Active transport.
Active transport is the movement of particles against a concentration gradient, from an area of low concentration to and area of high concentration, using energy released by respiration.

Active transport is the opposite of diffusion.
Like Diffusion and Osmosis, Active transport is the movement of particles in and out of cells.

Factors Affecting substance movement:
Surface area to volume ratio,
Temperature,
Concentration Gradient.

Surface area to volume ratio.
The rate of diffusion, osmosis and active transport is higher in cells that have a larger surface area to volume ratio.

A 2 cm2 cube cell will have:
Area 2x2x6 (faces) = 24cm2
Volume 2x2x2 = 8cm3
Ratio 24:8 = 3:1

In the example movement in and out of the cell will be faster, as there is a higher surface area to volume ratio

Concentration Gradient.
Substances move faster in and out of cells if there is a big difference in concentration gradient. When there are a lot more particles on one side, there are more to move across.