14.1. Homeostasis in mammals
A subsection of Biology, 9700, through 14. Homeostasis
Listing 10 of 95 questions
Glucagon-like peptide-1 (GLP-1) is a hormone consisting of 31 amino acids. It is secreted by specialised intestinal epithelial cells known as L cells. outlines the secretion of GLP-1 and its effects on the pancreas, brain and stomach. food ingested stomach stomach empties GLP-1 secreted nutrients stimulate L cells in intestine decrease in appetite decrease in glucagon secretion increase in insulin secretion brain inhibition pancreas α cells β cells GLP-1 binds to receptors on cell surface membranes of β cells in the pancreas. These cells secrete insulin. Name the type of membrane component that forms a receptor in the cell surface membrane. State how GLP-1 is transported to the pancreas. GLP-1 inhibits the secretion of glucagon by α cells in the pancreas. Describe two processes in the liver that are stimulated by glucagon. Suggest one reason why GLP-1 causes a decrease in appetite. GLP-1 inhibits the emptying of the stomach. This is an example of negative feedback. Explain what is meant by negative feedback. A transcription factor is involved in the production of GLP-1. An insertion mutation in the gene that codes for the transcription factor can affect the production of GLP-1. Outline the effect of an insertion mutation on the production of GLP-1.
9700_s21_qp_42
THEORY
2021
Paper 4, Variant 2
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Use Hormones are secreted by endocrine glands. Explain what is meant by the term endocrine gland. shows the changes in concentration in the blood of follicle stimulating hormone (FSH) and luteinising hormone (LH) during the first half of the menstrual cycle. days from start of menstrual cycle FSH LH concentration of hormone in blood /arbitrary units With reference to , describe, the changes that take place in the ovary during this time, as a result of the action of FSH the role of LH. Examiner’s Use In preparation for in-vitro fertilisation (IVF), women are injected with FSH. Explain why treatment with FSH is a necessary preparation for IVF. The standard treatment with FSH and clomiphene causes significant side-effects. Clomiphene occupies oestrogen receptors, blocking a negative feedback mechanism. Explain briefly what is meant by negative feedback. Outline the feedback mechanism that is blocked by clomiphene. Recently a so-called ‘mild’ treatment has been introduced in the hope of avoiding the side-effects of the standard treatment. This treatment does not use clomiphene. Instead, an antagonist to LH secretion is used. The days in the first half of the menstrual cycle on which injections of FSH and clomiphene are given in the two treatments are shown by asterisks (*) in . days from start of menstrual cycle * * * * * * * * FSH antagonist to LH secretion * * * * * * * * * * * * * * * * FSH mild treatment standard treatment clomiphene With reference to the concentrations of LH shown in , show, using an asterisk on when the antagonist to LH secretion should first be given. Put your asterisk into the grey area on . Examiner’s Use Suggest why an antagonist to LH secretion forms part of the mild treatment. The average dose of FSH given in the mild treatment is 1300 international units (IU), compared with an average dose of 1800 IU in the standard treatment. This could lead to the mild treatment being less effective. The outcomes of an investigation into the two treatments are shown in Table 5.1. Table 5.1 mild treatment standard treatment mean number of oocytes harvested per treatment cycle 6.7 8.5 mean number of embryos produced per treatment cycle 2.8 3.8 percentage of pregnancies resulting in live birth 43.4 44.7 With reference to Table 5.1, compare the effectiveness of the two treatments. FSH consists of two polypeptide chains which are encoded by genes on different chromosomes. The two genes, together with their promoters, have been inserted into bacteria to produce the hormone used in fertility treatments. Explain briefly why promoters need to be transferred into the recipient bacteria together with the two genes for the FSH polypeptides.
9700_w09_qp_41
THEORY
2009
Paper 4, Variant 1
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Homeostasis in mammals involves negative feedback mechanisms. Outline how a negative feedback mechanism works. is a diagram summarising the role of the nervous and endocrine systems in the control of blood glucose concentration. hypothalamus neurones neurones β cells α cells pancreas insulin glucagon adrenal glands adrenaline decrease in blood glucose concentration increase in blood glucose concentration With reference to , describe the role of the nervous system in the control of blood glucose concentration. If the core temperature of the human body falls, the hypothalamus sends impulses to activate several physiological responses, some of which are listed below. For each one, state how it would help to bring the core temperature back to normal. vasoconstriction shivering increasing secretion of adrenaline
9700_w17_qp_41
THEORY
2017
Paper 4, Variant 1
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Homeostasis in mammals involves negative feedback mechanisms. Outline how a negative feedback mechanism works. is a diagram summarising the role of the nervous and endocrine systems in the control of blood glucose concentration. hypothalamus neurones neurones β cells α cells pancreas insulin glucagon adrenal glands adrenaline decrease in blood glucose concentration increase in blood glucose concentration With reference to , describe the role of the nervous system in the control of blood glucose concentration. If the core temperature of the human body falls, the hypothalamus sends impulses to activate several physiological responses, some of which are listed below. For each one, state how it would help to bring the core temperature back to normal. vasoconstriction shivering increasing secretion of adrenaline
9700_w17_qp_43
THEORY
2017
Paper 4, Variant 3
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The passage below outlines homeostasis. Complete the passage by using the most appropriate scientific terms. Homeostasis, in mammals, is the process of keeping the environment of the body in optimum conditions so that cells can function efficiently. Blood water potential, core temperature and blood glucose concentration are all factors that need to be kept at optimum values or set-point. When a condition deviates from its set-point, a corrective mechanism is triggered. An increase in blood glucose concentration triggers processes to decrease it and vice versa. This corrective mechanism is called . The pancreas is involved in the control of blood glucose concentration. Glucose binds to on the cell surface membrane of pancreatic cells. These are cells, which secrete hormones such as insulin and glucagon. The two hormones have opposite effects on the blood glucose concentration. For example the action of one hormone stimulates the uptake of glucose by cells for respiration and the action of the other hormone stimulates the breakdown of to glucose in the liver.
9700_w22_qp_41
THEORY
2022
Paper 4, Variant 1
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The passage below outlines homeostasis. Complete the passage by using the most appropriate scientific terms. Homeostasis, in mammals, is the process of keeping the environment of the body in optimum conditions so that cells can function efficiently. Blood water potential, core temperature and blood glucose concentration are all factors that need to be kept at optimum values or set-point. When a condition deviates from its set-point, a corrective mechanism is triggered. An increase in blood glucose concentration triggers processes to decrease it and vice versa. This corrective mechanism is called . The pancreas is involved in the control of blood glucose concentration. Glucose binds to on the cell surface membrane of pancreatic cells. These are cells, which secrete hormones such as insulin and glucagon. The two hormones have opposite effects on the blood glucose concentration. For example the action of one hormone stimulates the uptake of glucose by cells for respiration and the action of the other hormone stimulates the breakdown of to glucose in the liver.
9700_w22_qp_43
THEORY
2022
Paper 4, Variant 3
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Questions Discovered
95