constructing a dichotomous key. what is a dichotomous key? a system of identifying objects or...
TRANSCRIPT
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Constructing a Dichotomous Key
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What is a Dichotomous Key?
• A system of identifying objects or organisms in which a succession of paired choices leads progressively to identification of the object (the only remaining correct choice.)
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Using a Dichotomous Key
• Study the organisms that will be classified. Choose one
• Read the first set of choices in the dichotomous key
• Decide which characteristic the organism has• Follow the numbered items in the key and
name the organism
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Finch Identification
1. a. The beak is relatively long and slender. Certhdea sp.
b. The beak is relatively stout and heavy. Go to set 2
2. a. The bottom surface of the lower bill is flat and straight.
Geospiza sp.
b. The bottom surface of the lower bill has a bend Go to set 3
3. a. The lower edge of the upper bill has a distinct bend.
Camarhynchus sp.
b. The lower edge of the upper bill is mostly flat. Platyspiza sp.
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Seatwork
• Complete the Using a Dichotomous Key assignment
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Constructing a Dichotomous Key
• The first step is to look at the group of objects or organisms and separate them into two groups based on a single distinguishing characteristic.
• Then continue to separate each of the groups until each object has its own separate set of characteristics.
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An Example
• As an example, we could construct a key using the following stationary supplies taken from a student's pencil case.
• pen, highlighter, pencil sharpener, paper clip
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A Spider Key
• Some students find it easier to arrange their information in a spider key before setting it up in the traditional dichotomous key format.
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A Traditional Dichotomous Key
• The same information presented in a traditional dichotomous key format would look like this:
1. a. long tubular objects………………go to #2 b. short, non-tubular objects ……. ..go to #42. a. constructed from plastic …………go to #3 b. not constructed of plastic ……….pencil3. a. green and grey ………………......highlighter b. blue and clear …………………….pen4. a. black and silver …………………..pencil sharpener b. silver ……………………………….paper clip
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Homework• Create a dichotomous key for the insects on page 26 #16• Number them from 1 – 7 starting on the top row left to right (1 – 3) • Second row left to right (4 – 7 )