code: def find_interchange_biomass_reactions(model, biomass=None):
      
      boundary = set(model.boundary)
      transporters = find_transport_reactions(model)
      if biomass is None:
          biomass = set(find_biomass_reaction(model))
      return boundary | transporters | biomass
docs: Return the set of all transport, boundary, and biomass reactions.
  
      These reactions are either pseudo-reactions, or incorporated to allow
      metabolites to pass between compartments. Some tests focus on purely
      metabolic reactions and hence exclude this set.
  
      Parameters
      ----------
      model : cobra.Model
          The metabolic model under investigation.
      biomass : list or cobra.Reaction, optional
          A list of cobrapy biomass reactions.