Amoebas (singular amoeba) are free-living, single-celled eukaryotes that live in freshwater ponds and lakes. They carry out osmoregulation using an organelle called a contractile vacuole, shown in the image below.
Explain why amoebas need to carry out osmoregulation.
The graph below shows what happens to various components of the glomerular filtrate as they move through the different regions of an individual’s nephron.
Describe and explain the shape of the curve for glucose concentration.
Explain the shapes of the curves for sodium ions and water in the graph in part a) as they travel through the first half of region 2 of the nephron. Note that region 2 in this graph is the loop of Henle.
The image below shows cells lining the collecting duct. ADH released from the pituitary gland binds to the receptor proteins on the collecting duct cell surface membranes. This triggers vesicles containing aquaporins to bind with the plasma membrane next to the lumen. Note that aquaporins are channel proteins that enable the movement of water molecules.
Explain how ADH increases the movement of water from the lumen of the collecting duct into the blood.
The table below shows the maximum urine solute concentrations that can be achieved in different species of mammal. Seawater has been included for comparison.
Solute concentration / mEq L-1
Urine:blood plasma osmolarity ratio
Human urine
460
Brown rat urine
600
8:1
Kangaroo rat urine
1200
14:1
Seawater
600
N/A
Humans have a blood plasma concentration of roughly 120 mEq L-1.
Calculate the urine:blood plasma osmolarity ratio in humans.
A researcher wanted to investigate kangaroo rat kidneys. They fed the kangaroo rats on soybeans for several days to increase their thirst (kangaroo rats normally get all their water from their food), and then either gave the rats access to fresh water, seawater, or no water for the following 16 days, using weight over the experimental period as a measure of rat health. The results are shown in the graph below.
Suggest, with a reason, one possible conclusion about the capabilities of kangaroo rat kidneys that can be drawn from the graph above. Note that humans cannot drink seawater without becoming severely dehydrated.
