1-Lesson 2 - Domains and Kingdoms Learning goals - understand concepts related to taxonomy and phylogeny in classifying different organisms Success criteria - explain the fundamental principles of taxonomy and phylogeny by defining concepts of taxonomic rank and relationship, such as genus, species, and taxon; B2.4 create and apply a dichotomous key to identify and classify organisms from each of the kingdoms B3.1, B2.4 INSTRUCTIONS: 1. At the end of this lesson, complete the 'CYU - Using a Dichotomous Key' activities given to check your understanding of this concept. As you learned in the previous lesson, we can classify living organisms into the eight ranks shown in the diagram above. Examining diversity at the species level is too complex therefore biologists analyse similarities and differences at higher taxonomic ranks – e.g. kingdoms or domains ● Structural diversity: a type of biological diversity that is exhibited in the variety of structural forms in living things, from internal cell structure to body morphology Until the 1800s, the highest category was thought to be the kingdom, with only two kingdoms identified - plants and animals. The number of kingdoms have increased since then, to include fungi, protists, bacteria, and archaea. We will be examining each kingdom in detail in the next lesson, but there are three important things to remember as we delve into this topic: 1. There are two main cell types significant for classification at upper ranks 2. The study of cell types and genes has led scientists to add a rank higher than kingdom – i.e. the domain 3. It is important to understand how domains and kingdoms are connected in their evolutionary history Note – if an organism is made of one cell, they are called unicellular vs. multiple cells called multicellular. 2) There are three domains: bacteria, archaea, and eukarya ● There are six major categories in the classification of living and extinct organisms within the three domains - these correspond to the six kingdoms in the classification system. 3) Investigating fundamental differences in cell type/structure, cell wall material, no. of cells (unicellular vs. multicellular), methods of reproduction, and how different living organisms obtain nutrition allows to categorize each species into different kingdoms. DICHOTOMOUS KEYS Biologists often use dichotomous keys to classify unknown organisms/species by narrowing down the identification one step at a time. For example, if you were hiking in a forest and saw the following birds, you could observe differences in their physical appearances to try and identify what species each bird belongs to. The first three birds have elongated bills compared to the last two - this would be the first step in categorizing the groups of birds. Next, out of the birds with the elongated bills (i.e. the first three), one has a strongly curved bill while the other two have straight bills - this step allows the group of three birds to be narrowed down further. This method of classifying the group of birds step-by-step allows you to eventually arrive at the smallest available classification unit. Like in the example above, at each step of a dichotomous key, the use must choose between two defining statements. Each alternative leads to a result or another choice. Eventually, the key ends with the classification of the organism into a specific taxonomic level. Most often, you would see these dichotomous keys represented in the form of a table. Example - the following table shows a small dichotomous key that can be used to distinguish amongst 8 species of frogs and toads in central Ontario. This key can be used to determine the identification of the specimen shown in the image. Click through the interactive slides given below to understand how to use a dichotomous key like the one given here and to identify this specimen.
