Chapter 18: Matter, Energy and Organisms
One of the activities that define organisms is that at some point in their life, or throughout it, they grow. Growth requires the acquisition of matter and both the acquisition of matter and the incorporation of this material into a living form (i.e., into biomolecules) involves energy. Both matter and energy are needed but it is important to keep in mind that they are two distinct entities that are NOT interconvertible. The energy transformations that organisms carry out involve manipulations of matter but they DO NOT involve converting matter into energy. Energy is obtained by rearranging matter, mostly by converting carbohydrates and oxygen into carbon dioxide and water. What complicates understanding is that matter is needed in two ways (Fig. 1): (1) materially, providing the materials that become part of the organism, mostly carbohydrates or carbohydrate derivatives, (2) energetically, because energy can be made available as matter is rearranged, e.g., converting carbohydrates and oxygen into carbon dioxide and water. Although matter is being rearranged, it is not being transformed into energy.
Matter, Energy and the Laws of Thermodynamics
Matter and energy are key players in the process of life at all levels: cell, organism, and ecosystem. Both matter and energy are familiar ideas, yet misconceptions are common, especially about energy and the interplay between matter and energy in biological systems. Matter is straightforward: it has mass, occupies space and can be categorized into elements (e.g., carbon, hydrogen, oxygen) that often are usually present in specific mixtures termed molecules (e.g., carbon dioxide, glucose) that have a characteristic composition of elements and are arranged in specific ways. Living things are made of matter and have a characteristic material composition, being made of biomolecules such as proteins, carbohydrates, and nucleic acids. Life may be partly defined by the ability of living things (organisms) to acquire matter and incorporate it into themselves, i.e., to grow. Life can also be defined on the basis of its ability to manipulate matter in characteristic ways that involve energy transfers.
While matter is an easy concept, energy is much more elusive; consider the following:
- Energy has the ability to affect matter by rearranging it or moving it from one place to another.
- Energy is dynamic and the energy associated with a given bit of matter, e.g., a molecule, depends on circumstances; it is a function of the situation matter finds itself in, the speed it is moving, the location that it is in, in particular its position relative to other matter or relative to electric, magnetic and gravitational fields (which are controlled by matter).
- Energy is a property of systems, i.e., an assemblage of matter in a particular place and with specific relationships with each other.
- Energy describes the ability of a given assemblage of matter (a ‘system’) to change the org