Lesson 4

STARTER: Identify the following

OBJECTIVES  To discuss the difference in approached between earlier and more recent classification systems  To explain the relationship between classification and phylogeny  To compare the five-kingdom and the three domain system

Aristotle, 4000 BC  Created 1 st written classification scheme based on Appearance Anatomy  2 Kingdom system: Plants Animals ○ Live and move in water ○ Live and move on land ○ Move through air

Problems with old system  Both kingdoms included single-celled organisms  Single-celled organisms that had both plant and animal features E.g. Euglena (can photosynthesise & has undilipodium)Euglena  Fungi Like plants: had root-like hyphae Like animals : do not photosynthesise but digest organic matter and absorb nutrients

Current classification system is based on  Physiology How living things work (e.g. How muscles contract, etc.)  Biochemistry  Genetics  Embryology  Evolution  Behaviour

Using biochemistry in classification  Comparing large biochemical molecules Differences in amino acid sequences reflect evolutionary distance  E.g cytochrome C Used in respiration Found in all organisms except chemosynthetic prokaryotes (those able to obtain energy from inorganic molecules or methane instead of sunlight )

Relationships between species based on sequences of cytochrome c

Genetics  Most accurate way to show relationships  The more similar the DNA or RNA sequences, the more closely related

Examining molecular connections In groups of 3, complete the sheet on molecular connections

The table shows the percentage difference between the coding DNA of humans, chimpanzees, gorillas and orangutans 1. Which two animals appear to be most closely related? 2. Which two are most distantly related? 3. Explain why these data cannot provide us with firm guidelines about whether humans and chimpanzees should be placed in the same genus. % difference in DNA Humans and chimpanzees 0.87 Humans and gorillas 1.04 Humans and orangutans 2.18 Chimpanzees and gorillas 0.99 Chimpanzees and orangutans 2.14 Gorillas and orangutans 2.25

Phylogeny  Tree of life  Phylogeny is used as a basis for classification

The more recent the common ancestor, the more closely related species are

The three domain system  By Carl Woese (1990) Based on RNA  Prokaryotae divided into: Bacteria (Eubacteria) and Archaea (Archaebacteria) BacteriaArchaea and Eukaryotae Different cell membrane structure Different flagella Different RNA polymerase (makes RNA) No histones Different mechanisms for making DNA and RNA Also differs Same RNA polymerase Have proteins bound to DNA Same mechanisms for making DNA and RNA

Question Discuss whether the five-kingdom and the three-kingdom classifications are completely different from one another, or if they could possibly be used together.

Answer  The three domains are the highest taxa.   It is possible to have the domain Eukarya, with the kingdoms Protoctista, Fungi, Plantae and Animalia as subdivisions of it.  However, we cannot keep the kingdom Prokaryota, as that is now split at a higher level. What do you notice about the position of the common ancestors of Archaea and Eukarya vs that of Bacteria and Archaea? What does this mean?

HOMEWORK  Practice Qs on Classification (in the resources folder in the VLE  On-line quiz on the VLE  The test on classification will be combined with the test at the end of Maintaining Diversity