Living Systems Structure

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Conceptual Tools
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At each of the three system levels, each living entity can be viewed as an individual living system. Each individual cell, organism and superorganism is said to be "alive" because it has a specific set of functional characteristics, often referred to as "life functions." The continuous performance of these life functions enables the living system to interact with its changing external environment while maintaining a protective and consistent set of internal conditions.
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To help understand the underlying structure that produces these life functions, three theoretical concepts are employed:
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Systems Theory:	A functioning system is made up of interacting subsystems that work cooperatively and continuously to produce and sustain a particular result.
Aggregate Objects:	An aggregate object is a unified whole whose unique properties emerge from the characteristics of its component objects together with the constraining relations that bind them together.
Organizational Theory:	An organization embodies strategies and structures that enable members to work together as an ongoing group to collectively accomplish a particular purpose.

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Each of these theoretical concepts provides a helpful but incomplete view of the internal structure of living systems. By integrating and synthesizing the three views, a more complete visualization of living systems structure can be achieved.

.Systems View
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A Living System is a system made up of interacting subsystems.

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Each subsystem provides a key characteristic of the overall system. Through their cooperative behavior, the subsystems collectively produce the "life" of the living system and maintain its stable equilibrium. To be living, an entity must maintain a kind of internal environment that is independent from its external environment.
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A living system exhibits homeostasis, the ability to sustain a controlled set of internal conditions in the face of changing external conditions. Living in a real world environment involves interaction and adjustment. Lacking the ability to control its external environment, a living system must have a boundary to protect and insulate its internal operations.
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To live, a living system requires energy and the expenditure of effort to perform the life functions that sustain its internal equilibrium. This energy must be obtained in some form from interaction with an external environment. Energy may be obtained directly, by absorbing radiation, or indirectly by ingesting matter which is then converted to energy.

.Aggregate Object View
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A Living System is an Aggregate Object Constructed from Component Objects.

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A cell aggregate object is constructed from biomolecule objects. An organism aggregate object is constructed from cell objects. And a superorganism aggregate object is constructed from organism objects.
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The Theory of Aggregate Objects provides an architectural perspective that explains how the unique properties of an aggregate object emerge from the characteristics and constraints of its component objects. For example, an automobile's load-carrying capability and top speed emerge from the horsepower of its engine, the shape of its body, the configuration of its suspension subsystem, etc., and the constraining bolts and fasteners that force them to work in unison.
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Aggregate objects can be static or dynamic, so the principle of emergence applies to all physical things including buildings, automobiles, computers and living systems. As a dynamic system, a living system's component objects are constrained to work in unison to collectively produce its emergent life properties. The behavior of cells may be constrained such that their collective behavior produces a higher-level organism. Similarly, the behavior or organisms may be constrained to produce a higher-level superorganism.

.Organizational View
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An Organization Unit Orchestrates the Work of Component Objects.

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Organizational Theory provides a social perspective that focuses on the control mechanisms that are required to orchestrate work by members of a group to collectively produce a common result. For living systems, this brings to light the need for organization units as intermediate structures between a higher-level aggregate living system and its lower-level component living systems.
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These organizational principles are found to apply at all three levels of living system. A cell uses organelles to orchestrate the work of its component biomolecules. An organism uses organs to orchestrate the work of its component cells. And a superorganism uses organizations (business or non-profit) to orchestrate the work of its component human organisms.

The Role of Governance
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Governance Operates and Controls Living System Actions.

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Governance is a special kind of subsystem that directs and coordinates the other subsystems to perform the functions necessary for life. It is the high-level control mechanism by which a living system sustains its health and existence within a changing environment.
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A governance mechanism does not have the capacity to interface directly with the living system's components. It directs action by the organization units, which in turn orchestrate detailed work to be performed by the components. To compensate for this indirect coupling, the organization units provide sensory feedback on the collective results of actions being taken.

Architectural Framework
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By integrating concepts from the systems, aggregate object and organizations views with the governance, the structure and control mechanisms of living systems can be portrayed. The following table illustrates how the same basic governance-organization-component structure is found at each of the three levels of living system.
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Living Systems Architectural Framework
Living System Level	Governance Mechanism	Organization Unit	Component
3. Superorganism	Government	Organization	Organism
2. Organism	Brain/Spinal Cord	Organ	Cell
1. Cell	Nucleus	Organelle	Biomolecule
0. Biomolecule	- - - -	- - - -	- - - -

The next page Subsystems and Functions provides a list of the basic life functions that are necessary for a living system to exist.