14. Homeostasis
A section of Biology, 9700
Listing 10 of 131 questions
The human kidneys process 1200 cm3 of blood every minute. This 1200 cm3 of blood contains 700 cm3 of plasma. As blood passes through the glomeruli of the kidneys, 125 cm3 of fluid passes into the renal capsules (Bowman’s capsules). This fluid is called the glomerular filtrate and is produced by a process called ultrafiltration. Calculate the percentage of plasma that passes into the renal capsules. Show your working and give your answer to one decimal place. answer % Explain how the structures of the glomerular capillaries and the podocytes are adapted for ultrafiltration. glomerular capillaries podocytes The glomerular filtrate then passes through the proximal convoluted tubule. is a transverse section through part of the proximal convoluted tubule. X Name the structures labelled X. Explain why the epithelial cells of the proximal convoluted tubule have many mitochondria in them. Of the 125 cm3 of glomerular filtrate that enters the renal capsules each minute, only 45 cm3 reaches the loops of Henlé. Name two substances that are reabsorbed into the blood from the proximal convoluted tubule, apart from water.
9700_s13_qp_42
THEORY
2013
Paper 4, Variant 2
View
is a diagram of a Bowman’s capsule of a nephron from a mammalian kidney. On , use label lines and letters to label: E – the efferent arteriole G – the glomerulus P – the region of podocyte cells. Describe how the structure of the epithelial cells of the proximal convoluted tubule is adapted to carry out selective reabsorption. Complete the following sentences about osmoregulation. In mammals, the water potential of the blood is constantly monitored by in the hypothalamus of the brain. When the water potential of the blood decreases, the production of a hormone called in the cells of the hypothalamus increases. This hormone is released into the blood via the This causes the kidneys to retain more water until the water potential of the blood returns to the set point. This is an example of a mechanism.
9700_s17_qp_42
THEORY
2017
Paper 4, Variant 2
View
is a photomicrograph of part of the cortex of a kidney. On , use label lines and letters to label: G – the glomerulus L – the lumen of the Bowman’s capsule. During ultrafiltration, components of blood in the glomerulus with a relative molecular mass greater than 68 000 are prevented from passing into the Bowman’s capsule. Name the structure that acts as this filtration barrier. The glomerular filtration rate (GFR) is the rate of flow of filtered fluid through the kidneys per unit time. The afferent arterioles supply blood to the glomerulus of each nephron within the kidney and the efferent arterioles take blood away from each glomerulus. The lumen diameters of the afferent and efferent arterioles have a large effect on the GFR. Normally the lumen diameters of the afferent and efferent arterioles are different, but they can change to increase or decrease the normal GFR in response to changing conditions. Complete Table 5.1 to indicate whether the GFR is normal, increased, or decreased for each combination of arteriole diameters shown. The first row has been completed for you. Table 5.1 afferent arteriole lumen diameter efferent arteriole lumen diameter GFR normal normal normal decreased normal normal increased After leaving the Bowman’s capsule, the glomerular filtrate passes through the proximal convoluted tubule, where selective reabsorption occurs. Describe and explain how all of the glucose in the glomerular filtrate is reabsorbed back into the blood. State and explain three features of a proximal convoluted tubule cell that adapt it to its function.
9700_s19_qp_42
THEORY
2019
Paper 4, Variant 2
View
Ultrafiltration in the kidney takes place between the glomerulus and the Bowman’s capsule. The afferent blood vessel carrying blood to the glomerulus has a wider lumen than the efferent blood vessel. Explain why the lumen of the afferent blood vessel needs to be wider than the lumen of the efferent blood vessel. is a diagram of part of the glomerulus and Bowman’s capsule. B A blood capillary lumen of Bowman’s capsule Name A and B. A B Describe the roles of A and B in the formation of the glomerular filtrate.
9700_s22_qp_42
THEORY
2022
Paper 4, Variant 2
View
is a photomicrograph of a section through a Bowman’s capsule and a glomerulus. On , use label lines and letters to label: F – the location of the glomerular filtrate P – the location of the blood plasma. The glomerular filtration rate (GFR) is the rate at which fluid filters from the blood in the glomerulus into the Bowman’s capsule. shows the mean GFR values for healthy males and females of different age groups. mean GFR / cm3 min–1 age groups / years Key: 20–29 30–39 40–49 50–59 60–69 70–79 80–89 males females Use to calculate the yearly rate of decrease in mean GFR from the 20–29 age group to the 80–89 age group for females. Show your working. Give your answer to one decimal place and include units. answer The age of a person and whether they are male or female can affect GFR. Suggest and explain other factors that can affect GFR. The glomerular filtrate passes from the Bowman’s capsule to the proximal convoluted tubule, where selective reabsorption takes place. Describe the process of selective reabsorption.
9700_s23_qp_42
THEORY
2023
Paper 4, Variant 2
View
shows part of the Bowman’s capsule of a kidney nephron. lumen of capillary not to scale lumen of Bowman’s capsule A B C Name structures A, B and C. A B C Fluid is forced into the Bowman’s capsule by ultrafiltration to form the glomerular filtrate. Describe the role of structure B in ultrafiltration. The main component of the glomerular filtrate formed in the Bowman’s capsule is water. Most of this water is reabsorbed as the filtrate passes along the nephron. • 180 dm3 of water forms part of the glomerular filtrate each day. • 1.4 dm3 of water leaves the body in urine each day. Calculate the percentage of water in the glomerular filtrate that is reabsorbed as the glomerular filtrate passes along the nephron. Show your working and give your answer to one decimal place. answer % Describe how the action of antidiuretic hormone (ADH) on the cells of the collecting duct leads to the reabsorption of water in the glomerular filtrate.
9700_s23_qp_43
THEORY
2023
Paper 4, Variant 3
View
shows a section through part of the cortex of a kidney. On , draw label lines and use the letters G and R to identify : • a glomerulus with the letter G. • a renal capsule with the letter R. State the name of the hormone that is involved in the control of the water potential of the blood. Table 7.1 shows the concentration of some compounds in the fluids of a glomerulus, a renal capsule and a collecting duct of the kidney. Table 7.1 compound concentration / g 100 cm–3 blood plasma entering glomerulus filtrate in renal capsule urine in collecting duct water proteins 8.0 0.0 0.0 glucose 0.1 0.1 0.0 urea 0.03 0.03 2.0 With reference to Table 7.1, explain why proteins occur in the blood entering the glomerulus but not in the filtrate in the renal capsule explain why there is glucose present in the filtrate but not in the urine explain the difference in the concentration of urea between the filtrate and urine.
9700_w08_qp_4
THEORY
2008
Paper 4, Variant 0
View
Questions Discovered
131