#27 Summary of Cell membrane

1 The basic structure of a membrane is a 7 nm thick phospholipid bilayer with protein molecules
spanning the bilayer or within one or other layer. Phospholipids and some proteins move within the
layers. Hence the structure is described as a fluid mosaic – the scattered protein molecules resemble pieces of a mosaic.

# 26 Surface area to volume ratios, Investigating diffusion

As the radius of a cell ↑ from 1x to 3x (left),
the surface area ↑ from 1x to 9x,
and the volume ↑ from 1x to 27x.
Source: Nature Education 

As a cell increases in size, there is less surface area in proportion to its volume. 

Relatively there is less surface area of cell mebrane over which inffusion can coccur. 

# 25 Passive and active transport across cell membranes

Substances can enter or leave a cell in 2 ways:

1) Passive

a) Simple Diffusion
b) Facilitated Diffusion
c) Osmosis (water only)

2) Active

a) Molecules
b) Particles

#24 Cell membranes - Fluid Mosaic Model of the plasma menbrane

The fluid-mosaic model describes the plasma membrane that surrounds animal cell. The membrane has 2 layers of phospholipids (fats with phosphorous attached), which at body temperature are like vegetable oil (fluid).

#23.2 Cell membranes and transport - Syllabus 2016 - 2018

4.1 Fluid mosaic membranes 
4.2 Movement of substances into and out of cells

#23.1 Cell membranes and transport - Syllabus 2015

• Fluid mosaic model of membrane structure
• Movement of substances into and out of cells