36–41 — MATTER ASSIMILATION
Energy flow must be kept distinct from matter flow.
Operational definition
Layer type: Biomass-construction layer Governs: Items 36–41
Formal definition
The Matter Assimilation and Stoichiometric Constraint layer identifies which external elements enter the living system, how they are converted into biologically usable forms, how they are incorporated into biomass, and how their relative availability constrains the use of acquired energy.
Governing question
What matter is required to construct and maintain this living system, and in what proportions must it be supplied?
Included material domains
- carbon;
- nitrogen;
- sulfur;
- phosphorus;
- minerals;
- trace elements;
- elemental-ratio constraints.
Inclusion rule
A process belongs here when an external substance becomes part of:
- structural biomass;
- proteins;
- nucleic acids;
- membranes;
- cofactors;
- enzymes;
- storage material;
- reproductive material;
- functional intracellular pools.
Uptake-versus-assimilation distinction
Uptake means crossing the boundary.
Assimilation means incorporation into the organism’s usable biochemical organization.
A molecule may be:
- taken up and oxidized without substantial incorporation;
- taken up and later excreted;
- assimilated into biomass;
- transformed and stored;
- transferred to another organism.
Energy-versus-matter distinction
Energy alone cannot produce growth.
Biomass construction requires:
usable free energy
+
reducing power
+
carbon
+
nitrogen
+
phosphorus
+
sulfur
+
minerals
A system may possess abundant chemical energy but remain growth-limited by an essential element or by an unfavorable elemental ratio.
Exclusion rule
This layer does not classify:
- the energetic source of the metabolism;
- the acquisition interface;
- the final functional purpose;
- the ecological source organism.
It classifies the material side of living organization.
36. Carbon assimilation
36.1 Inorganic-carbon fixation
CO_2/HCO_3^- → organic biomass
Subclassified by the specific carbon-fixation pathway.
36.2 Organic-carbon assimilation
Organic molecules are:
- imported
- digested
- disassembled
- transformed
- reassembled into biomass
36.3 Mixed-carbon assimilation
Both inorganic carbon fixation and organic-carbon uptake contribute.
37. Nitrogen assimilation
Sources may include:
- ammonium
- nitrate
- nitrite
- molecular nitrogen
- amino acids
- proteins
- host-derived nitrogen compounds
38. Sulfur assimilation
- sulfate
- sulfide
- sulfur-containing amino acids
- organic sulfur
- elemental sulfur intermediates
39. Phosphorus acquisition
- inorganic phosphate
- dissolved organic phosphorus
- phosphonates
- stored polyphosphate
40. Mineral and trace-element acquisition
- iron
- magnesium
- calcium
- potassium
- sodium
- zinc
- copper
- molybdenum
- nickel
- cobalt
- selenium
- other cofactors
41. Stoichiometric constraint
The available proportions of carbon, nitrogen, phosphorus, sulfur, and other elements can limit how effectively acquired energy becomes new biomass.
Thus:
available energy alone does not determine growth
Growth also requires the correct matter, redox balance, and elemental ratios. Ecological stoichiometry explicitly links elemental supply, organismal demand, food webs, and ecosystem metabolism. (PubMed Central (PMC))