Classification of life

1. (27.5) Classification of life

2. How do we tell living things apart?

3. Definition: the study of grouping living things based on their shared characteristics. Each organism is placed into larger and larger categories called taxa (plural form of taxon). Carl Linnaeus was a HUGE contributor to this. Systematics

4. All my work… summed up in a cheap MS Paint picture. Thou art cruel, Mr. Paschak

5. In modern biology, we use the following taxa/categories (from LEAST specific to MOST specific): • Domain • Kingdom • Phylum • Class • Order • Family • Genus • Species Systematics There are only 3 domains, but around 2 million species (discovered so far). Some estimates place the number of species on Earth at 8.7 million. **As you go lower down the ranking, the number of taxa increases.**

6. Definition: the assignment of a specific scientific name to an organism. • An organism’s name is usually binomial (contains two words) – its Genus and its species are listed. Linnaeus created this approach. • Eg: Homo sapiens, Escherichia coli • These can be abbreviated • Eg: H. sapiens, E. coli Taxonomy

7. Definition: the evolutionary relationship among organisms. • The goal of systematics is to put closely-related species into similar groups. • Classification should reflect phylogeny. • Members of the same family should be more related than members of a different family. Phylogeny

8. Living things are divided into five kingdoms based on: • Whether or not their cells have nuclei. • How many cells they’re made up of. • How they obtain their food/nutrition. The five-kingdom system

9. The five kingdom system

10. Suggests that monerans (bacteria, archaea) evolved first and don’t have nuclei. Protists evolved from monerans. Plants, animals, and fungi share some common, protist ancestor. This system is now considered to be inaccurate, though. The five kingdom system

11. Carl Woese’s analysis of bacteria suggested that they should be divided into two kingdoms: • Eubacteria (also called “true” bacteria) and • Archaebacteria • This caused the creationof a sixth kingdom. The six kingdom system

12. Evidence in DNA and RNA (ribonucleic acid) helps to sort living things into larger domains. Domains are based on RNA, molecular evidence, and cell structures. The three domains are: Eukarya, Bacteria, and Archaea. Three-Domain System

13. Three-domain system

14. All bacteria are prokaryotes (they have no nuclei) and unicellular (a whole bacterium is made up of just one cell). Found in nearly every environment you can think of. bacteria

15. Also unicellular prokaryotes. • Have a different cell wall and membrane compared to bacteria. • Tend to inhabit extreme conditions • Highly salty waters • Hot springs • Extremely cold waters • More closely-related to Eukarya than to bacteria. Archaea

16. All of these organisms are eukaryotes (have cells that contain a nucleus). Can be either unicellular (protists, yeasts) or multicellular (plants, animals, many fungi). This domain is made up of 4 of the original five kingdoms (Plantae, Animalia, Fungi, and Protista). Eukarya

17. How to figure out which category is the right one… Categorical logic

18. If something is true about a category, then it MUST be true for ALL members of that category. This is called categorical reasoning. It is the basis for classification. It looks like this: Premise: All wizards wear glasses. Given: Mr. Paschak wears glasses. Conclusion: Mr. Paschak is a wizard. Logic in classification

19. Example: Premise: All birds are vertebrates. Given: A robin is a bird. Conclusion: A robin is a vertebrate. Using this example, construct an argument to show that Mr. Paschak is a mammal. Logic in classification

20. Construct a categorical argument to show that a spruce tree is a plant. Consider this argument: Premise: All horses are herbivores. Given: Organism X is a herbivore. Conclusion: Organism X is a horse. Is this argument correct? Why or why not? Quick assignment

21. Consult section 1.2 of your textbook and/or an online resource in order to find the following: • Two defining characteristics of Archaea • Two defining characteristics of Bacteria (or Eubacteria) • Two defining characteristics of Eukarya. • Arrange these into a table in your notes. For next time

22. Also called “phylogenetics”. This is the new direction in classification. Organisms are put into groups called clades. Each clade contains an ancestor and ALL species that have descended from it. Continued… (incoming t-chart!) Cladistics

23. Phylogenetics Traditional view • Organisms arranged by ancestry (shared genes, common ancestors). • Grouped into different clades. • Physical characteristics within a clade can be VERY different. • Organisms arranged by physical characteristics. • Grouped into phyla, classes, orders, etc. • Physical characteristics in groups tend to be similar. PhylogeneticsVs taxonomy

24. Note that in this diagram, 7 distinct animals all belong to a single clade! Cladograms

25. CAREFUL! Even though the cladogram used one trait at a time to arrange the organisms, real phylogeneticists will use much more data. • Data for creating clades includes: • Physical characteritics • DNA sequences and genes • RNA sequences Cladograms