Chapter 7

Chapter 7Classifying Living Things

Classify:•To group ideas, information, or objects based on similarities.

Early History:Aristotle: Greek philosopher who developed the system of classification over 2000 years ago. The science of classifying and naming organisms is called taxonomy. He started to classify living things by starting with 2 kingdoms. A kingdom is the largest of the taxonomic categories. The two kingdoms that he started with were the plant and the animal kingdoms.

After he named the animal kingdom, he divided it even more by where they lived. Animals that lived on land and animals that lived in the water were in two different groups. The plant kingdoms were separated by size and structure. Even though Aristotle made a breakthrough by classifying living things, there were many other scientists that criticized him.

What was their reason?

There were too many exceptions to his rules.Frogs: live on land and water.Trees: are not related just because they are trees!!

Scientific NamingLinnaeus: a Swedish naturalist that created a new way to classify living things. The way that he classified these living things were by similarities in body structure and systems, size, shape, color, and methods of getting food. In his system, each organism has two names. This naming system is called binomial nomenclature.

The two names that each organism is given is called its scientific name or its Latin name. The first word is in the name is the Genus: a group of different organisms that have similar characteristics. The second word of its name is its specific name or species.

The whole name gives the name of a certain species: smallest most precise classification category.As you know, organisms of the same species can…reproduce with each other.Examples:Canis familiaris: dogCyanocitta cristata: Blue jayCanis latrons: CoyoteFelis catus: domestic catCanis lupus: WolfFelis onca: jaguar

Modern ClassificationAristotle and Linnaeus used characteristics of organisms that we easily observed. Today, scientists look at other traits to classify organisms. They look at chemical makeup of the organism and the organism’s ancestors. They look at similarities in genes and body structures. They also look at fossils and the embryos of an organism as it develops. By looking at these things, scientists can find the phylogeny of an organism.

Phylogeny: an organisms evolutionary histroy.

Classification is based on phylogeny!!

There are six Kingdoms in modern day classification!!

Animal• Eukaryotes• Many-celled• Move• Members eat plants and/or other

animals

Plants• Eukaryotes• Many-celled• Don’t move• Make their own food

Fungi• Eukaryotes• One and many-celled• Don’t move• Get it from other organisms

Protista• Eukaryotic• One and many-celled• Some move• Some make their own food and

some get it from other organisms

Eubacteria• Prokaryotic• One-celled• Some move• Some make their own food and

some get it from other organisms• Examples: streptococcus

Archebacteria• Prokaryotic• One-celled• Some move• Some make their own food and

some get it from other organisms

Organisms, as you can see, are placed in the kingdoms based on several characteristics. Some of these characteristics are presence or absence of a nucleus, single celled or multi-celled, ability to make food, and ability to move.

Prokaryote: organisms without a nucleus

Eukaryote: organisms with a nucleus

Kingdoms are also separated into smaller groups. These smaller groups are PhylumClassOrderFamilyGenusSpeciesEach is a division of the division before it.

Identifying OrganismsCommon names and scientific names:Just because an animal or plant have the same common name does not mean that they have the same scientific name. Also, an organism may have many different common names but their scientific name is the same.

Examples

• There are many kinds of birds that are called robins around the world…but they all have different scientific names.

• Mountain Lion, Cougar, Puma, Florida Panther: all are the same species!!

Scientific names serve 4 main purposes:1: Help scientists avoid errors in communication.  2: Organisms with similar evolutionary history are classified together.

3: Gives descriptive information about the species.   4: Allow information about organisms to be organized and found easily and efficiently.

Scientists classify living things by using more detailed lists of traits called a dichotomous key.Dichotomous keys are arranged in steps with two descriptive statements at each step. The steps are usually labeled 1a, 1b, 2a, 2b, and so on. To use the key that is given to you, you must always begin with a choice from the first pair of descriptions. At the end of each step you will either see a scientific name or directions to go to another step with more descriptions. You will eventually get to the species name of the animal or plant that you are looking for.