Lesson 2 - Dichotomous Key

• At what levels is life organized?

  From cells to biosphere
• How do biologists classify organisms?

  By similarities in their structures
• What does the modern classification system use to group organisms?

  A series of levels
• What is the relationship between shared classification levels and characteristics?

  The more levels shared, the more characteristics in common
• What is a dichotomous key?

  A tool for identifying items based on characteristics
• What does the term "dichotomous" mean?


  Divided into two parts
• What do dichotomous keys provide at each step?

  Two distinct choices
• What are couplets in a taxonomic key?


  Pairs of contrasting statements
• What is a lead in a couplet?


  Statements making up a couplet
• What is fixed in a dichotomous key?

  The sequence and structure of identification steps
• What are diagnostic keys focused on?


  Making identification easier
• What do synoptic keys aim to reflect?


  The scientific classifications of organisms
• What are the rules for making taxonomic keys?

  1. Same lead word for each couplet
  2. No same starting words for consecutive couplets
  3. Contradictory statements in leads
  4. Use positive statements
  5. Avoid overlapping ranges or vague generalities
  6. Use observable or macroscopic features
  7. Avoid geographical location as sole separation
  8. Show group relationships
• How can a dichotomous key be expressed?

  In a diagram form
• What should the lead word of each couplet be?

  The same for both leads
• What should consecutive couplets not begin with?

  The same word/s
• What should leads express in a dichotomous key?

  Contradictory statements
• What type of statements should be used in leads?

  Positive statements
• What should be avoided in couplets?

  Overlapping ranges or vague generalities
• What type of features should be used in taxonomic keys?

  Observable or macroscopic features
• What should not be used as a sole separation character?

  Geographical location
• What should a dichotomous key show?

  Group relationships