letter D to identify the afferent arteriole. 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.
9700_m24_qp_42
THEORY
2024
Paper 4, Variant 2
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Use During the process of the excretion of nitrogenous waste in mammals, blood passes from the renal artery into networks of capillaries called glomeruli. is an electronmicrograph showing the relationship between the capillaries and the renal capsule cells, called podocytes. Name structures A and B. A B Draw an arrow, on , to show the passage of fluid out of the capillary. Name the fluid that collects in the capsular space. Describe how the composition of this fluid differs from blood plasma. Examiner’s Use Ultrafiltration involves the removal of small molecules, including urea, from the blood into the renal capsule. Explain what is required for ultrafiltration to occur.
9700_s06_qp_4
THEORY
2006
Paper 4, Variant 0
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Questions Discovered
95