Question 19M.3.SL.TZ1.b
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.SL.TZ1.b |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Explain | Question number | b | Adapted from | N/A |
Membrane structure can be investigated using a technique known as freeze fracture.
Cells are frozen and then split. Fracturing often occurs between the two phospholipid layers of membranes in the cell. An electron micrograph of such a fractured membrane is shown.
[Source: © Science Photo Library]
Explain how electron micrographs such as this helped support the fluid-mosaic model of membrane structure.
[2]
a. the fluid-mosaic proposed two layers of protein on either side of a lipid bilayer ✔ OWTTE
b. micrographs illustrate proteins in and/or crossing the membrane ✔
Descriptions of protein layers either side of the phospholipid bilayer in the Davson-Danielli model were unclear. Embedded or integral proteins were frequently stated for the second marking point.
