Video Transcript
A student writes, “A dichotomous key is a series of descriptions grouped into threes
that help identify an organism from its characteristics.” What is incorrect about this statement? (A) Dichotomous keys identify organisms based on their genetics, not their
characteristics. (B) Dichotomous keys are always a series of pictures, not descriptions. (C) Dichotomous keys have descriptions arranged in pairs, not threes. (D) Nothing is incorrect about this statement.
This question is asking us about dichotomous keys. Let’s learn what dichotomous keys are and how they work. Then, we will return to this question to identify what’s incorrect about the provided
statement.
A dichotomous key is a tool to help identify organisms based on their
characteristics. There are two forms: a list style and a chart style dichotomous key. Shown here is a chart style dichotomous key, and on the left is a flower we need to
identify as specimen A, B, or C.
Dichotomous keys ask us to identify the best description for a particular
characteristic in pairs. We start at the top and look at the first binary question. Are the petals pink or are they white? They’re pink, so then we follow the branch down to the left. This rules out specimen C. The next question asks if the flower has leaves or not. Our flower has no leaves, so that rules out specimen A, and we follow the branch on
the right. This means our specimen is specimen B.
You may notice that the chart style dichotomous key looks similar to an evolutionary
tree, but it’s important not to confuse the two. A dichotomous key is not used to determine evolutionary relationships but is used for
distinguishing specimens from one another to properly identify them. It does this by asking us to choose the best description for different
characteristics. And these are arranged in pairs, not in threes as indicated in the provided
statement. Therefore, the option that best describes what’s incorrect about this provided
statement is given by answer choice (C). Dichotomous keys have descriptions arranged in pairs, not threes.
