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What keys do you know about?
EPISD Middle School Science Standards Based Curriculum 2015-2016
Dichotomous Keys are:
•hierarchical•mutually exclusive• exhaustive
EPISD Middle School Science Standards Based Curriculum 2015-2016
Mutually Exclusive
• There are only two choices • If it is in one group, it cannot be in another
• Example:– Organism has a hard exoskeleton– Organism has a hard endoskeleton
The organism cannot have both a hard exoskeleton and a hard endoskeleton.
EPISD Middle School Science Standards Based Curriculum 2015-2016
Hierarchical
EPISD Middle School Science Standards Based Curriculum 2015-2016
Exhaustive
• Includes ALL possible variation combinations• It has already been broken down to its
smallest group
• What happens when a new species is discovered or bred?
EPISD Middle School Science Standards Based Curriculum 2015-2016
Example of how to build your own Dichotomous key using office supplies
Uses electricity Does not use electricity
EPISD Middle School Science Standards Based Curriculum 2015-2016
Dichotomous Key*ALWAYS start at question 1
1. a. uses electricity………...................................go to 2 b. does not use electricity………………………..….go to 32. a. has letter, symbols, and number keys……..keyboard b. has number and symbol keys ………………….calculator3. a. long, slender objects………………………………..go to 4 b. not long, slender objects………………………….go to ?4. a. made from plastic…………………………………….go to? b. made from something other then plastic….go to?
EPISD Middle School Science Standards Based Curriculum 2015-2016
EPISD Middle School Science Standards Based Curriculum 2015-2016
Example of a Dichotomous key for insects
Image taken from http://www.rivercenter.uga.edu/education/watersheds2006/gps.htm
Is it an Ant or a Grasshopper? 1. a. has six legs……………………………….….go to 2
b. does not have six legs…………………..go to 4 2. a. has an antennae…………………………..go to 3
b. does not have an antennae…………..go to 53. a. large hind legs for hopping…….grasshopper
b. no large hind legs for hopping………….Ant
EPISD Middle School Science Standards Based Curriculum 2015-2016
Common Names vs. Scientific Namesmountain lion Felis concolor
gray wolf Canis lupus
humans Homo sapiens
saguaro Cactus Carnegiea gigantea
dog Canis familiaris
EPISD Middle School Science Standards Based Curriculum 2015-2016