Unit 4 - D Cell Membranes and Transport

AS LEVEL
B I O LO GY

,4 Cell membranes and transport.............................3

4.1 Fluid mosaic membranes ..............................................3
Phospholipids ..............................................................3
Structure of membranes ...............................................4

Cell signaling ..............................................................8
4.2 Movement of substances into and out of cells ...............11
Movement of substances into and out of cells...............12

, 4 CELL MEMBRAN
AND TRANSPOR
The fluid mosaic model introduced in 1972 describes the way in which biolo
are arranged to form cell membranes. The model has stood the test of time
visualize membrane structure and continues to be modified as understandin
the ways in which substances cross membranes, how cells interact and how
to signals. The model also provides the basis for our understanding of pass
movement between cells and their surroundings, cell to cell interactions and
cell signaling.


Investigating the effects of different factors on diffusion, osmosis and memb
permeability involves an understanding of the properties of phospholipids a
covered in the section on Biological molecules.


Candidates will be expected to use the knowledge gained in this section to
in familiar and unfamiliar contexts.



4 .1 F L U I D M O S A I C
MEMBRANES
The structure of cell surface membranes allows movement of substances bet
their surroundings and allows cells to communicate with each other by cell


LEARNING OUTCOMES

C ANDIDATES SHOULD BE ABLE TO:

A. describe and explain the fluid mosaic model of membrane structure, inc
outline of the roles of phospholipids, cholesterol, glycolipids, proteins a