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Date May 2019 Marks available 1 Reference code 19M.1.SL.TZ2.10
Level Standard level Paper Paper 1 Time zone Time zone 2
Command term Determine Question number 10 Adapted from N/A

Question

Lactose intolerance occurs when the enzyme, lactase, that digests lactose is not produced after infancy in humans. The incidence of lactose intolerance varies in different racial groups. The graph shows the distribution of lactose intolerance in different human populations.

[Source: © International Baccalaureate Organization 2019]

 

What can be hypothesized from the graph?

A. Native American people produce most lactase after infancy.

B. Most Indian people do not produce lactase after infancy.

C. Lactase is not produced after infancy in most Caucasian people.

D. One quarter of Afro-Caribbean people will probably experience digestive problems when drinking milk.

Markscheme

B

Examiners report

Candidates were expected to choose answer B by eliminating the other answers, which were clearly incorrect. Three quarters of candidates did this and the discrimination index was as high as is expected for a relatively easy question. In fact an allele frequency of 0.25 implies that 56% of adult Indians would not produce lactase, not 75%, but the question asked for a hypothesis rather than the actual percentage in the population. Candidates are not expected to have studied the Hardy-Weinberg equation or know that the allele concerned is autosomal rather than sex-linked, so the task in this question was to choose the most plausible answer and this was certainly B.

Syllabus sections

Core » Topic 2: Molecular biology » 2.5 Enzymes
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