In modern biology, there are three approaches to classifying organisms: systematics, cladistics and molecular evolutionary taxonomy. They are all based on organisms' relation to each other, but use different indicators to assign the degree of relationship.
Modern taxonomy, or classification system, originated in the 18th century, from the works of a Swedish botanist Carolus Linnaeus. He classified living beings based on similarities between them. Organisms which could interbreed were put in one species. There are levels of organization above species: genus, to which a number of closely-related species belong, a family, which consists of related genera, and order, which includes similar families. Class, phylum and kingdom are the three subsequent top levels of the system. These large groups can include sub-groups, for example, subphylum, or be a part of a supergroup, for example, a superclass.
When Carolus Linnaeus was developing his system, evolution had not been a scientific fact yet. Once scientists started studying how different organisms are related to each other based on a common ancestor they share, classification has also moved on. The phylogenetic classification system, or systematics, lists clades of organisms, organized into right-angled diagrams, which have a common ancestor. In cladistics, the separation is made at the point when a trait, which makes a particular species unique, arises. It can be, for example, upright walking for humans. A similar system of molecular evolutionary taxonomy focuses on the emergence of genetic differences between species.Learn More
To access the online version of the Holt "Modern Biology" textbook, students need to obtain a key code for the book. Holt assigns a key code to schools that register for its online programs. If students do not have this code, they should ask their school's technology administrator for it.Full Answer >
There are many reasons that classifying organisms is important, such as helping understand the genetic relationships between different groups and species, helping with wide studies of organisms and helping to develop new biological sciences such as biogeography. Each of the groups and sets are created by studying the differences and similarities found in species and organisms known.Full Answer >
A dependent variable in biology is an element that is being tested. It relies on the independent variable, or that aspect of the experiment that the scientist has control over and changes to observe the results on the dependent variable.Full Answer >
In biology and all other forms of science and mathematics, a controlled variable is one that is completely controlled throughout an experiment. Controlled variables stay constant throughout experiments and are carefully controlled and observed.Full Answer >