DICHOTOMOUS KEYS How do we know what something

DICHOTOMOUS KEYS

How do we know what something is? ■ Living things are organized in a system called taxonomy. ■ We use defining traits or characteristics to determine how to split up the organisms. – Diet – Movement – Habitat – Physical characteristics such as color, shape, or size – The ability to reproduce with one another

§ Organisms are grouped together or classified based on common traits. As you move through the levels of taxonomy the characteristics get more specific and the groups generally get smaller. �Kingdom �Phylum �Class �Order �Family �Genus �Species

Dichotomous Keys ■ A dichotomous key is a tool that allows the user to determine the identity of items in the natural world based on the items characteristics ■ "Dichotomous" means “divided into two parts” Greek origin ■ Dichotomous keys always give two distinct choices in each step, often they are opposites – Black/white; good/evil; pointed/rounded

HOW TO USE A DICHOTOMOUS KEY Here are creatures we don’t know! Lets choose one

Choose only 1 creature at a time.

Read the first set of choices (Steps 1 a and 1 b). Decide which statement is true. 1 b is true

Then follow the directions after that step. G O T O P E ST

At step 5 you make another dichotomous choice. GO 5 a is true TO STE P 6!

Continue working through the steps and choices until you come to one that gives you the creatures name. 6 a. The creature has one antennae Go to Step 7. C

Lets try some insects! 1. a. wings covered by an exoskeleton – go to step 2 b. wings freely observed – Go to step 3 2. a. body has a round shape ………. ladybug, a red beetle with black spots b. body has an elongated shape ………. grasshopper, a green insect that hops 1 2 Dragonfly Grasshoppe r 3 4 Housefly Ladybug 3. a. wings point out from the side of the body ………. dragonfly, an insect that is 10 - 15 cm long and lives in marshes b. wings point to the posterior of the body ………. housefly, a flying insect with red eyes and an annoying buzz

WHAT IF I NEED TO § Use constant characteristics rather than variable MAKE A KEY? ones. (Flowers change with the seasons) § Use measurements rather than terms like "large" and "small". § Make the choice a positive one § Something "is" instead of "is not". § If possible, start both choices of a pair with the same word or item. § the body is “round” vs the body is “square” § Finish the dichotomous key with a full description of the organism.

Dichotomou s keys can also be expressed as a flow chart.