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.

• Daring Domain• King Kingdom• Philip Phylum• Came Class• Over Order• For Family• Great Genus• Spaghetti species

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.