Summary
Highlights
Diffusion is the spreading out of particles, resulting in a net movement from an area of higher concentration to an area of lower concentration. This process is how molecules enter and leave cells.
Key molecules that move in and out of cells by diffusion are oxygen, carbon dioxide, and urea. Oxygen diffuses into cells for respiration, carbon dioxide diffuses out as a waste product, and urea, another waste product, diffuses out into the bloodstream.
The first factor affecting the rate of diffusion is the difference in concentrations, known as the concentration gradient. A greater concentration gradient leads to faster diffusion.
The second factor is temperature. Higher temperatures increase the rate of diffusion because particles have more kinetic energy and move faster.
The final factor is the surface area of the membrane. A larger surface area of the cell membrane allows for a greater rate of diffusion.