[Music] hi and welcome back to three sighs lessons cold UK by the end of this video you should be able to describe how organisms are classified based on their characteristics you should then be able to describe the three domain classification system and finally you should be able to use an evolutionary tree to describe the relationships between organisms in previous videos we've seen the enormous variety of living organisms on planet Earth there were literally millions of different species as more and more species were discovered scientists realized that they often have characteristics in common I'm showing a good example here all of these animals are different species but they all have similar characteristics now in the 1700s the scientist Colin næss began to classify species into different categories based on the structure and characteristics in the exam you could be us to use the classification system that Linnaeus developed I should point out that this looks more complicated than it actually is the first key idea that you need to understand is that Linnaeus divided all living organisms into two kingdoms these are the animal kingdom on the plant kingdom Linnaeus then divided each kingdom into a number of smaller categories I'm showing you all the categories here so we have kingdom phylum class order family genus and species now you need to learn this system and one way is to use this mnemonic King Phillip came over for good soup now in the exam you could be shown the classification of an organism so I'm showing you that here four species of zebra in the exam question they might miss our part of the classification and ask you to fill it in so in this case the missing pod is class and I'm showing you that here now every organism is named from their gymnast and their species so for example this zebra has the name equus quagga scientists call this the binomial system and the word binomial means two names so again in the exam you could be shown the classification of an organism and ask to state the binomial name I'm showing you here the classification for polar bears I'd like to state the binomial name for the polar bear so pause the video now and try this yourself okay remember that the binomial name is the Janice and the species so in this case the binomial name for the polar bear is Ursus maritimus now the key fact about this classification system is that it's based on characteristics that we can see for example the shape of the body or the number of toes however there be major advances in biology since this system was developed for example we can now use microscopes to look at internal structures we can also analyze an organisms biochemistry for example its DNA and look for similarity to other species now scientists use the three domain system this was developed by the scientist call worse who compared the biochemistry of different organisms in the three domain system we've got our key which are primitive bacteria archaea are often found in extreme conditions such as hot springs we then have true bacteria such as the kind that live in the human digestive system and finally we've got eukaryota these include animals plants and fungi eukaryota also includes protists such as amoeba now scientists use evolutionary trees to show how closely related organisms are to each other to make an evolutionary tree scientists can use classification data on living organisms for example their DNA however for extinct organisms scientists have to use fossils and this can present a problem as the fossil records of many species are incomplete I'm showing you an evolutionary tree here species one and two are closely related to each other whereas species 3 is more distantly related however species one two and three all share a common ancestor we wanna find plenty of questions on classification and evolutionary trees in my revision workbook and you can get that by clicking on the link above [Music]