Diffusion
The Law of Diffusion states that particles always move from an area of higher concentration to an area of lower concentration until they are evenly distributed (assuming no interference). This gives rise to the most common form of cellular transport - diffusion.
Using this logic, if there is a greater concentration of material x outside the cell than inside it, then material x will go into the cell through diffusion. However, we must also note that not all materials can diffuse directly across a cell membrane. Only molecules that are soluble in the phospholipid bilayer of the cell membrane may do so. Examples include alcohols and steroids.
Diffusion is considered a passive form of transport because it does not require energy to do so. However, adding heat energy to the system can speed up the diffusion process. Other ways to speed it up include increasing the concentration gradient (the difference in concentration), or decreasing the size of the molecules being diffused.
Using this logic, if there is a greater concentration of material x outside the cell than inside it, then material x will go into the cell through diffusion. However, we must also note that not all materials can diffuse directly across a cell membrane. Only molecules that are soluble in the phospholipid bilayer of the cell membrane may do so. Examples include alcohols and steroids.
Diffusion is considered a passive form of transport because it does not require energy to do so. However, adding heat energy to the system can speed up the diffusion process. Other ways to speed it up include increasing the concentration gradient (the difference in concentration), or decreasing the size of the molecules being diffused.