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Date May 2019 Marks available 2 Reference code 19M.3.SL.TZ2.17
Level Standard level Paper Paper 3 Time zone Time zone 2
Command term Compare and contrast Question number 17 Adapted from N/A

Question

The diagram shows metabolic pathways for lactate in humans.

[Source: © International Baccalaureate Organization 2019]

State the name of the blood vessel through which lactate from muscles reaches the liver

[1]
a.

Compare and contrast the possible metabolic pathways for lactate in hepatocytes and in mitochondria-rich tissue.

[2]
b.

List two functions of hepatocytes other than regulating lactate levels in the blood.

1.

2.

 

[2]
c.

Markscheme

hepatic artery ✔

a.

a. both produce pyruvate «from lactate»
OR
both produce CO2 and H2O «via acetyl CoA» ✔

b. hepatocytes produce glucose from lactate but mitochondria-rich cells cannot ✔

OWTTE – eg: “only hepatocytes produce glucose” would be acceptable.

b.

a. detoxification ✔

b. production/secretion of bile ✔

c. conversion of cholesterol to bile salts ✔

d. production of plasma proteins ✔

e. nutrient storage ✔

f. glucose regulation «in blood» ✔

g. other function «eg deamination/transamination, conversion of ammonia to urea» ✔

Only two functions are required.

If more than two functions are given, mark only the first two listed.

c.

Examiners report

The data showed possible metabolic pathways for lactate in humans. In (a) many candidates wrongly answered the hepatic portal vein.

a.

Part (b) and (c) were well answered, the main error was confusing the hepatocytes with the Kupffer cells.

b.

Part (b) and (c) were well answered, the main error was confusing the hepatocytes with the Kupffer cells.

c.

Syllabus sections

Option D: Human physiology » Option D: Human physiology (Core topics) » D.3 Functions of the liver
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Option D: Human physiology » Option D: Human physiology (Core topics)
Option D: Human physiology

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