Diffusion

Diffusion is the random movement of molecules/particles from an area of higher concentration to an area of lower concentration along a concentration gradient. It is a slow process and does not require energy (ATP) and therefore is termed as a passive process.

The rate of diffusion increases with:

1.Temperature: when temperature is raised the molecules have more kinetic energy which thus increases the rate of diffusion.

2.Steep concentration gradient.: The more the difference in the concentration gradients the faster will be the rate of diffusion.

3.Distance: The shorter the distance for diffusion the faster is the diffusion. The wall of the capilllary is only one cell thick, which allows for the exchange of carbon dioxide and oxygen to take place.

4.Size of the particle isinversely proportional to the rate of diffusion. The smaller the particle the faster is the diffusion.

5. Surface area: The greater the surface area to volume ratio the faster is the rate of diffusion. The alveoli have a large surface area to volume ratio and therefore allow for the quick diffusion of gases to take place.

6.Permeability of the  membrane: Though diffusion takes place with or without  the presence of a membrane, if a membrane is present it should be permeable to the diffusing particle.

For the rest of the topic refer to the notes on Plasma Membrane section 1.5.