Dichotomous Key Quiz

1. Butterflies usually are identified by the colors and patterns on their wings. Butterflies have four wings: The two wings near the butterfly’s head are “forewings” while the wings near the butterfly’s tail are “hindwings.” You can use the following dichotomous key to identify four common butterfly species in North America.
   
   
   Based on the key, what species of butterfly is shown?
   Click on the rectangle around the correct scientific name that you think is correct.

Answer explanation

To identify an organism using a dichotomous key, compare the organism’s traits to the first pair of descriptive statements on the key. Follow the directions after each matching statement until you get to the organism’s identity. The points on the hindwings identify the butterfly as a swallowtail butterfly—it is either Papilio glaucus or Papilio polyxenes. The wings are mainly black, so the butterfly is Papilio polyxenes (common black swallowtail).

Tags

NGSS.MS-LS4-2

Based on the same dichotomous key, what is the butterfly shown​ ​ ? (a)  

• Danaus plexippus
• Papilio polyxenes
• Papilio glaucus

Answer explanation

The pictured butterfly has rounded hindwings, so it is either Danaus plexippus or Colias philodice. The wings are yellow with black edges, so the butterfly is Colias philodice, known as the common sulphur butterfly.

1. Students are using the pictured dichotomous key for leaves below to help identify native trees. Which of the following leaves is classified as Holly?

   
   

• 
• 
• 
• 

Answer explanation

Characteristics of leaves such as color, shape, leaf size, leaf arrangement, and other characteristics can be used to classify trees using a dichotomous key of known species. Characteristics can be systematically narrowed down through a series of choices to eventually match the sample to the known species.

Tags

NGSS.MS-LS4-2

Suppose you were making a dichotomous key to identify the three types of leaves shown. Which of the following traits could you use to classify these leaves into separate groups?

• Presence or absence of veins in the leaves.

• Presence or absence of stems.

• How leaves are arranged on branches.

• Size of leaves.

Answer explanation

To be useful in a dichotomous key, a trait should separate organisms into different groups. All of the pictured leaves are approximately the same size, all have veins, and all have stems, so these traits do not separate the samples into different groups. What does make these leaves different is how they are arranged on the branch. Therefore, C is correct: how the leaves are arranged on the branches would be the best way to separate the leaves.

In 2-3 sentences, describe how characteristics of leaves can be used to classify trees with a dichotomous key.

You may copy and paste this sentence stem, if needed: The characteristics of leaves can be used to classify trees by _______.