Factors that Influence Diffusion (Cambridge O Level Biology)

• There are four key factors that influence diffusion of particles
  • Surface area to volume ratio
  • Distance
  • Temperature
  • Concentration gradient

Surface area to volume ratio

• The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface
• Many cells which are adapted for diffusion have increased surface area in some way - e.g. root hair cells in plants (which absorb water and mineral ions) and cells lining the ileum in animals (which absorb the products of digestion)

Diffusion and surface area to volume ratio diagram

Cell adaptations for diffusion 

The highly folded surface of the small intestine increases its surface area

Distance

• The shorter the distance molecules have to travel, the faster diffusion will occur
• This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible

Temperature

• The higher the temperature, the faster molecules move
• This is because they have more kinetic energy
• This results in more collisions against the cell membrane and therefore a faster rate of movement across them

Concentration Gradient

• The greater the difference in concentration on either side of the membrane, the faster movement across it will occur
• This is because on the side with the higher concentration, more random collisions against the membrane will occur