Active Transport

There are times when cells need to move chemicals across the cell membrane against the concentration gradient (i.e. from a low concentration to a high concentration). This requires energy, as the chemicals need to be pumped across the cell membrane.

The cells of the small intestine absorb some food particles by active transport. The cells lining the kidney nephrons (see kidney) absorb vital chemicals like glucose from a filtrate, which would otherwise be lost in urine. Cells, which use active transport a great deal, will have large quantities of mitochondria to supply them with energy.   Obviously there needs to be a good supply of oxygen and glucose so that energy can be released by respiration.

Substances are selectively transported. The cell can choose which chemicals are pumped into or out of the cell. For example, nerve cells actively pump potassium inside the cell while pumping sodium out of the cell.

This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

2005 Psionica