Which statement best defines a dichotomous key?

• A. Identify organisms by a series of unpaired questions
• B. Predict weather patterns
• C. Analyze DNA sequences
• D. Identify organisms by a series of paired statements used to classify them

Answer: (D)

A dichotomous key is a step-by-step tool for identifying organisms by making a sequence of paired choices. At each step you compare a visible feature and pick one of two contrasting statements that best describes the organism. The path you follow from one pair to the next narrows possibilities until you reach a single identification. This emphasis on paired statements used to classify organisms is what makes the definition fit best. Other options describe different activities—predicting weather, analyzing DNA sequences, or using unpaired questions—that don’t capture the identification process of alternating between two clear choices to classify organisms.