Diffusion is the movement of molecules from high to low concentration.
Factors that influence the rate of diffusion:
Temperature: Higher, quicker diffusion
Concentration gradient difference: Larger, quicker diffusion
Distance: Smaller, quicker diffusion
Surface area to diffuse through: Bigger, quicker diffusion
Osmosis is the process by which water moves in and out of cells. Osmosis happens when a partially permeable cell membrane separates 2 solutions. The partially permeable membrane only lets water molecules through it.
The water molecules can move in either direction, but those on the right are attracted to the sugar molecules. This slows them down (they have less kinetic energy). As a result of this, the water molecules diffuse more from left to right than from right to left than from left to right. In other words, there is a greater diffusion of water molecules from the dilute solution (left) to the more concentrated solution.
Active Transport is when molecules are transported across a membrane. Carrier Proteins are found in the cell membrane. Energy from respiration is used to change the carrier proteins' shape. As the carrier protein changes its shape the molecule is released on the other side of the membrane. Molecules can only be transported in one direction- against their diffusion gradient. The carrier protein is then changed back to its original shape.