Gas exchange in animals - Edexcel Factors affecting the rate of diffusion
For an organism to function, substances must move into and out of cells. Three processes contribute to this movement 鈥 diffusion, osmosis and active transport.
distance - if the diffusion distance is small, diffusion happens faster because the particles do not have as far to travel
concentration difference (concentration gradient) - diffusion is faster if there is a big difference in the concentration between the area the substance travels from and the area that it is moving to
surface area - the larger the surface area the higher the number of particles that will be able to move in a given time so the faster the rate
Alveoli in the lungs, fish gills and the villi in the small intestine are adapted so that they have short diffusion distance, big concentration difference and large surface area. This means that they are adapted to have a rapid rate of diffusion. This is important for the survival of animals because they need to obtain as much oxygen, sugar and amino acids to meet the needs of metabolism and they need to expel waste substances such as urea as quickly as possible.