14.1. Homeostasis in mammals
A subsection of Biology, 9700, through 14. Homeostasis
Listing 10 of 95 questions
A tyrosine kinase receptor (TKR) is a protein complex found in the cell surface membrane of mammalian cells. TKR has two components involved in the process of cell signalling: • a receptor for the signalling molecule • an enzyme that catalyses the transfer of a phosphate group from ATP to an intracellular protein. is a diagram to show how TKR is involved in cell signalling. outside cell activated intracellular protein signalling molecule receptor component enzyme component ATP ADP Most enzymes are specific to one reaction. With reference to , explain how the structure of an enzyme provides its specificity. The drug GNF-5 is used in the treatment of some cancers. GNF-5 affects the activity of TKR by binding to the enzyme component of the complex. Researchers investigated the effect of GNF-5 on the activity of TKR using different concentrations of ATP solution. In an experiment the activity of TKR was measured with no GNF-5 and with GNF-5. The results are shown in . 0.1 concentration of ATP / μmol dm–3 activity of TKR / arbitrary units Key with no GNF-5 with GNF-5 The researchers concluded that GNF-5 acts as an inhibitor of the enzyme component of TKR and that it is a competitive inhibitor. Use to provide evidence for these conclusions. A mutation of the gene coding for TKR results in changes to the enzyme component of TKR. This altered form of TKR is known as T315L. The effect of GNF-5 on the activity of T315L was also investigated. The results of this investigation are shown in . 0.1 concentration of ATP / μmol dm–3 activity of T315L / arbitrary units Key with no GNF-5 with GNF-5 Use and to: State how the activity of T315L differs from TKR when no GNF-5 was present. State how the effect of GNF-5 on T315L differs from the effect of GNF-5 on TKR.
9700_s22_qp_21
THEORY
2022
Paper 2, Variant 1
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In mammals, the blood glucose concentration must be maintained within narrow limits so that the body cells can function efficiently. Name the mechanism by which the blood glucose concentration is maintained within narrow limits. Glucagon is released by the alpha (α) cells of the pancreas when the blood glucose concentration decreases below the set point. outlines the response of liver cells to glucagon. receptor glucagon G-protein enzyme A second messenger B activated kinase enzymes enzyme cascade activated glycogen phosphorylase cytoplasm ATP cell surface membrane State how glucagon reaches the liver cells. With reference to , name enzyme A and second messenger B. A B State the role of the enzyme cascade. State the function of the final enzyme in the pathway, glycogen phosphorylase. A biosensor is used to measure blood glucose concentration to check that it is within the normal range. Describe how a glucose biosensor works.
9700_s22_qp_41
THEORY
2022
Paper 4, Variant 1
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Insulin has an important role in the maintenance of blood glucose concentration. An investigation measured how blood glucose concentration and blood insulin concentration changed after a glucose-rich meal had been eaten. The results are shown in . 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 blood glucose concentration / mmol dm–3 blood insulin concentration / pmol dm–3 07.00 08.00 09.00 time of day glucose-rich meal eaten 10.00 11.00 12.00 Key blood glucose concentration blood insulin concentration Describe and explain how the results shown in indicate a relationship between blood glucose concentration and blood insulin concentration after the consumption of a glucose-rich meal. Suggest and explain how the results shown in would change if the meal was mostly starch rather than glucose. 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. Glucagon is synthesised by cells in the pancreas known as alpha (α) cells. Glucagon binds to G-protein-coupled receptors in the cell surface membrane of liver cells. This results in the activation of G-proteins. Outline the sequence of events occurring within the cell after the activation of G-proteins that helps to restore the blood glucose concentration to its set point.
9700_s22_qp_43
THEORY
2022
Paper 4, Variant 3
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The secretion of insulin by the islets of Langerhans in the pancreas stimulates the liver to reduce the blood glucose concentration. Describe how the liver reduces blood glucose concentration, when insulin is secreted. Almost all insulin used to treat type I diabetes is produced by genetically engineered bacteria or yeast. A summary of this procedure is shown in . isolate human insulin gene prepare plasmid vector step 1 step 2 insert gene into vector step 3 insert recombinant vector into bacterium step 4 identify genetically modified bacteria step 5 clone bacteria and extract insulin step 6 One way of carrying out step 1 is to collect mRNA from β cells from the pancreas. The relevant mRNA is then isolated and used to make DNA. Suggest why isolating the mRNA coding for insulin in a β cell is easier than isolating the DNA for insulin in a β cell. Outline the use of restriction enzymes in step 2. Most people with type I diabetes inject insulin. A recent product contains insulin that can be administered using a nasal spray. The spray is inhaled and the insulin is taken up through the lungs. shows the concentration of insulin in the blood plasma in the 480 minutes after injecting or inhaling insulin. In both cases, the insulin was of the same type, obtained from genetically engineered Escherichia coli. insulin concentration in blood plasma / arbitrary units time after administration / minutes × × × × × × × × × × × × × × × × × inhaled insulin injected insulin shows the concentration of glucose in the blood plasma in the 480 minutes after injecting or inhaling insulin. glucose concentration in blood plasma / arbitrary units time after administration / minutes × × × × × × × × × × inhaled insulin injected insulin × Compare the results for injected insulin and inhaled insulin shown in . With reference to , explain the differences in the blood glucose levels after injecting or inhaling insulin shown in . With reference to Figs. 4.2 and 4.3, suggest one advantage and one disadvantage of inhaling insulin rather than injecting it. advantage disadvantage
9700_w10_qp_41
THEORY
2010
Paper 4, Variant 1
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The secretion of insulin by the islets of Langerhans in the pancreas stimulates the liver to reduce the blood glucose concentration. Describe how the liver reduces blood glucose concentration, when insulin is secreted. Almost all insulin used to treat type I diabetes is produced by genetically engineered bacteria or yeast. A summary of this procedure is shown in . isolate human insulin gene prepare plasmid vector step 1 step 2 insert gene into vector step 3 insert recombinant vector into bacterium step 4 identify genetically modified bacteria step 5 clone bacteria and extract insulin step 6 One way of carrying out step 1 is to collect mRNA from β cells from the pancreas. The relevant mRNA is then isolated and used to make DNA. Suggest why isolating the mRNA coding for insulin in a β cell is easier than isolating the DNA for insulin in a β cell. Outline the use of restriction enzymes in step 2. Most people with type I diabetes inject insulin. A recent product contains insulin that can be administered using a nasal spray. The spray is inhaled and the insulin is taken up through the lungs. shows the concentration of insulin in the blood plasma in the 480 minutes after injecting or inhaling insulin. In both cases, the insulin was of the same type, obtained from genetically engineered Escherichia coli. insulin concentration in blood plasma / arbitrary units time after administration / minutes × × × × × × × × × × × × × × × × × inhaled insulin injected insulin shows the concentration of glucose in the blood plasma in the 480 minutes after injecting or inhaling insulin. glucose concentration in blood plasma / arbitrary units time after administration / minutes × × × × × × × × × × inhaled insulin injected insulin × Compare the results for injected insulin and inhaled insulin shown in . With reference to , explain the differences in the blood glucose levels after injecting or inhaling insulin shown in . With reference to Figs. 4.2 and 4.3, suggest one advantage and one disadvantage of inhaling insulin rather than injecting it. advantage disadvantage
9700_w10_qp_42
THEORY
2010
Paper 4, Variant 2
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Table 7.1 shows the effect of several events on the blood concentration of glucose, insulin and glucagon in a healthy person. Complete the table using the words increase, decrease or no effect. The first row has been done for you. Table 7.1 initial effect of event on blood concentration of event glucose insulin glucagon meal containing sucrose increase increase decrease meal containing only protein fasting exercising meal containing starch The concentration of glucose in the blood is controlled by the hormones insulin and glucagon. Describe the part played by glucagon in the control of glucose in the blood.
9700_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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Many women use knowledge of their menstrual cycle as a family planning method, avoiding sexual intercourse during the part of the cycle when it is possible for fertilisation to occur. This part of the cycle is known as the fertile window. In women with regular, 28-day menstrual cycles, ovulation is likely to take place on day 14. Most guidelines state that the fertile window lasts from day 10 to day 17 of the menstrual cycle. Explain why the fertile window begins several days before ovulation takes place. shows how basal body temperature, and the concentration of luteinising hormone, LH, varied during one menstrual cycle of a woman. Basal body temperature is the temperature of the body just after waking in the morning. 36.8 36.7 36.6 basal body temperature / °C 36.5 36.4 36.3 11 13 day of menstrual cycle concentration of LH LH 23 25 LH body temperature On , sketch a curve to show the changes in the concentration of progesterone in the blood during this menstrual cycle. The follicular phase of the menstrual cycle begins when menstruation starts, and ends when ovulation takes place. With reference to , suggest when the follicular phase began and ended during this menstrual cycle. began …………………………… ended …………………………… Three methods that a woman can use for determining her fertile window are: method 1 using the date at which each menstruation begins to predict when ovulation will occur method 2 using disposable urine dip sticks to measure the amount of LH breakdown products in urine (the more LH in the blood, the more breakdown products are present in urine) method 3 wearing an electronic device in the armpit that continuously measures body temperature. Suggest why using method 1 alone is not likely to be a very reliable method of avoiding conception. Explain how method 2 could be used to avoid conception. Suggest why method 3 is likely to be a better predictor of ovulation than measuring basal temperature with a thermometer each day. A study was carried out into the timing of the fertile window. The study involved 221 women who were trying to get pregnant. Urine samples from each woman were tested for LH breakdown products every day for several months. The women recorded the days on which they had sexual intercourse, and also the days on which menstruation began. 136 of the women became pregnant during the study. The results were used to calculate the probability of a woman being in the fertile window on each day of her cycle. The results for women with regular 28-day cycles are shown in . 0.2 0.4 0.6 day of menstrual cycle probability of being in fertile window Discuss what these results suggest about the guidelines that the fertile window lasts from day 10 to day 17 of the menstrual cycle.
9700_w13_qp_43
THEORY
2013
Paper 4, Variant 3
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Questions Discovered
95