Classification of Life

Why Classify? There are more than 2 ½ Million species of organisms on earth – and more to be discovered! When you go into the grocery store, how do you know where to find the dairy, meat, cereals, etc...? We need some system to help organize the classification of living things How do you know that a dog and a wolf are related.

We talked about relationships during the last chapter. How can we use those ideas to help us place organisms into a logical order? Accepted biological classification systems: They assign a single universally accepted name to each organism. Why? They can discuss with scientists from other countries or across the street. They place organisms into groups that have real biological meaning.

Biological Classification Aristotle was one of the first people to classify organisms. His categories included only 2 categories - plants and animals. By 19th century, scientists began using Latin or Greek words to name organisms, but Great detail was used “Oak with deeply divided leaves that have no hairs on the underside and no teeth around their edges” may have been one tree’s name.

??? Caused confusion: Scientists might call characteristics different things – serrated edge or saw tooth Organisms may have more than one name

Carolus Linnaeus Swedish Botanist Binomial Nomenclature – two names for each organism Pagurus longicarpis, Acer palmatum, Homo sapien

Genus and species – Genus is capital, species is lower case, both are italicized or if you write them down, they should be underlined. After naming organisms, Linnaeus grouped them together based on body structures they shared. Groups of organisms are called taxa (singular is taxon). The science of naming organisms is called taxonomy. Smallest taxon is species – a group of similar looking organisms that can breed and produce fertile offspring

What is a species? If two species share the same characteristics, but are distinct, they may belong to the same Genus.

What is a species? Felis domesticus (common house cat), Felis concolor (mountain lion)

What is a species? Lions (Panthera leo) and tigers (Panthera tigris) are still cat like, but different enough to be classified as different Genus.

DaringDomain King Kingdom Philip Phylum Came Class Over Order For Family Great Genus Spaghettispecies

Taxonomy Today Not always so cut and dry. Species breed with each other – they share a common gene pool

Above that, there is not a clear biological identity Sometimes organisms are “moved” from one to another classification 6 Kingdom System

Over the years, it became obvious that 2 kingdoms were not enough. Microscopic organisms looked and acted different than other organisms Euglena Bacteria – lack nuclei, mitochondria, chloroplasts

Classification is based on Structural similarities –presence of many shared physical traits implies close relationship –dandelions and sunflowers have same flower and fruit structure Breeding Behavior –frogs that live in the same areas and look similar but males make different sounds to attract mates and only mate with members of their own group = different species

Classification is based on Geographical distribution –Darwin’s finches Chromosome comparisons –# and structure of chromosomes –cauliflower, cabbage, kale, and broccoli look different, but have almost identical chromosomes Biochemistry –DNA sequences compared

Cladistics – system of classification based on evolutionary relationships Cladogram – model of phylogeny –A method used to construct a hypothetical evolutionary tree

Domains Largest group – even larger than kingdom 3 domains –Archaea –Bacteria –Eukarya

Bacteria –prokaryotic –cell walls with peptidoglycan –Unicellular –can be autotroph or heterotroph –what we think of as bacteria

Archaea –cell walls lack peptioglycan –prokaryotic –unicellular –autotroph or heterotroph –Live in extreme environments –have DNA

Eukarya fungi plantae animalia

Fungi mold, yeast, mushrooms cell wall w/out cellulose heterotrophic many nuclei do not always have separate cells divided by complete cell walls

Plantae multicellular cell walls with cellulose autotrophic – photosynthesis using chlorophyll

Animalia multicellular heterotrophic cell membranes – no cell walls

Taxonomy is not constant. What was once 2 kingdoms was found to be inadequate, now there are 3 Domains and 6 kingdoms. Algae have been classified as plants, then protists, now plants again.