Systems, Parameters and State Functions

The question of what kind of model we should use, what we should consider as a system, and what are its elements, depends exclusively on the particular problem, and the corresponding point of view. An element may be a system itself, extending the problem. An organism, for example, as an element in an ecological system can become a system itself, if we ask a physiological question such as what are the interactions between its organs. The organ can be considered a system of cells, the cell as a system of organelles, and so on.

A dynamic system can be analyzed in different ways. In contrast to system theory, which calculates the kinetic interplay of individual elements, thermodynamics considers a system simply as a continuum which stands in a defined interrelation with its environment. The limit of this continuum does not have to be a wall or a membrane. It can also be a process that changes the quality of the subject of study. Chemical reactions as well as processes of proliferation and evolution are examples of this.

In thermodynamics, systems are classified as follows according to the nature of their boundary against their environment:

- The isolated system: this is an idealized system that does not exchange any kind of energy or matter with its environment.

- The closed system: this system can exchange all kinds of energy with its environment, but not matter.

- The open system: it can exchange both energy and matter with its environment.

The closed system can be influenced by its environment, and can cause changes in its environment. However, it cannot be involved in an exchange of matter.

The state of a system can be described by a number of state variables. These are either extensive or intensive parameters. Intensive parameters are non additive. They are independent of the size of the system (e.g. temperature, concentration, pressure, density). Extensive parameters on the other hand, are additive when two systems are combined (e.g. mass, volume).

Changes in a system are often characterized by differentials of its state variables. A differential describes a very small change of a dependent variable (dy), if in a function y = f(x), a small change in the variable (dx) occurs. It can be calculated from the product of the first derivative of the function f(x), multiplied by dx: dy=f'(x)dx.

Define the following words

A derivative, a differential, the interplay, a continuum .

Complete the sentences

1. The question of what kind of model we should use…

2. The organ can be considered…

3. In contrast to system theory…

4. In thermodynamics, systems are classified…

5. Changes in a system are often characterized…

6. The closed system can be influenced by…

Put appropriate forms of the words into the gaps

In statistics, frequency is defined as the proportion of individuals falling within a certain category in relation to the total number of individuals under ______________(consider).

In general, the ______________(extend) to which gene flow can hinder the effects of natural selection should depend on the relative strengths of the two processes.

To confirm the ______________(involve) of microtubules as sensors of directional force in cell elongation, some protoplasts were incubated prior to centrifugation with a chemical herbicide, APM, which disrupts microtubules.

Species with little genetic ______________(vary) are generally at significantly greater risk of extinction than more ______________(vary) species, simply because they have a more limited arsenal with which to respond to the vagaries of environmental change.

The complex differentiation that we associate with advanced life-forms ______________(depend) on multicellularity and sexuality, which must have been highly advantageous to have evolved ______________(depend) so often.

The cells tend to hang together in chains, a feature that calls to mind the ______________(derive) of single-celled yeasts from multicellular ancestors.