Dichotomous Keys
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.
1.
_________________ species concept – organisms can successfully breed and produce fertile
offspring. This widely used concept ____________________________________________________
2.
_________________ species concept – comparing the measurements and __________________
descriptions. Often used for _____________ or ____________________ reproducing organisms.
3.
_________________ species concept – looks for ______________________ relationships between
organisms. Usually based on _____________ studies or _____________________________.
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. The questions biologists ask in a
dichotomous key are based on __________________________________________. The choice of one
alternative yes or no answer determines the next step in the dichotomous key.
Identify the mammal on the right in the picture. Circle each answer.
A dichotomous key can be shown as a
_________________________________
with characteristics on each branch. These
questions start with
1.
Is it ___________________?
2.
Does it have ________________?
3.
Radial _____________________?
4.
___________________ symmetry?
These characteristics classify animals.
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.
Binomial Nomenclature
Your newly discovered organism now needs a name. Carolus ______________________ developed the
______________________ system so every species has a unique two part scientific name. The rules are:
1. The scientific name consists of the ___________________________.
2. Both words are _________________ or underlined.
3. Genus is always ___________________.
4. species is always _________________________
5. Both name are in __________________.
6. The species name must be ___________________ in the same Genus.
For example, _____________________________ or ________________________
Why use scientific names? _____________________ names of an organism are ___________________
in every ___________________. Durian’s scientific name is Durio zibethinus
Dichotomous Keys
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.
4. Biological species concept – organisms can successfully breed and produce fertile offspring. This
widely used concept only works for living, sexually reproducing organisms.
5. Morphological species concept – comparing the measurements and physical descriptions. Often
used for plants or asexually reproducing organisms.
6. Phylogenetic species concept – looks for evolutionary relationships between organisms. Usually
based on DNA studies or fossil evidence.
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. 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.
Identify the mammal on the right in the picture. Circle each answer.
A dichotomous key can be shown as a branching tree diagram with characteristics on each branch. The
questions start with
5. Is it multicellular?
6. Does it have tissues?
7. Radial symmetry?
8. Bilateral symmetry?
These characteristics classify animals.
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.
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:
7. The scientific name consists of the genus and species.
8. Both words are italicized or underlined.
9. Genus is always capitalized.
10. species is always lower-case.
11. Both name are in Latin.
12. The species name must be unique in the same Genus.
For example, Ursus arctos or Homo sapiens
Why use scientific names? Common names of an organism are different in every language. Durian’s
scientific name is Durio zibethinus