Biology Reference
In-Depth Information
A
nutrient substrate
gradient of metabolites produced
by the dark cells
substrate
gradient
substrate
B
threshold
nutrient substrate
gradient of metabolites produced
by the dark cells
substrate
gradient
substrate
C
threshold
nutrient substrate
(adapted from Kupiec, 1986, 1997)
F
IGURE
16. Model of the heap of cells.
The growth of this cell colony depends
on its environment.
A:
Only the cells of the first layer have direct access to the
substrate.
B:
The other cells only have access to the substrate which is diffus-
ing in the colony and forming a decreasing concentration gradient, or access to
the metabolites, which form secondary gradients. Below a certain concentration
threshold, the cells can no longer grow (dark cells).
C:
They must then differ-
entiate to adapt to these microenvironmental conditions and continue to grow
(
light cells).
by the concentrations of nutrient and metabolites. The cells situ-
ated at the lower part of the colony have a microenvironment richer
in nutrient while those at the upper part have a microenvironment
richer in metabolites. To optimise their growth, the cells have to
