Dichotomous Key
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5 responses to “Dichotomous Key”
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Hi Sable,
I see where you are going with this key, but I do see a problem with it. Plant 4 has stems – you can make a stem out in the top left photo. As well, the leaves have petioles – and petioles attach leaves to stems.
Your first couplet – which should be labeled A and A’ since they relate very closely to each other (and not A and B) – is nice and descriptive. A’ needs to point directly to another couplet, however, if it’s not going to resolve to a plant. The descriptors are correct.
Your third couplet – which would be labeled C and C’ – is very good. Descriptive, precise, and points to a logical conclusion. It is quite correct, btw.
Since C *IS* correct, but Plants 2, 3 and 4 have stems, is there another, single, characteristic that obviously comes to mind? THAT would be your B and B’ couplet.
Once you resolve these, go ahead and resubmit (you can reply, or modify your original post).
If you get stuck, go ahead and email me. Plant 4 is a bit subtle, but once you see it, it will be obvious.
Good job!
Steph -
Here are the changes I made with your suggestions!
I am curious if A and A’ are good differentiators because they are not related and I was under the impression that they needed to be. In the examples they are often opposites like flowers or no flowers etc. -
You bring up a very valid point, and are correct – they DO need to be related (they are, essentially, opposite conditions, e.g., one has glitter, the other lacks glitter). One way to keep A and A’ more related is to focus on pairing the organ in question. For instance: One has needles, the other has flat leaves (since both are leaves). Or, one has cones, the other lacks cones – simple, and still very precise. Your B couplet is almost right, and your C couplet is perfect.
Your unresolved descriptor in the couplets (i.e., A’, B’, etc.) still needs to point to the next appropriate couplet (e.g. Q’ -> Y, Y’ -> BB, etc.). Otherwise, the reader may not know where to go. Make each line obvious where the reader should look next.
With THAT in mind, give it one more try.
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How about this?
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Very good!
It’s okay to keep the descriptors simple – “Plant has needles”, “Flower with purple petals”, etc. And it’s ok just to point to the couplet – “Plant lacks needles …… B” rather than “See couplet B”. Otherwise, it’s fine!
Thanks for resubmitting!
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