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Date May 2021 Marks available 1 Reference code 21M.1.SL.TZ1.3
Level Standard level Paper Paper 1 Time zone Time zone 1
Command term Question number 3 Adapted from N/A

Question

The Davson–Danielli model of membrane structure proposed that membranes were composed of a phospholipid bilayer that lies between two layers of globular proteins, as shown in this diagram.

[Source: Cornell, B. 2016. https://ib.bioninja.com.au/standard-level/topic-1-cell-biology/13-membrane-structure/membrane-models.html]

 

What evidence supported this model?

A. An electron micrograph that showed two dark lines with a lighter band in between

B. Freeze-fracture electron microscopy

C. Evidence that all membranes are identical

D. The hydrophobic regions of protein would be in contact with water

Markscheme

A

Examiners report

This question was based on the second Skill in 1.3 (Membrane Structure). As part of a study of models in science and how they may be falsified, students are expected to understand that the appearance of membranes in electron micrographs led to the Davson-Danielli model, with a central layer of phospholipid coated on either side by protein. By understanding the original plausibility of this model, students should better understand that some currently accepted models may eventually be proved to be false and that challenging accepted views is an important part of the nature of science.

Syllabus sections

Core » Topic 1: Cell biology » 1.3 Membrane structure
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