4–10 — RESOURCE-ACQUISITION INTERFACE
This level identifies how the resource crosses the organism’s functional boundary.
Operational definition
Layer type: Boundary-crossing mechanism layer Governs: Items 4–10
Formal definition
The Resource-Acquisition Interface identifies the physical, cellular, anatomical, behavioral, or interorganismal process by which energy-bearing resources, electrons, photons, nutrients, or organic matter become accessible across the focal system’s boundary.
This layer describes how the organism reaches the resource, not what the resource is chemically.
Governing question
By what interface does the usable resource become available to the living system?
Included interface classes
This layer contains:
- extracellular electron access;
- photon capture;
- molecular uptake;
- particulate acquisition;
- extracellular digestion followed by absorption;
- host-resource extraction;
- partner-mediated acquisition.
Inclusion rule
A process belongs here when it performs at least one of these functions:
- intercepts the external energetic input;
- transports a resource across a biological boundary;
- converts an inaccessible resource into an accessible form;
- physically connects an organism to an extracellular electron donor or acceptor;
- uses another organism to capture, transform, or deliver the resource.
Examples of independent classification
The same chemical resource can be acquired through different interfaces.
Organic carbon may be obtained through:
- dissolved molecular uptake;
- prey ingestion;
- extracellular digestion;
- host feeding;
- symbiotic transfer.
Conversely, the same interface can acquire many different resources. Active molecular transport may import:
- sugars;
- amino acids;
- inorganic ions;
- electron donors;
- carbon sources;
- cofactors.
Why extracellular electron access belongs here
An extracellular electrode, mineral, or conductive partner does not constitute a third fundamental source category alongside radiant and chemical free energy.
Instead:
extracellular electron source
→
electron-access interface
→
cellular redox metabolism
The external location and transfer pathway define the interface; the underlying energetic transaction remains redox-chemical.
Exclusion rule
This layer excludes:
- intracellular catabolism;
- electron-transport phosphorylation;
- carbon assimilation;
- ecological trophic role;
- functional allocation.
Acquisition ends when the resource becomes accessible to the focal metabolic system. What happens to it afterward belongs downstream.
5. Photon capture
- chlorophyll or bacteriochlorophyll antenna systems
- reaction centers
- accessory pigments
- retinal proteins
- photosynthetic symbionts
- temporarily acquired chloroplasts
6. Molecular uptake
6.1 Passive uptake
- simple diffusion
- channel-mediated diffusion
6.2 Facilitated uptake
- carrier-mediated transport
- selective permeases
6.3 Active uptake
- ATP-dependent transport
- ion-gradient-coupled transport
- group translocation
6.4 Gas uptake
- carbon dioxide
- oxygen
- hydrogen
- methane
- carbon monoxide
- gaseous nitrogen compounds
7. Particulate acquisition
- phagocytosis
- engulfment
- filter feeding
- grazing
- predation
- particulate detritivory
8. Extracellular digestion followed by absorption
- fungal osmotrophy
- bacterial extracellular hydrolysis
- saprotrophic digestion
- animal digestive systems
- external liquefaction of prey
9. Host-resource extraction
- blood feeding
- sap feeding
- intracellular parasitism
- tissue feeding
- intestinal parasitism
- nutrient withdrawal from host fluids
- exploitation of host metabolic products
10. Partner-mediated acquisition
- cross-feeding
- metabolite exchange
- syntrophy
- mycorrhizal exchange
- photosymbiosis
- gut microbial fermentation
- partner-mediated electron transfer