Distinguish between diffusion and active transport in terms of
Diffusion: energy involvement?
Active transport: Energy involvement?
Diffusion is when molecules move from greater concentration to an area with less concentration, with no added energy needed. For example, if you have a beaker of water, and drop some food coloring into the water, there will be a concentrated spot of food coloring which will gradually disperse in all directions from high to low concentrations, until an equilibrium is achieved. With the cell membrane, as long as there is a concentration gradient from high on one side of the membrane to low on the other side of the membrane, and the particle size is small enough, diffusion across the membrane will occur. Active transport is when molecules are transported from low to high concentration, against the gradient. This requires ATP which provides energy to the cell to make it happen. An example is the kidney cells which filter urea from the surrounding blood. There will be a greater concentration of urea in the kidney filtrate, than in the blood. The kidney cells use energy to insure that the blood is continually filtered and that active transport allows the movement of these wastes from low to high concentration.