When students are taking a biology class, they may learn about something called a "dichotomous key." This helpful tool that scientists create is used to assist people in recognizing organisms and objects. If an object or organism is unknown, users can utilize the tool to determine what exactly they are.

A dichotomous key is important because of the sheer amount of species on Earth. Currently, there are 1.5 million species on the planet, and there may be up to 100 million more than have been undiscovered.

Learning how a dichotomous key in biology works and figuring out where to find a dichotomous key generator will help students to make their own and aid others in important identifications in nature.

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How to Use a Dichotomous Key in Biology

A dichotomous key will consist of a series of questions, usually about a specific species. When a user answers one question, the key helps the user decide what question to ask next to finally arrive at an answer. There will always be two answers to a question, making it easier for the user to get to the final answer and identify the unknown organism or object. Many will have “yes” or “no” as the two answers.

If the key is about a certain species, the scientific name for the species will be used. This is because the common names used for species usually refer to various species that simply look similar to one another.

For example, a moth and a butterfly look similar, but the fact is that they are completely different. They are both part of the scientific order Lepidoptera, but they serve different functions in the world and have many dissimilar traits. Having the scientific name will clear up any confusion.

Who Uses Dichotomous Keys?

Anyone can use a dichotomous key calculator to classify an object. They are meant for nonexperts to be able to come up with the answers on their own. For example, only an expert would know that a certain tree has a number of branches in a specific order. A dichotomous key could ask users questions that help guide them to answers and provides them with useful information.

The name “dichotomous” is Greek: “di” means “two,” and “tome” means “cutting instrument.” There are two answers to every question, and each answer cuts down the possibilities of another answer.

Field guides will often use dichotomous keys to identify a certain plant or animal. However, they can be utilized for any object. When practicing making a dichotomous key calculator, students will use simple objects like pencils or even a classmate as their first key.

The Different Types of Dichotomous Keys

There are a few different ways to display information in a dichotomous key calculator.

  • The first is a linked style, where questions are laid out in a list. Each answer guides the user to which question he should ask next, and the user needs to find the right question to identify the object.

  • There’s also a nested-style dichotomous key calculator, where the next question looks nested under the answer leading to the question. It will appear as an indentation; each question after the first one will be further indented to distinguish it from the rest.

  • A branching or tree dichotomous key involves laying out each object’s characteristics in a style that looks like a tree of life or a flow chart. Each question will be on a new branch of the tree, and each answer will appear on a sub-branch.

  • In a computer program dichotomous key, the user will determine the identity of the unknown object by answering a series of questions that are "either-or."

How to Make a Dichotomous Key in Biology for Students

Making a dichotomous key is easy. All students need is a dichotomous key maker template and some directions to get started. The first step is to gather materials like poster board, pencils and a ruler to draw the boxes containing the questions, answers and connecting lines. Students can start off with a simple exercise, such as identifying a classmate.

The first question could be, “Is the student a girl or a boy?” with the two answers being “girl” and “boy.” It’s best to start out with generalities and then get more specific. For example, if the answer is a student, the questions could be about eye and hair color, height and age.

Once students get comfortable with creating a simple dichotomous key, they can pick up a field guidebook and choose a leaf from a tree or a petal from a flower, for example, to come up with their nature dichotomous key. They can identify the tree or flower from the field guide and come up with questions to guide the user to the answer.

Why a Dichotomous Key Is Used in Schools

Dichotomous keys are typically used in elementary or middle schools since it helps young students to grasp harder scientific concepts. Making a dichotomous key is also a fun activity for younger kids. These students can go outside, take a leaf off a tree or photograph it, research it using their field guides and quiz their classmates. They can feel empowered and like real scientists when they discover the answers and figure out what an unknown organism or object might be.

Since dichotomous keys can also be created on a computer, it presents an opportunity for teachers to familiarize younger students with technology. Making the key can be an in-class or at-home assignment that gets students excited about science. It fosters their curiosity and encourages them to explore the world around them.

How to Make a Dichotomous Key in Biology for Teachers

Teachers can also develop dichotomous keys to show to their students before the students venture out on their own. A teacher could locate 10 pictures of various animals and plants that have distinct characteristics.

The teacher can put the pictures up on a smart board or a blackboard and then ask the students to pick out different physical traits of the animals or plants. For example, if there is a picture of a dog, the students would have to say, “This animal has a long snout” instead of “This animal is a domesticated.”

The teacher can then create a simple dichotomous key – like a branch model – and then ask students to collect 10 pictures and do the same. Students can check each other’s work to ensure they are doing it correctly.

Where to Find a Dichotomous Key Generator

There are places online where students and teachers can generate their own dichotomous keys. One site, Creately, allows users to create and edit dichotomous keys with themed color palettes and styles. The keys can be exported to PDFs or used in Word documents and PowerPoint presentations.

Another site, SmartDraw, lets students and teachers produce a decision tree. It includes dozens of tree templates and lets teams work on the tree together.

Dichotomous keys are important learning tools for biology students. With them, the students can grasp complicated concepts and feel like experts in the field.

Things Needed

  • Pen and paper or a computer

About the Author

Kylie Ora Lobell is a freelance writer in Los Angeles. She has written about education for topics for LegalZoom, Jewish Journal of Los Angeles, Cornerstone and WeWork.