Chapter 15: Classification

1. Chapter 15: Classification

2. Why Classify? • To study the diversity of life, scientists use a classification system to name organisms and group them in a logical manner. • Two features of biological classification systems: • 1. Each organism has a universally accepted name. • 2. Organisms are grouped based on shared biologically important traits. • Taxonomy - science of naming and classifying organisms.

3. History of classification • Aristotle - first person who grouped plants and animals based on structural similarities. • Greeks and Romans continued grouping organisms into basic categories like: horses, dogs, oaks, etc. • In the middle ages, each category was called a genus and each was given a Latin name (ex. Cats - Felis). • Latin phrases (called polynomials) used to describe the physical details of each species of a genus. • Polynomial system was very confusing - up to 20 words were used to describe each species! • Ex. “Oak with deeply divided leaves that have no hairs on their undersides and no teeth around their edges” • Linnaeus - person who simplified system of naming organisms.

4. Scientific names are universal • Linnaeus developed a 2-word Latin naming system; this system is called binomial nomenclature. • When naming using binomial nomenclature, each organism has a scientific name - unique 2-word name for a species.

5. Scientific names are universal • The first word of a scientific name is the genus to which an organism belongs. • An organisms is assigned a genus based on its major characteristics. • Ex. Oak trees all produce acorns and are put into the genus Quercus.

6. Scientific names are universal • The second word of a scientific name is the species name which identifies a particular organism within its genus. • Ex. Red Oak - Quercus rubra White Oak - Quercus phellos • Notation alert! • The first letter of the genus is always a capital letter, the first letter of the species is always a lowercase letter! • The scientific name is always italicized! • Dog - Canis familiaris • Cat - Felis domesticus

7. Taxonomy • After naming organisms, Linnaeus group them according to their body structures. • Organisms that shared important characteristics were classified into the same groups. • These groups are called taxa (singular, taxon). • Taxonomy - the science of naming organisms and assigning them groups or taxa for classification.

8. Classification via hierarchies • Organisms are classified into seven different taxa. • The seven taxa include: Kingdom, Phylum, Class, Order, Family, Genus, Species. • Pneumonic: King Phillip Came Over For Great Spaghetti. • Kingdom is the largest and most general / inclusive classification group. • Species is the smallest and most specific group. • Subspecies - least inclusive, not every member of a species is alike. • Ex. red squirrel, southern red squirrel

9. Classification via hierarchies • Honeybee: • Kingdom - Animalia • Phylum - Arthropoda • Class - Insecta • Order - Hymenoptera • Family - Apidae • Genus - Apis • Species - Apis mellifera

10. Problems with traditional classification • Sometimes organisms that are quite different from each other evolve similar structural characteristics. • These similarities make it difficult for taxonomists to decide how organisms should be classified. • Organisms share certain traits because they share evolutionary history. • Biologists today group organisms into categories that represent lines of evolutionary descent, not just physical similarities.

11. Classification using cladograms • Cladistic analysis identifies and considers only those new characteristics of organisms that arise as lineages evolve over time. • Cladogram - a diagram that shows evolutionary relationships between organisms. • Clade - groups on cladograms. • The larger clade on a cladogram contain increasingly smaller clades that share the traits of the clades before them, but also exhibit distinct changes as the organisms evolves.

12. Example cladogram • Derived characteristics - characteristics that appear in recent parts of a lineage but not in its older members. • Primitive characteristic - characteristics shared by all organisms in a lineage.

13. Similarities in DNA • The genes (DNA) of organisms often show important similarities at the molecular level. • These similarities can be used as a criteria for determining classification of the organisms. • The more dissimilar the genes are between organisms, the more evidence there is indicating how long ago the two species shared a common ancestor.

14. Six kingdoms of life • There are six kingdoms into which living organisms are grouped: • Archaebacteria • Eubacteria • Protista • Fungi • Plantae • Animalia • LEARN CHARACTERISTICS OF EACH!

15. Dichotomous keys • Dichotomous key - tool that allows users to identify organisms in the natural world. • Consist of a series of questions or choices that lead the user to the correct identification of the organism. • Like playing “20 Questions”. • Dichotomous means “divided into two parts”. • Dichotomous keys always give two choices at each step - follow the directions in the key (answering questions as you go) to identify the organism.

16. To USE a dichotomous key… • Some hints include: • Always read both choices, even if the first seems to be the logical one at first. • Be sure you understand the meaning of the terms involved. Do not guess! • When measurements are given, measure! Do not guess! • If the choice is not clear, for whatever reason, try both divisions. If you end up with two possible answers, read descriptions of the two choices to help you decide. • Having arrived at an answer in a key, do not accept this as absolutely reliable. Check a description of the organism to see if it agrees with the unknown specimen. If not, an error has been made.

17. To MAKE a dichotomous key… • Some hints include: • Use measurements. • Make the choice a positive one - something "is" instead of "is not". • If possible, start both choices of a pair with the same word. • If possible, start different pairs of choices with different words. • Precede the descriptive terms with the name of the part to which they apply.