Factors Affecting the Cell Membrane

This lesson covers:

  1. How temperature affects membrane structure and permeability
  2. How solvents affect membrane structure and permeability

Different factors affect the permeability of membranes

Cell membranes control the movement of substances into and out of cells (or organelles). However, changes to the structure of cell membranes can increase their permeability, allowing more substances to pass through.


You need to be able to describe and explain how the following two factors affect the permeability of membranes: 

  1. Temperature
  2. Solvents

Temperature

Changes in temperature affect the movement of phospholipids and the structure of proteins in the cell membrane.

Graph showing membrane permeability against temperature with marked points at below 0°C, 0-40°C, and above 40°C.

How temperature affects cell membranes:

  1. At low temperatures (below 0°C) - Phospholipids do not have much kinetic energy. They are packed closely together to form a rigid cell membrane, decreasing the permeability of the membrane. 
  2. At medium temperatures (0 - 40°C) - As temperature increases, phospholipids have more kinetic energy so they move faster and aren't packed as closely together. This increases the permeability of the membrane. 
  3. At high temperatures (above 40°C) - The phospholipid bilayer breaks down. Channel and carrier proteins denature, meaning they cannot control what enters or leaves the cell. These effects increase the permeability of the membrane.

Solvents 

Solvents are liquids that have the ability to dissolve substances. 


When cells are placed in a solvent such as ethanol, the phospholipids dissolve, causing the membrane to become more fluid. This disrupts the structure of the cell membrane to make it more permeable. 


Increasing the concentration of the solvent will further increase the permeability of the cell membrane.