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Date	May 2019	Marks available	1	Reference code	19M.1.HL.TZ1.3
Level	Higher level	Paper	Paper 1	Time zone	Time zone 1
Command term	Identify	Question number	3	Adapted from	N/A

Question

Which is an essential feature of the Davson–Danielli model of membrane structure?

A. A phospholipid monolayer with intrinsic and extrinsic proteins

B. A layer of protein sandwiched between two layers of lipid

C. A phospholipid bilayer with intrinsic and extrinsic proteins

D. A layer of lipid sandwiched between two layers of protein

Markscheme

Examiners report

This also proved to be too difficult, with scarcely more candidates answering correctly than the guess-level of 25%. The terms use of the terms ‘intrinsic’ and ‘extrinsic’ was unfortunate because ‘integral’ and ‘peripheral’ have been preferred for many years in IB Biology. Perhaps candidates thought that these were the two layers of protein on the membrane surface with the Davson-Danielli model which would lead incorrectly to answer C. Despite this, candidates should have been able to choose answer D, which is an unambiguous description of the Davson-Danielli model. Stronger candidates did tend to choose this answer, as the discrimination index was quite high.

Syllabus sections

Core » Topic 1: Cell biology » 1.3 Membrane structure

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