# PLANTS and BIOLOGICAL FILTRATION article



## DataGuru (Mar 11, 2005)

We were just reading over your Plants and Biological Filtration article again. In our tanks, there's a mix of ammonia and ammonium that depends on pH and water temp. In your article you talk about plants prefering ammonium (NH4+). Is there any difference between ammonium uptake and ammonia (NH3) uptake?


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## dwalstad (Apr 14, 2006)

There's a difference in uptake mechanism.

Plants can take up ammonia, because it is an uncharged molecule, without any effort-- ammonia just diffuses across the cell's lipid bilayer directly into the plant. To take up ammonium, which has a positive charge, the plant will need to use an ammonium transporter to bring it into the cell. 

In general, compounds like NH3, CO2, H2S are toxic, because the plant cannot regulate their uptake. These compounds diffuse freely across the cell membrane. If the outside concentration is high, the plants will be "cooked". 

In contrast, cells can regulate the uptake of NH4+ (ammonium). They only bring it in when they need it. Thus, ammonium is not very toxic.

This is a general phenomenon that applies to all organisms-- plants, fish, bacteria, humans. All cells have a membrane lipid bilayer that prevent molecules with an electrical charge from freely diffusing in. Thus, cells can regulate electrically charged molecules. However, cells can't regulate uncharged gases like NH3, CO2, H2S, etc.


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## DataGuru (Mar 11, 2005)

Interesting... Thanks Diana!


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