Specialised Exchange Surfaces

These types of exchange surfaces are parts of an organism that exchange substances with the exterior envorment. 

Our exchange cells in our bodies are the Villi, and the Alveoli.
Its job is to exchange Oxygen and Carbon dioxide in our blood, but the Villi, which are our intestines, help with absorbing glucose and amino acids.

The roots in the bottom of the plant have their root hair cells, which help absorb the water in the surrounding soil, along with the leaves, to help them absorb CO2  in the air.

Something to help with these exchange surfaces is a large surface area, so by having hundreds of millions of Alveoli in our lungs, it makes it a larger surface area, having a large surface area increases the amount of diffusion and can also help with the diffusion rates. 

Another thing about diffusion surfaces is that they are often very thin because it makes the substances diffuse over a short distance, for root hair cells, the water only has to diffuse through a thin cell wall and membrane,
this is known as a 'short diffusion distance', which increased the speed with which the plant can absorb. 

Other types of diffusion surfaces are blood, as the blood has to flow and diffuse throughout the body, so having glucose dissolve into the blood that gets taken away to the intestines to then be replaced by more blood.

Another good thing to keep in mind is a 'good supply of external mediums', a good example of this is keeping a good supply of Oxygen for your lungs, when you breathe the Oxygen mixed with the Alveoli, which helps keep a steady concentration gradient for your bloodstream.