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Why have a system of classification?. To assign each unique organism its own unique name To show evolutionary relationships between present day and past organisms. Linnaeus System of Classification.

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why have a system of classification
Why have a system of classification?
  • To assign each unique organism its own unique name
  • To show evolutionary relationships between present day and past organisms.
linnaeus system of classification
Linnaeus System of Classification
  • Carl Linne (Linnaeus) moved past simple habitat categories of Land, Water, and Air dweller of aristotle.
  • Linnaeus used morphology to group organisms into categories (Taxa) from the broadest Kingdoms to the most specific species
  • The Linnaeus system has 7 hierarchical levelsthat move from larger to smaller, more specific groups
    • Kingdom, Phylum, Class, Order, Family, Genus, and Species
  • Each unique species is identified by a binomial (two part) name consisting of its Genus and species names. For example humans are

Homo sapiens

Genus species

dichotomous key
Dichotomous Key

di·chot·o·mous (adj.) Divided or dividing into two parts or classifications.

Suppose you have four insects a ladybug, a housefly, a dragonfly and a grasshopper. After studying the insects, you might use wing covering, body shape, and where the wings point towards. To begin the key, you could start separating the four insects based on wing covering - "wings covered by exoskeleton" vs. "wings not covered by exoskeleton." A dichotomous key for the organisms above is shown on the next page.

dichotomous key1
Dichotomous Key

The first step in the key will be organized the following way:

1. a. wings covered by an exoskeleton

b. wings not covered by an exoskeleton

Next, the statements need to lead the observer to the next step to narrow the identification further:

1. a. wings covered by an exoskeleton ………go to step 2

b. wings not covered by an exoskeleton ……….go to step 3

Step 2 needs to consist of a pair of statements that will allow for the identification of the ladybug and the grasshopper:

2. a. body has a round shape ……….ladybug

b. body has an elongated shape ……….grasshopper

Step 3 needs to consist of a pair of statements that will allow for the identification of the housefly and dragonfly:

3. a. wings point out from the side of the body ……….dragonfly

b. wings point to the posterior of the body ……….housefly

Notice that there were four organisms to be identified and it only took three steps. There should be one less step than the total number of organisms to be identified in your dichotomous key.

other dichotomous key sites
Other Dichotomous Key sites

http://www.biologycorner.com/worksheets/dichoto.html