Diffusion and Active Transport

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration.
It is a passive process, which means it does not require energy from the cell.
Diffusion continues until the concentrations are uniform and evenly spread; this state is known as equilibrium.
Rates of diffusion can be affected by factors such as the concentration gradient, temperature, and surface area of the membrane.
Simple diffusion occurs when small, non-polar molecules move directly across the cell membrane.
With facilitated diffusion, transport proteins in the cell membrane help larger or polar molecules move across.

Active transport entails the movement of molecules across a cell membrane from an area of lower concentration to an area of higher concentration.
Unlike diffusion, active transport is an active process which requires energy in the form of ATP.
Transport proteins, specifically known as pumps, are involved in active transport to move molecules against the concentration gradient.
Examples of molecules that are transported in this way include ions such as sodium, potassium and calcium, and also glucose.
Active transport is essential for many cellular functions including maintaining concentrations of ions, uptake of glucose in the intestines and kidneys, and loading of photosynthate or solute ions into phloem sieve tubes.

Both diffusion and active transport are ways that cells can transport substances across their membranes, but they operate in different ways.
Diffusion is passive and moves substances from regions of higher to lower concentration while active transport is an energetic process which moves substances against their concentration gradient.
The energy for active transport mainly comes from ATP produced by cell respiration.