Ultrafiltration & selective reabsorption

The diagram shows a nephron from a human kidney.

Name the structures labelled A, B, C and D.

The nephron produces urine that flows out of tube A to the bladder. Explain how changes in the composition of this liquid are brought about when a person is dehydrated (short of water).

Students carried out an experiment about kidney function. Their teacher provided them with three samples of artificial urine.

• one sample contained the same composition as urine from a person with normal kidneys

• one sample contained the same composition as urine from a person with diabetes, who is unable to produce insulin

• one sample contained the same composition as urine from a person with high blood pressure

The students tested the samples for glucose and for protein. The table shows their results.

High blood pressure occurs when the heart has to pump very hard to force blood through narrow arteries.

Use information from the table and your own knowledge to explain which sample could be from a person with high blood pressure.

Use information from the table and your own knowledge to explain which sample could be from a person with diabetes.

Describe the test for glucose.

Suggest why the teacher uses artificial urine rather than real urine in this experiment.

The diagram shows a kidney nephron with parts labelled A, B and C.

The table lists events that take place in the nephron. Complete the table by giving the letter of the part where each event takes place.

The photograph shows a flower called a dandelion.

If a person picks this flower and then licks their fingers, they will want to urinate. This is because the plant produces a chemical called a diuretic that affects the regulation of the water content of the blood. Suggest how this diuretic causes more urine to be produced.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Glucose control Many years ago some scientists wanted to find out more about the role of the pancreas in digestion. They used surgery to remove the pancreas from dogs to see what would happen. During this investigation a laboratory assistant noticed that flies collected around the dogs’ urine. This urine was later found to contain large amounts of glucose. Urine from dogs with a pancreas does not contain glucose. Another scientist used string to tie a knot around the pancreatic duct of rabbits, which closed the duct. This meant that no pancreatic enzymes could reach the small intestine. It was noticed that when this was done, the cells in the pancreas that made enzymes died, but no glucose appeared in the rabbit urine. Other scientists made pancreas extract by crushing up a pancreas in water. They injected this extract into dogs that had their pancreas removed. They found that the blood glucose level in these dogs was much reduced. These investigations and observations suggest that the pancreas has two different functions. Some of the cells produce enzymes needed for digestion. Other parts of the pancreas are not involved in digestion but are important in controlling blood glucose levels. We now know that pancreas extract contains two hormones involved with the regulation of blood glucose levels – insulin and glucagon. High blood glucose levels are detected by the pancreas. This stimulates the pancreas to release insulin. The role of insulin is to lower blood glucose levels. The insulin is released from specialised cells directly into the blood. The insulin travels in the blood to target cells that are in the liver and in large muscles. Insulin causes these cells to absorb glucose and use it to make an insoluble storage carbohydrate called glycogen. The second hormone called glucagon is released by different cells in the pancreas when the blood glucose level falls too low. Glucagon causes liver and muscle cells to change glycogen into soluble glucose.

Explain what is meant by the term digestion (line 2).

Explain why dogs that had their pancreas removed produced urine that contained glucose (lines 4 and 5).

Name two enzymes produced by cells in the pancreas (lines 8 and 9).

Suggest why rabbits that have had their pancreatic duct tied can still regulate their blood glucose levels (lines 10 and 11).

The scientists who injected pancreas extract into dogs should have carried out a control experiment (line 13). Explain the control experiment they should have carried out.

Name the blood vessel that transports hormones into the liver (line 24).

Suggest one advantage of storing glycogen in cells rather than storing glucose in cells (lines 25 and 26).

A number of different substances and structures are involved in the control of blood glucose.

Describe the stimulus.

Name the structure that acts as a receptor.

Name a structure that acts as an effector.

Describe the response.

The diagram shows a section through a rat. Some of the rat’s organs have been labelled.

What is meant by the term organ ?

Name the organ labelled in the diagram that is part of the circulation system.

Name three other systems shown in the diagram.

Name a system that is not shown in the diagram.

The table lists several processes that take place in the organs of a rat. Complete the table by naming the correct organ for each process.

The photograph shows an Arabian oryx.

Arabian oryx live in the desert where there is no free-standing water. Most of their habitat is sand. Plants, such as grass and small trees, cover only a small area. Oryx feed mainly on grass. Summers are hot. Daytime temperatures can be as high as 41 °C and temperatures at night only fall to 24 °C. Oryx are less active in summer than in winter. In summer, they reduce their energy use by changing their behaviour and body processes.

Suggest why oryx are less active in summer than in winter.

In summer, oryx rest under trees during the day and feed at night. Suggest why they do this.

Suggest where the oryx get their water from in the absence of free-standing water.

Oryx and humans can control water loss by making their urine very concentrated. Describe how this is done.

The diagram shows some of the blood vessels and a nephron in the human kidney. The numbers represent the concentration of glucose at various places in the blood vessels and in the nephron, in arbitrary units.

Explain how the structure of the blood vessels entering and leaving the glomerulus help to move glucose into the Bowman’s capsule.

What type of blood vessels are found in the glomerulus?

Describe how glucose is reabsorbed from the nephron back into the blood.

Suggest why glucose needs to be returned to the blood.