Substrate (thing)

1. The specific molecule an enzyme acts upon.
2. A stationary surface upon which organisms, cells or chemicals can attach.
   For example:
   • cells in culture on a plastic or glass substrate
   • oyster larvae settling on a patch of bare rock (a hard substrate)
   • worms burrowing into mud or other sediment (a soft substrate).

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.