14. Homeostasis
A section of Biology, 9700
Listing 10 of 131 questions
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. 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. The domestic dog, Canis lupus familiaris, is a mammal. A dog may develop a condition called Cushing’s disease, which is a result of too much cortisol being secreted by the adrenal glands. The most common cause of this is an increased secretion of ACTH because of a tumour in the anterior pituitary gland. Explain how a tumour develops. 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.
9700_s20_qp_41
THEORY
2020
Paper 4, Variant 1
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The hormone FSH (follicle stimulating hormone) plays important roles in the reproductive cycles of mammals. State the precise site of secretion of FSH. Certain cells in the ovaries and testes have receptors for FSH in their cell surface membranes. FSH can bind with these receptors, which triggers the cells to respond to the hormone. Mice were genetically modified so that they lacked functioning alleles of the gene that codes for the production of FSH receptors. Female mice without FSH receptors were sterile. They were found to have normal primary and secondary follicles in their ovaries, but no Graafian follicles or corpora lutea. Explain these observations. Spermatozoa were collected from male mice with and without FSH receptors. The mean number of spermatozoa per mouse was estimated. The percentage of spermatozoa that could swim actively was calculated. Table 5.1 shows the results. Table 5.1 male mice with FSH receptors male mice without FSH receptors mean number of spermatozoa per mouse 5.6 × 106 3.6 × 106 percentage of spermatozoa that could swim actively Discuss what these results suggest about the role of FSH in the development of spermatozoa in male mice.
9700_s14_qp_42
THEORY
2014
Paper 4, Variant 2
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The passage outlines the endocrine system. Complete the passage by using the most appropriate scientific terms. The endocrine system consists of tissues and , which secrete hormones such as insulin, glucagon and antidiuretic hormone (ADH). Glucagon only affects target cells that have complementary receptors, which are located on the . Glucagon binds to these receptors and this leads to the production of a , which transfers the signal throughout the cytoplasm. The target cells for insulin are in the liver, and adipose tissue. The target cells for ADH are those of the distal convoluted tubule and the of the kidney nephron. These hormones are involved in , which is the maintenance of a constant internal environment. The blood glucose concentration of a person was measured at regular intervals after the ingestion of a meal rich in glucose. shows the results of this investigation. blood glucose concentration / mmol dm–3 time / h glucose-rich meal ingested set point A B Explain how the blood glucose concentration is reduced during phase A of the curve. Suggest why the blood glucose concentration increases again during phase B.
9700_s23_qp_42
THEORY
2023
Paper 4, Variant 2
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Erythropoietin, also known as EPO, is a large glycoprotein synthesised by specialised cells in the kidney. These cells are very sensitive to changes in oxygen concentration in the blood passing through the kidney and respond to a low oxygen concentration by increasing the synthesis of EPO. EPO acts at the surface of particular target cells, such as cells in the bone marrow. These bone marrow cells are stimulated to produce red blood cells. A low oxygen concentration also leads to an increase in the quantity of mRNA in the specialised cells in the kidney. Suggest and explain why there is this increase in the quantity of mRNA. EPO is stored in secretory vesicles before being released from the specialised kidney cells. Outline how EPO is released from the cells. All cells of the body are exposed to circulating blood plasma containing EPO, but only particular target cells respond. Suggest and explain how EPO acts on target cells and why other cells are not affected. EPO cannot pass through the cell surface membrane to enter the bone marrow cells. Suggest one reason why this is so. Red blood cells originate from undifferentiated cells in the bone marrow that are capable of continuous mitotic cell division. State the name of this type of undifferentiated cell. As part of an investigation into the body’s response to EPO, a group of healthy young men were given injections of EPO every day for four weeks. The haemoglobin (Hb) concentration for each subject was measured at the start of the investigation and then at intervals of one week for the next ten weeks. The first measurement was taken two weeks before the first EPO injection was given. shows the mean results for the subjects. time / weeks mean Hb concentration / g per kg body mass first EPO injection final EPO injection Describe the results shown in and suggest explanations for these results. The concentration of EPO in the blood plasma of a person will increase when travelling from sea level to a high altitude. This is in response to the decrease in oxygen partial pressure in the atmosphere. Explain why an increase in EPO blood plasma concentration will be of benefit if the person remains at high altitude.
9700_m16_qp_22
THEORY
2016
Paper 2, Variant 2
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outlines how two hormones, A and B, are involved in the regulation of blood glucose concentration. normal blood glucose concentration endocrine tissue hormone A produced target tissue: liver release of glucose hormone B produced target tissue: liver absorption of glucose fall in blood glucose concentration fall in blood glucose concentration rise in blood glucose concentration rise in blood glucose concentration With reference to , name: the control mechanism that regulates blood glucose concentration hormone A. The enzymes glycogen synthetase and glycogen phosphorylase are both involved in the formation and breakdown of glycogen in the liver. shows the activity of the two enzymes in the liver after consumption of a glucose meal. time after glucose meal / s activity of enzyme / arbitrary units glycogen phosphorylase glycogen synthetase Describe and suggest an explanation for the changes in the activity of the enzymes glycogen synthetase and glycogen phosphorylase.
9700_m16_qp_42
THEORY
2016
Paper 4, Variant 2
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The hormone glucagon is an example of a cell signalling molecule. Table 2.1 lists the main events that occur when the blood glucose concentration decreases below the set point. The events are not listed in the correct order. Table 2.1 event description of event A adenylyl cyclase enzyme is activated B cyclic AMP activates an enzyme cascade C glycogen stored in liver cells is broken down to glucose D blood glucose concentration increases E glucagon is secreted by α cells in the pancreas F conformational change to glucagon receptor causes G-protein activation G active adenylyl cyclase acts on ATP to produce second messenger H glucagon signal is amplified I glucose diffuses out of liver cells through GLUT transporter proteins J glucagon binds to receptors in the cell surface membranes of liver cells K cyclic AMP is formed An investigation was carried out to measure the rate at which glucose is provided for respiration from three different sources of glucose: • a meal • glycogenolysis – the breakdown of glycogen • gluconeogenesis – production of glucose from non-carbohydrate molecules. After a person ate a meal, the rates at which glucose was provided for respiration from the three different sources were measured at regular intervals over a 24-hour period. During this period, no food was eaten. shows the results of this investigation. rate at which glucose is provided for respiration / g h–1 time after meal / h from meal from glycogenolysis from gluconeogenesis State the time after the meal when the rate at which glucose was provided from the meal for respiration was the same as the rate at which glucose was provided from glycogenolysis for respiration. State the first time after the meal when all of the glucose for respiration was provided by gluconeogenesis. Name the homeostatic mechanism by which blood glucose concentration is maintained at a set point. In humans, carbohydrates such as glucose are not the only respiratory substrates. Name two non-carbohydrate respiratory substrates in humans.
9700_m19_qp_42
THEORY
2019
Paper 4, Variant 2
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Questions Discovered
131