1. How is every organism classified
How is every organism classified? Using Dichotomous Keys How does every species get a unique name? Binomial Nomenclature First, let’s review

2. Remember the taxa?

3. This plant example shows how the number of species decreases with each taxa level.

4. How do scientists determine species?
A biologist thinks they have discovered a new species. How can they be sure? There are three different species concepts used to classify organisms in taxonomy.
Biological species concept – organisms can successfully breed and produce fertile offspring. This widely used concept only works for living, sexually reproducing organisms.
Morphological species concept – comparing the measurements and physical descriptions. Often used for plants or asexually reproducing organisms.
Phylogenetic species concept – looks for evolutionary relationships between organisms. Usually based on DNA studies or fossil evidence.

5. Dichotomous Keys
Dichotomous means to divide in two. Scientists use a dichotomous key and ask yes/no questions to classify a newly discovered organism compared to existing organisms.

6. Dichotomous Keys
The questions biologists ask in a dichotomous key are based on known species characteristics of organisms. The choice of one alternative yes or no answer determines the next step in the dichotomous key. For example:
Does it have feathers? No
Does it have legs? Yes
Then it must be a lizard.

7. Identify the mammal on the right. Circle each answer.

8. Dichotomous Key Pictures
A dichotomous key can be shown as a branching tree diagram with characteristics on each branch. The questions start with
Is it multicellular?
Does it have tissues?
Radial symmetry?
Bilateral symmetry?
These characteristics classify animals.

9. The same questions in a different format

10. Using a morphological species concept can give a different classification than phylogenetic species concept. So it can be difficult to classify a newly discovered organism. What is different here?

11. Binomial Nomenclature
Your newly discovered organism now needs a name. Carolus Linnaeus developed the binomial naming system so every species has a unique two part scientific name. The rules are:
The scientific name consists of the genus and species.
Both words are italicized or underlined.
Genus is always capitalized.
species is always lower-case.
Both name are in Latin.
The species name must be unique in the same Genus.
For example, Ursus arctos or Homo sapiens

12. What is the honey bees’ scientific name?
And the Large Milkweed bug?
Apis mellifera
Oncopeltus fasciatus

13. Why use scientific names?
Common names of an organism are different in every language. Durian’s scientific name is
Durio zibethinus
Look at p 395 in your text. Imagine how hard it must be for someone learning English to understand the meaning of “fish” in all those common names.