Engage: The Crime



One dark and stormy evening, a group of people was gathered at an enormous mansion owned by William DaVictim. A massive storm approached and, as the thunder roared, the power went out. During the 10 minutes of extreme darkness, a blood-curdling scream rang out. When the lights came on, Mr. DaVictim was found dead in a pool of his own blood. The police came immediately and spoke with each individual. Move on to the next section to discover what their statements to police revealed and to see if you can find the person who committed the crime!

Explore: Solving the Crime

To determine who committed this crime, you will need the information gathered from detectives on the scene. Each potential suspect was thoroughly interviewed. Use RM1: Gathering Evidence to record clues as you watch each interview summary.

Who do you think committed this horrific crime? Use the clues you have gathered and the key below to find out!



Explain: Dichotomous Keys

So, yes, Molly Daggers did it. We found the culprit, and now she can be put to justice! 

What's amazing is that you just learned a bit of science while you cracked that fictional case. The key you used to determine who the criminal was is called a dichotomous key. A dichotomous key is like a puzzle with steps that are followed. These are generally used in science to classify plants or animals based on characteristics. Let's take a look at how this works. Watch the video below to find out more.


Elaborate: Scientific Application

In the world past high school, scientists use dichotomous keys to identify plants and animals. However, dichotomous keys, which generally contain a pair of statements, are not the only type of key that scientists use. Some keys consists of pictures, and you choose which one looks most like your specimens.

Look at the three leaf specimens in the image below. 

three leaf specimens

Now, click the hand lens to visit the Texas A&M Forest Service ID by Leaf website. Determine the species of each type of tree specimen.

Teacher Notes

This resource is a compilation of text, videos, and other elements to create a scaffolded 5E learning experience for students. This is meant for Tier I instruction under the Response to Intervention (RtI) model for grade 7 science TEKS (7)(11)(A), specifically, dichotomous keys.

Be sure to check for prerequisite knowledge and skills as well as differentiation needs by reviewing the entire resource and the related items before assigning it to or working through it with your students.

This resource can be used for instruction in a variety of ways.

• Use with a single computer and projector; this can be delivered in a traditional classroom.
• Use with a combination of individual student computers and teacher computer and projector (in either a computer lab or other 1:1 environment).
• Assign the resource to students as work to do outside of the school day as part of a "flipped classroom" to allow application, practice, and additional support during the school day.
• Use with students as tutorials.
• Share with parents to inform them about what their child is learning in school.
• Use with students who are unable to participate in the traditional classroom environment.

Students are intrigued by the setup of a murder-mystery experience. This is meant to heighten students' curiosity and engagement. By getting students engaged in something that seems like entertainment, they may make better connections to the content.

Students view a video containing the results of the suspects' interviews with police. Students use this information and a dichotomous key to determine who is the perpetrator of the crime.

Classroom Option

Insert another dichotomous key experience for students who seem to struggle with the murder-mystery key. Multiple experiences that seem nonscientific will help students better understand how they work. Once students understand how these keys work, then they can apply their understanding to a more scientific use of the tool.

The Explain phase reveals to students that they were using a dichotomous key for the murder mystery and then illustrates a more scientific application for the student using a video. While dichotomous keys are generally used for plants and animals, they could conceivably be used for rocks, biomes, and other scientific areas.

This is an important place to mention the specific verb that's used in the 7(11)(A). The student expectation reads, "The student is expected to examine organisms or their structures such as insects or leaves and use dichotomous keys for identification." The key word here is use. Students are expected to use a given dichotomous key to come to a given conclusion. Given the specific verb in the student expectation, having students create their own dichotomous keys may not be a valuable use of class time and may actually steal time away from practicing the skill students are expected to master.

Classroom Option

Allowing students other experiences with dichotomous keys for plants and animals is beneficial here. The student expectation uses the term "such as," meaning that it is wise to expose students to dichotomous keys for organisms other than insects and plants. Varying the format of key is helpful for students as well so that they become comfortable with the different types of keys (flow chart, table, etc.).

The Elaborate phase gives students an opportunity to practice using a key that uses photos. There is no chart, and the experience is largely visual. This activity more appropriately mimics how scientists determine species in the field. (The leaf exercise answers are: Sassafras, Japanese maple, and Douglas fir.)