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TX: Dichotomous Key Lesson

Fork in the Road 


Have you ever read “Choose Your Own Adventure” books? These books allowed you to make choices about how the story would go. You would choose between two different options and it would tell you which page to go to continue reading your adventure.

You may be wondering why we are talking about books in a biology class. Scientists use dichotomous keys to identify organisms, much like a “Choose Your Own Adventure” book.

"Dichotomous" means to branch into two. Dichotomous keys present two choices at each step in identifying organisms, much like a fork in the road.

Each road takes you on a new path!

The Key

Watch the presentation below to learn more about the key. 

Let's take a look at the following example:

Key Example, description below

See description of image Links to an external site.

Rules for Using Dichotomous Keys

It is very important that you remember the rules!

  1. Read both parts of each couplet carefully. 
  2. If you do not understand a term used, look it up!
  3. If you are asked to measure something, do not guess at the measurement, use the proper tool.
  4. If you are unsure which choice to make, follow both paths and see where each takes you; inevitably one will not fit. 
  5. Write down the order of the steps you took (couplet 1b, to 4b, to 6a)
  6. Double-check your work!

Let's Watch This In Action!

 

Dichotomous Key Challenge and Before You Go

Practice Time! Use the knowledge you learned from the lesson to complete the practice activities below.

Zetas are an imaginary genus of extraterrestrials. Six species of the Zeta genus exist. Use the Zetas to practice using a dichotomous key.

Directions: Examine the alien Zeta species below. Use the key that follows to identify them to species. Write the scientific name for each Zeta species on a piece of paper.

Zeta genus example

Answer Key Links to an external site.

Before You Go - You Need To Know

 

The following key points are from the explore section of the lesson. You must know the following information before moving to the next lesson. This is just a summary of the key points.

  1. What is a dichotomous key?
    • It is a way to determine the identity of living organisms by going through two choices.
  2. What does the word “dichotomous” mean?
    • To branch into two
  3. What are the rules for using a dichotomous key?
    • Read the choices carefully.
    • Look up any words you do not understand.
    • Measure exactly.
    • Write down the steps you took.
    • Double-check your work.

IMAGES CREATED BY GAVS (FREEPIK)