Unit 1 Lesson 5 Classification of Living Things. Copyright Houghton Mifflin Harcourt Publishing Company

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2 Sorting Things Out! Why do we classify living things? Scientists classify living things based on characteristics that living things share. Classification helps scientists answer questions about organisms such as how many kinds there are, their characteristics, and their relationships.

3 How do scientists know living things are related? Physical characteristics, such as skeletal structure, can indicate whether organisms are similar or related. Scientists also study how organisms develop from an egg to an adult to determine if organisms are related.

4 How do scientists know living things are related? Chemical characteristics can indicate whether organisms are similar or related. Scientists study genetic material such as DNA and RNA, mutations, and genetic similarities to find relationships among organisms. Proteins and hormones can also show if organisms are related.

5 What s in a Name? How are living things named? Carolus Linnaeus simplified the naming of living things with a two-part scientific name. A species is a group of organisms that are very closely related. Members of the same species can mate and produce fertile offspring.

6 How are living things named? A genus includes similar species. A scientific name always includes the genus name followed by the specific name. The first letter is capitalized. The species name is lowercase. All organisms have a unique two-part scientific name that is italicized or underlined.

7 What are the levels of classification? Taxonomy is the science of describing, classifying, and naming living things. Scientists use an eight-level system to classify living things. Each level is more specific than the one above it, and it contains fewer kinds of living things.

8 What are the levels of classification? From most general to more specific, the levels of classification are domain, kingdom, phylum (plural, phyla), class, order, family, genus, and species.

9 Triple Play What are the three domains? Scientists once used a six-kingdom classification system, but later added the domain. A domain represents the largest differences among organisms in classification. The three domains are Bacteria, Archaea, and Eukarya.

10 What are the three domains? Domain Bacteria is made up of prokaryotes that usually have a cell wall and reproduce by cell division. All bacteria belong to this domain. Bacteria live in almost any environment: soil, water, and even inside the human body.

11 What are the three domains? Domain Archaea is made up of prokaryotes that differ from bacteria in their genetics and in the makeup of their cell walls. Archaea live in harsh environments, such as hot springs and thermal vents, where other organisms could not survive. Some archaea are found in the open ocean and in soil.

12 What are the three domains? Domain Eukarya is made up of all eukaryotes. Eukaryotes have cells with a nucleus and membrane-bound organelles. Some eukaryotes, such as protists and some fungi, are single-celled. Other protists as well as fungi, plants, and animals are multicellular.

13 My Kingdom for a Eukaryote! What are the four kingdoms in Eukarya? Scientists have classified four types of Eukarya. Scientists do this by deciding if an organism is unicellular or multicellular, and if it makes its own food, as well as how it reproduces.

14 What are the four kingdoms in Eukarya? Members of the kingdom Protista, called protists, are single-celled or simple multicellular organisms such as algae, protozoans, and slime molds. Protists are very diverse, with plant-like, animallike, or fungus-like characteristics. Some protists reproduce sexually, while others reproduce asexually. Some protists, autotrophs, make their own food. Other protists, heterotrophs, eat other organisms for food.

15 What are the four kingdoms in Eukarya? Members of the kingdom Fungi are single-celled or multicellular organisms such as yeasts, molds, and mushrooms. Fungi get energy by absorbing materials, and have cells with cell walls but no chloroplasts. Fungi use digestive juices to break down materials for food. They reproduce asexually or sexually, depending on their type.

16 What are the four kingdoms in Eukarya? Kingdom Plantae consists of multicellular organisms that have cell walls, mostly made of cellulose. Plants make food through photosynthesis. They are found on land and in water that light can pass through, and cannot move by themselves. Some plants reproduce sexually, when pollen from one plant fertilizes another. Some plants reproduce asexually, when buds grow into plants.

17 What are the four kingdoms in Eukarya? Kingdom Animalia contains multicellular organisms such as birds, fish, reptiles, insects, amphibians, and mammals that lack cell walls. Animals are typically able to move around and have specialized sense organs. They get nutrients by eating other organisms. Most animals reproduce sexually, but a few types of animals reproduce asexually, such as by budding.

18 How do classification systems change over time? Millions of organisms are not named. New organisms do not always fit into the existing classification system. Classification continues to change as scientists learn more about living things.

19 How do branching diagrams show classification relationships? Scientists often use a type of branching diagram called a cladogram, which shows relationships among species. Organisms are grouped according to common characteristics listed on a line. Branches of organisms extend from this line.

20 How do branching diagrams show classification relationships? Organisms on branches above a particular characteristic have the characteristic. Organisms on branches below the characteristic do not.

21 A Class by Themselves As scientists find more living things to study, they find that they may not have made enough classifications, or that their classifications may not describe organisms well enough. Some organisms are difficult to classify because they have traits that fall under more than one classification.

22 A Class by Themselves The sea spider is an arthropod because its body has segments and an exoskeleton. Sea spiders eat by sticking a straw-like structure into sponges and sea slugs and sucking out the juice. No other arthropod eats like this. To account for this strange mouth, scientists must decide if they need to create a new classification or change an existing one.

23 Keys to Success How can organisms be identified? A dichotomous key uses a series of paired statements to identify organisms. Each pair of statements is numbered. Either you choose the statement that best describes the organism, or you are directed to a new pair of statements. This process happens until you can identify the organism.