11 Properties of Life
All groups of living organisms share several key characteristics or functions:
- Cells / Order
- Sensitivity or response to stimuli
- Reproduction
- Evolution and Adaptation
- Growth and development
- Regulation
- Homeostasis
- Metabolism
When viewed together, these eight characteristics serve to define life. Let’s examine what each of these characteristics means to in a scientific sense.
Cells / Order
Organisms, in the most basic form, consist of highly organized structures that are made up of one or more cells. Even very simple, single-celled organisms are remarkably complex. Inside each cell, atoms make up molecules. These in turn make up cell components or organelles. Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms in that their cells can be specialized to perform specific functions.
Sensitivity or Response to Stimuli
Organisms respond to diverse signals from the environment (stimuli). For example, plants can bend toward a source of light or respond to touch (Figure 1.3). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis). Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a negative response.
Reproduction
Single-celled organisms reproduce by duplicating their DNA (deoxyribonucleic acid, the genetic material; see Figure 7) and then dividing it equally as the cell prepares to divide to form two new cells.
Many multicellular organisms produce specialized reproductive cells that will form new individuals. When reproduction occurs, DNA is passed along to an organism’s offspring. Genes, made up of DNA, are the basic units by which traits are passed from parent to offspring. DNA, and the information that it encodes in genes, is the reason that offspring will belong to the same species as parents and will have similar characteristics.
Evolution and Adaptation
All living organisms exhibit a “fit” to their environment. Biologists refer to this fit as adaptation and it is a consequence of evolution by natural selection, which operates in every lineage of reproducing organisms. Examples of adaptations are diverse and unique, from heat-resistant Archaea that live in boiling hot springs to the tongue length of a nectar-feeding moth that matches the size of the flower from which it feeds. All adaptations enhance the reproductive potential of the individual exhibiting them, including their ability to survive to reproduce. Adaptations are not constant. As an environment changes, natural selection causes the characteristics of the individuals in a population to track those changes.
NOTE: “Adaptation” in a biological concept is used differently from how you might use it in normal conversation. Adaptations are changes that occur in the characteristics of an organism due to evolution. These changes take place over many generations and are (mainly) d