A dichotomous key is a method for identifying and classifying objects, where each feature selected to help identification requires a choice between two alternatives.
Choose a definable difference to separate them into two groups. For example, the difference can't be "big or small" because these choices are not well enough defined, but could be "under cm in height "and " cm or over in height". Using this key, a visitor to the classroom could quickly work out which child was James. Similarly, the visitor would be able to work out the name of the blond, ear-ringed boy with the jumper.
Note: Some features may not be as useful as others. What happens if James gets hot and takes off his jumper? And what if Scott peroxides his hair? Using these characteristics in this situation, James, Scott and Michael share many features in common, which may be very different from the others in the group. However, relationships between various characteristics are not emphasized.
When the dichotomous key is grouped by relationships, the choices are separated, yet it is easy to see the relationships between them. While this method may prove to be more difficult to construct, many users prefer it because it gives them more information. Blackline Master 1 gives students instructions on how to use a dichotomous key in general. In this activity you will find two styles of dichotomous keys download Blackline Masters 2 and 3 and seashell pictures used in the keys Blackline Master 4, pages Pick one of the dichotomous key worksheets; both reflect the same dichotomous process and use the same seashell pictures.
Links to downloading the Blackline Masters can be found below. Duplicate as many keys and sets of seashell pictures as necessary for each student or student group. It is suggested that if you use this activity many times, you should laminate the pictures of the shells and then cut them apart as sets for future use. If you do not lighten the density, the images will be difficult to see.
If student is a visual learner use Blackline Master 3. Description: An excellent web-based activity on the construction and use of a dichotomous key that also describes the use of a dichotomous key in the field and provides a key for prairie plants.
Pictures can be projected on a smart board or overhead projector, or magnets can be placed on the back of pictures for placement on the blackboard. Pictures should be diverse and have evident easily seen characteristics.
The instructor will ask the students to observe traits of the displayed organisms. Dichotomous keys are based on observations, so the instructor should encourage students to use observable characteristics, rather than behaviors. Students will then use the pictures to model the process of creating a dichotomous key.
Download Attachment 1. Download Worksheet 1. Download Lesson Plan. This type of key is not hard to use, but makes more sense when students undertake the process of making one before using it. The instructor will model the process before students begin work on their own keys. After the demonstration, students will first make a Branching Key using a picture of an organism of their choice. Once the Branching Key is completed, students will convert it into a written dichotomous key. The end product will be a poster displaying the student pictures, along with their written dichotomous keys.
After modeling the process, direct students to take out the ten pictures that they collected for their project.
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