Last modified: Mon 4/28/97 0030 PDT
 Canon Terms |
Object | Classes | Organism; LivingOrganism; Fossil; FossilOrganism; UnicellularOrganism; MulticellularOrganism; Tissue; Organ; OrganSystem |
| Instances | (none) | ||
| Event | Classes | AsexualReproduction; SexualReproduction; Evolution; Speciation | |
| Instances | (none) |
An organism is a Living Agent which carries (possibly multiple instances of) a specific genome.
It is convenient to distinguish between organisms observed while alive (living organisms) from those whose earlier existence is inferred from structures (called fossils) found in rock (fossil organisms). Fossils which record the effects of an organism while living, rather than parts of the organism itself, are called trace fossils. The study of fossils and fossil organisms is the subject matter of paleontology, claimed by both geology (due to the importance of fossils in the study of Earth history) and biology. The study of trace fossils is the subject matter of paleoichnology, part of paleontology.
Organisms are aggregates of cells and dependent biostructures. Organisms which never consist of two or more cells are referred to as unicellular organisms, those which do are multicellular organisms.
It is observed that the cells of multicellular organisms may organize themselves hierarchically at several levels. Specifically, cells of one type may aggregate into structures called tissues; sets of different tissues which interact more closely with eath other than with other tissues are called organs; and sets of different organs which interact more closely with each other than with other organs are referred to as organ systems. This hierarchical structure of a multicellular organism is referred to as its anatomy. The way in which these structures function (i.e. interact with each other and with the organism's environment, giving rise to the processes of metabolism and reproduction) is the organism's physiology. The study of organisms' anatomy is the subject matter of comparative anatomy, part of comparative biology. The study of organisms' physiology is the subject matter of comparative physiology, also part of comparative biology. The study of tissues is the subject matter of comparative histology, part of comparative biology.
The process of reproduction may involve the copying of the genome of just one parent organism (asexual reproduction) or it may mix the genomes of two parent organisms (sexual reproduction). In either case, it is possible that the new genome is not perfectly identical to the parent genome(s). Over numerous generations, genomes may diverge significantly from that of a common ancestor (speciation). This process of genome change (as well as the concomitant changes in the organisms carrying those genomes) is referred to as evolution. It is evolution which has led to the great diversity of Earth organisms (the only organisms currently known to humans). The study of evolution is the subject matter of evolutionary biology, part of biology.