active transport is the pumping of ions or molecules across a cell membrane with the help of special enzymes, the so called transport proteins, which are built in or bound to the membrane of the cell. Active transport is going into the opposite direction than simple diffusion. While diffusion is a spontaneous process driven by the concentration-difference between two sides of the cell membrane. Molecules or ions are actively transported into the opposite direction (toward the higher concentration side of the memebrane) than by diffusion, so that active transport requires energy.
Active transport in the cells is able to pump molecules through membranes into the higher concentration space, e.g. more and more hydrogen ions into the stomach to reach a very acidic pH value necessary for digestion.
Nutrient uptake is ensured by active trasnport, even if the nutrient ions and molecules are in very low concentration outside the cell.
Ion pumps create charge differences and charge gradients in cell organelles.
Active transport is able to restrict the diffusion of hazardous or any unwanted ions and molecules into the cell.
Active transport may happen by direct energy uptake with the help of the transmembrane enzymes transporting the ions and molecules and having ATP-ase activity at the same time. The other mechanism of molecular trasport utilises the electrochemical potential difference, which is created by pumping ions (by energy consuming active transport) out of cells.
Some toxins e.g. digitalis inhibit the active transport of the cells.
impact of transportation-related activities on the environment, in particular, those impacts dealing with air pollution, noise, displacement of people and businesses, disruption of wildlife habitats, and overall growth-inducing effects.