1.1 Organisms are living objects

In this chapter we introduce some formal definitions that can be useful to build your understanding of what organisms are, and how they function. The first important issue to address is philosophical. From the point of view of materialism, organisms are considered to be living objects. In fact, both living and non-living objects are made of molecules and elements that are subject to the laws of physics and chemistry. However, it should be obvious that the distinction between living and non-living objects is not as straightforward as one might think. Lets for example use chemical analysis to compare the elementary composition of different living and non-living objects, as shown in Table 1.1.

Table 1.1 illustrates the percentages of the most common components of different living and non-living objects: water, lipids, carbohydrates, proteins, nucleic acids and traces of minerals such as iron, zinc or magnesium, and others expressed as percentage.

From examination of Table 1.1 we can distinguish an important fact concerning living objects. Their major component is water! In contrast, the composition of non-living objects can vary widely. In fact, we could choose to compare non-living objects whose composition is close to that of any living object and then ask: what is the fundamental difference between them?

If the particular composition of a material object cannot help us discern between living and non-living entities, it is important to consider alternative explanations. An alternative consideration is related to the way that molecules and elements organize to build living and non-living objects. We can for example think of the rocks that one can find along a stream of water, like a river or a lake. The structure of those pebbles is defined by the minerals present in them, and the way those components have been shaped by physical forces and chemical processes throughout ages. Eventually the structure of such objects is entirely dependent on environmental factors, and systematic analysis of this process of transformation has generated practical knowledge about the natural resources of our planet, such as in the processes involved to generate fossil fuels to name one concrete example.

We could also consider a different type of non-living object. A man made object like a car, has a defined structure, with components that serve different purposes. One can also be sure that somewhere available one can find the blueprint that describes how to make that car, what materials to use and how to assemble them together. In making such an object one can recognize that energy is needed. In fact, to maintain a car more energy is needed, and if we forgot about its maintenance, it is likely that the car would run down over time and become useless. So the point is that to maintain or change their structure, objects need an input of energy. Living objects are distinguished from non-living objects because they are capable of independently maintaining their structure by the use of work and energy, and as we will see later in this chapter, they also possess a blueprint with information to carry out the build up and maintenance of their structure. To sum up, organisms are the material structure of living objects, and are distinguished from non-living objects in their independent use of energy to maintain their organization. To understand more about the scope and limits of life in our planet, lets turn our attention to the properties of their environment, and thus we turn to the history of Earth, our planet.