Where urea comes from — questions

1. state

Supplement. What does the liver do with the amino acids that the body needs?

Circle one answer.

• It joins them together to make proteins.
• It sends them to the kidneys to excrete.
• It stores them until the body needs them.
• It turns every one of them into urea.

Nudge (only if you are stuck): What are amino acids the building blocks of?

2. state

Supplement. In which organ is urea made?

Circle one answer.

• The small intestine.
• The kidneys.
• The liver.
• The bladder.

Nudge (only if you are stuck): The kidneys remove urea. Which organ makes it?

3. define

Supplement. What is deamination?

Circle one answer.

• Removing urea from the blood in the kidneys to form the urine.
• Joining amino acids together in the liver to form new proteins.
• Removing the nitrogen-containing part of amino acids to form urea.
• Breaking down proteins in the gut to form many amino acids.

Nudge (only if you are stuck): Which organ, and which part of the amino acid?

4. describe

Supplement. Put these events in order, for an amino acid that the body does not need.

Write the number of each step in order.

1. Its nitrogen-containing part is removed.
2. The blood carries the urea to the kidneys.
3. The urea leaves the body in urine.
4. Urea is formed.
5. An excess amino acid arrives in the liver.

• First: ______
• Second: ______
• Third: ______
• Fourth: ______
• Last: ______

Nudge (only if you are stuck): Where is it deaminated, and where is the urea excreted?

5. explain

Supplement. Why must urea be excreted?

Circle one answer.

• It is toxic: a build-up in the blood harms the cells.
• It is a fuel: a build-up makes cells respire too fast.
• It is solid: a build-up blocks the blood vessels.
• It is a protein: a build-up thickens the blood plasma.

Nudge (only if you are stuck): What would it do if it built up in the blood?

6. define

Supplement. Match each process to its meaning.

Write the number of the matching option.

1. breaking proteins into amino acids in the gut
2. making amino acids into the body's proteins
3. removing the nitrogen-containing part of an amino acid
4. removing waste of metabolism from the body

• Assimilation: ______
• Deamination: ______
• Excretion: ______
• Digestion: ______

Nudge (only if you are stuck): Two of them happen in the liver.

7. calculate

Supplement. A growing teenager eats 85 g of protein in a day. Their body builds the amino acids from 15 g of it into new proteins. The rest are excess amino acids, which are deaminated. Each gram of protein deaminated gives about 0.34 g of urea. Calculate the mass of urea made in the day.

Mass of urea: ______________ unit ________

Nudge (only if you are stuck): Only the excess amino acids are deaminated. How much protein is that?

8. predict / explain

Supplement. A healthy woman gives one of her kidneys to her brother. A month later her remaining kidney is working well. Predict the concentration of urea in her blood, compared with before she gave the kidney, and explain why this matters.

Nudge (only if you are stuck): Does one healthy kidney still remove urea from the blood?

9. identify

Supplement. Urea contains four elements: carbon, hydrogen, oxygen and nitrogen. Which substance does the liver use to make urea, and why?

Circle one answer.

• Glucose, because it contains carbon, as urea does.
• Fatty acids, because they contain hydrogen, as urea does.
• Glycerol, because it contains oxygen, as urea does.
• Amino acids, because they contain nitrogen, as urea does.

Nudge (only if you are stuck): Which element does urea contain, and which food molecule carries it?

10. describe / explain

Supplement. The table shows the mass of urea one adult excreted on five days with different amounts of protein in their food. One result does not fit the pattern. (a) Identify the anomalous result, and describe the pattern shown by the other four. (b) Explain the pattern.

(a) Anomalous result and pattern

(b) Explanation

Nudge (only if you are stuck): Look down both columns together: which row breaks the trend of the rest?

11. predict / explain

Supplement. After a high-protein meal, blood arrives at the liver from the gut, and leaves the liver in the hepatic vein. Compare the blood leaving the liver with the blood arriving from the gut: (a) which has more amino acids, and (b) which has more urea? Explain.

(a) More amino acids

(b) More urea

Nudge (only if you are stuck): What does the liver take out, and what does it add?

12. explain

Supplement. A man has kidney disease: his kidneys still work, but they remove urea from his blood much more slowly than healthy kidneys do. His doctor advises him to eat less protein. Explain how this helps him.

Nudge (only if you are stuck): Where does urea come from, and what decides how much of it is made?