Important distinctions have also been made between hard systems – technical in nature and amenable to methods such as systems engineering, operations research, and quantitative systems analysis – and soft systems that involve people and organisations, commonly associated with concepts developed by Peter Checkland and Brian Wilson through Soft Systems Methodology (SSM) involving methods such as action research and emphasis of participatory designs. Where hard systems might be identified as more "scientific", the distinction between them is often elusive. Cultural system
A cultural system may be defined as the interaction of different elements of culture. While a cultural system is quite different from a social system, sometimes both together are referred to as a "sociocultural system". A major concern of the social sciences is the problem of order. Economic system
An economic system is a mechanism (social institution) which deals with the production, distribution and consumption of goods and services in a particular society. The economic system is composed of people, institutions and their relationships to resources, such as the convention of property. It addresses the problems of economics, like the allocation and scarcity of resources. The international sphere of interacting states is described and analysed in systems terms by several international relations scholars, most notably in the neorealist school. This systems mode of international analysis has however been challenged by other schools of international relations thought, most notably the constructivist school, which argues that an over-large focus on systems and structures can obscure the role of individual agency in social interactions.
Mechanism
Diphtheria toxin (DT) is produced only by C. diphtheriae infected with a certain type of bacteriophage. Toxinogenicity is determined by phage conversion (also called lysogenic conversion); i.e, the ability of the bacterium to make DT changes as a consequence of infection by a particular phage. DT is encoded by the tox gene. Strains of corynephage are either tox+ (e.g., corynephage β) or tox- (e.g., corynephage γ). The tox gene becomes integrated into the bacterial genome. The chromosome of C. diphtheriae has two different but functionally equivalent bacterial attachment sites (attB) for integration of β prophage into the chromosome. Diphtheria toxin precursor is a protein of molecular weight 60 kDa. Certain proteases, such as trypsin, selectively cleave DT to generate two peptide chains, amino-terminal fragment A (DT-A) and carboxyl-terminal fragment B (DT-B), which are held together by a disulfide bond. DT-B is a recognition subunit that gains entry of DT into the host cell by binding to the EGF-like domain of heparin-binding EGF-like growth factor  on the cell surface. This signals the cell to internalize the toxin within an endosome via receptor-mediated endocytosis. Inside the endosome, DT is split by a trypsin-like protease into DT-A and DT-B. The acidity of the endosome causes DT-B to create pores in the endosome membrane, thereby catalysing the release of DT-A into the cytoplasm.Fragment A inhibits the synthesis of new proteins in the affected cell by catalyzing ADP-ribosylation of elongation factor EF-2—a protein that is essential to the translation step of protein synthesis.