What do you use a dichotomous key for

There are two kinds of descriptions that might be presented to the user of a dichotomous key: qualitative and quantitative descriptions. Qualitative descriptions concern the physical attributes, or qualities , of the item being classified. Knowing the difference between these two types of descriptions can be immensely beneficial for creators and users of dichotomous keys. There are two ways to set up a dichotomous key. One way is to present the two choices together, and the other way is to group by relationships.

When the dichotomous key is set up by presenting the two choices together, it is easy to distinguish between them. 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.

Energy Flow 3. Carbon Cycling 4. Climate Change 5: Evolution 1. Evolution Evidence 2. Natural Selection 3. Classification 4. Cladistics 6: Human Physiology 1. Digestion 2. The Blood System 3. Disease Defences 4. Gas Exchange 5. Homeostasis Higher Level 7: Nucleic Acids 1. DNA Structure 2. Transcription 3. Translation 8: Metabolism 1. Metabolism 2. Cell Respiration 3. Photosynthesis 9: Plant Biology 1. To use a dichotomous key, one must be able to make accurate observations and follow directions carefully.

Focus Questions: How can you identify an unknown organism? What types of characteristics can be used to identify an organism? How do you use a dichotomous key and why is a dichotomous key important?

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.