The role of diffusion in and within cells

 

What is diffusion?

In scientific terms, DIFFUSION is the MOVEMENT OF PARTICLES from a region of HIGH CONCENTRATION to a region of LOW CONCENTRATION.

Diffusion is a passive process, it does  not require any energy for it to happen.

 

The easiest kind of diffusion is when different gases diffuse through each other.  For example, it happens when a perfume smell spreads through out the air in an enclosed area.  Likewise, diffusion of gases also take place in the leaves.

 

 

Cell Membrane and Diffusion

Diffusion across cell membranes is just like simple diffusion in air, PARTICLES flow through cell membrane from a region of HIGH CONCENTRATION (many of them) to a region of LOW CONCENTRATION (only a few of them).  This is constantly happening in your lungs.

 

 

Cell membranes hold everything inside a living cell.  However, for a cell to function properly they let stuff in and out as well.  These membranes are quite choosey.  They only allow very small molecules to diffuse through them - stuff like glucose and/or amino acids.

Large molecules like PROTEINS and/or STARCH can't diffuse through cell membranes.

 

Exchange of gases in the Lungs

 

Breathing is a gas exchange mechanism.  Your Lungs help to do just that!  They contain millions of  tiny air pockets called ALVEOLI (air sacs)  which are adapted to maximise the diffusion of carbon dioxide and oxygen (see diagram below).  Alveoli  are good at gas exchange because they have:

• a large surface area.  If all the air sacs were flattened out, they would cover an area of 100m2
• moist surface which speed up diffusion.
• very thin walls which makes diffusion quicker.
• lots of blood capillaries to carry the gasses.
• the blood capillaries help the diffusion O₂ and CO₂ as their walls are only one cell thick.

In the alveolus (single air sac) oxygen passes from a high concentration (loads of oxygen) through the thin wall into the blood capillary where there is a low concentration (very little oxygen) .  This is called diffusion, because oxygen is moving from high concentration to low concentration.  When blood returns to lungs it has high concentration of carbon dioxide, so CO₂ diffuses out of the blood into the alveolus.

 

Active Transport Uptake

 

Summary:

 

• Particles move from high to low concentrations by diffusion.
• Diffusion is a natural process that does not need energy.
• Oxygen, carbon dioxide and glucose diffuse in and out of cells.