Introduction
The objectives for this week's homework are to introduce you to the dichotomous key, or a type of "map" that will allow you to determine the identity of living things. Two weeks ago we learned how living things began to be universally identified using the binomial nomenclature system devised by Linnaeus -- which is a marvel, except if you live in the depths of an Amazon jungle and want to describe a fantastic little frog that you've found. What to name it? Does it have a name already? Does anyone else in the world know that it exists?
To help answer these questions, scientists have developed many, many keys for the use of others to use in identifying living things.
The Task
Doing this week's homework, you will learn:
- What a dichotomous key is,
- How to use one, and
- How to make one!
The Process
The format for this homework is the same as our usual format - daily assignments and asterisked items that are to be turned in during class.
Monday:
Download 2 copies of the Fish Sorting Activity sheet here.
Using the first copy, cut the fish apart and glue them to another sheet of paper* using an organizational scheme that makes sense to you. For example, you may want to group them according to ratio of body length to body width, or by number of visible fins etc. Whatever you choose, write your organization scheme at the bottom of the page.
With the second copy, use the key at the bottom of the page to identify each fish*. Write the name of each fish just below it.
You have just used a dichotomous key. The fish key used visible characteristics to separate the larger group of fish from one another until each individual fish could be identified. This was easy!
Let's try another key. Download, (one copy this time!) the Alaska Winter Tree Key. Now, go outside and cut off a small branch from a tree (taller than four feet - don't mistakenly get a shrub!)
Use the key to identify what you've cut off*. Since we don't have a large variety of trees, this key is also not very complicated.
Tuesday:
We're getting a bit more complex. On a separate piece of paper, number from 1-20. Then, go here and identify the Pamishans!*
You may notice that, in using dichotomous keys, you need to be very observant! One stray spike somewhere can make all the difference!
We'll now apply your observational skills to yet another key - this is one of real living things however! At this website, read the introduction (a review) and do Exercise 3. Using Mozilla Firefox, I noticed that all the images don't show up. Perhaps they do in Internet Explorer.
Write down your answers* on a separate piece of paper numbered 1-16. (Obviously, if you can't see an image, you can't name the tree...)
Wednesday:
More key practice! Go to this website from Australia. Read the introduction and go ahead, laugh!! These are NOT animals with which we are familiar, but they are ones I trust you know about. Follow the instructions on this page to see how the "couplet" approach (use of "choose a. or b." sets of questions) is used to identify each animal.
Now, go to the dichotomous key outline and see the whole key written out. I want you to understand that each key uses sets of two questions to narrow the possibilities. And your understanding of this is impotant because, today, you will create your own key and share it with the class!
Select ten "things" (Your choice - You can use ten things you pull out of your junk drawer at home, ten bolts/screws etc. from the workshop, ten animals, ten pieces of clothing or a completely random assortment of ten things.) Use the information on this page to help you create your own key.*
Thursday:
Bring to class: Each asterisked assignment. For the key that you created, bring a list of the ten things, the key itself and the answers! We're going to work out each others' keys! (If you will not be in class, be sure to email me these things so we can still use your key!)
Conclusion
I expect that you are now very in tune with how to use a dichotomous key. You've seen them, you've used them and you've made one. We'll extend this activity in the classroom! Well done.
⇐ Go back to the Order and Design Homework Page.