Table of Contents What Is Life? Classifying Organisms Domains and Kingdoms The Origin of Life

Life Comes From Life - What Is Life? Francesco Redi designed one of the first controlled experiments. In his experiment, Redi showed that flies do not spontaneously arise from decaying meat.

Life Comes From Life - What Is Life? Louis Pasteur’s carefully controlled experiment demonstrated that bacteria arise only from existing bacteria.

Using Prior Knowledge - What Is Life? Look at the section headings and visuals to see what this section is about. Then write what you already know about living things in a graphic organizer like the one below. As you read, write what you learn. What You Know Living things grow. Living things are made of cells. What You Learned Unicellular organisms are composed of only one cell. The cells of living things are composed of chemicals. The cells of organisms use energy to do things they must do.

End of Section: What Is Life?

Levels of Classification - Classifying Organisms Levels of Classification As you move down the levels of classification, the number of organisms decreases. The organisms at lower levels share more characteristics with each other.

Aristotle and Classification - Classifying Organisms Aristotle and Classification Many hundreds of years before Linnaeus, a Greek scholar named Aristotle developed a classification system for animals. Aristotle first divided animals into those he considered to have blood and those he did not. This graph shows Aristotle’s classification system for “animals with blood.”

Aristotle and Classification - Classifying Organisms Aristotle and Classification Reading Graphs: Into how many groups were these animals classified? 3

Aristotle and Classification - Classifying Organisms Aristotle and Classification Interpreting Data: Which group made up the largest percentage of animals? Animals that fly

Aristotle and Classification - Classifying Organisms Aristotle and Classification Calculating: What percentage of these animals either fly or swim? 78%

Aristotle and Classification - Classifying Organisms Aristotle and Classification Inferring: In Aristotle’s classification, where would a cow be classified? A whale? Cow- animals that walk, run, or crawl; whale- animals that swim.

Aristotle and Classification - Classifying Organisms Aristotle and Classification Predicting: Would Aristotle’s classification system be used today? Explain. Possible answer: This system includes only three categories, so it may not be very useful today. It also does not match that of modern scientists, who use characteristics other than movement to classify animals. For example, frogs and lions belong to very different groups.

Taxonomic Keys - Classifying Organisms Taxonomic keys are useful tools for determining the identity of organisms.

Evolution and Classification - Classifying Organisms Evolution and Classification Species with similar evolutionary histories are classified more closely together. These Galapagos finches may have arisen from a single species and changed gradually over time to become three separate species. Notice the differences in their appearance, especially their beaks. eats eats eats

Asking Questions - Classifying Organisms Before you read, preview the red headings. In a graphic organizer like the one below, ask a what, why, or how question for each heading. As you read, write the answers to your questions. Question Answer Why do scientists classify? Scientists classify because they want to organize living things into groups so they are easier to study. What system did Linnaeus use to name organisms? He used a system called binomial nomenclature. What are the levels of classification? Domain, kingdom, phylum, class, order, family, genus, species

More on Classifying Living Things - Classifying Organisms More on Classifying Living Things Click the PHSchool.com button for an activity about classifying living things.

End of Section: Classifying Organisms

Three Domains of Life - Domains and Kingdoms In the three-domain system of classifications, all known organisms belong to one of three domains–Bacteria, Archaea, or Eukarya.

Comparing and Contrasting - Domains and Kingdoms Comparing and Contrasting As you read, compare and contrast the characteristics of organisms in domains Bacteria, Archaea, and Eukarya by completing a table like the one below. Characteristics of Organisms Domain or Kingdom Cell Type and Number Able to Make Food? Bacteria Prokaryotes; unicellular Some are able to make food Archaea Prokaryotes; unicellular Some are able to make food Eukarya: Protists Eukaryotes; unicellular or multicellular Some are able to make food Fungi Eukaryotes; unicellular or multicellular No Plants Eukaryotes; multicellular Yes Animals Eukaryotes; multicellular No

Click the SciLinks button for links on kingdoms. - Domains and Kingdoms Links on Kingdoms Click the SciLinks button for links on kingdoms.

End of Section: Domains and Kingdoms

The Atmosphere of Early Earth - The Origin of Life The Atmosphere of Early Earth On ancient Earth, water vapor, carbon dioxide, and methane were probably the most abundant gases in the atmosphere. There were frequent volcanic eruptions, earthquakes, and violent storms.

Identifying Supporting Evidence - The Origin of Life Identifying Supporting Evidence As you read, identify the evidence that supports scientists’ hypothesis of how life arose on Earth. Write the evidence in a graphic organizer like the one below. Evidence Fossil evidence of achaea-like organisms Hypothesis Origin of life Fossils dated to be between 3.4 and 3.5 billion years old.

Links on the Origin of Life Click the SciLinks button for links on the origin of life.

End of Section: The Origin of Life

Graphic Organizer Living Things Food Homeostasis Water Living space need Food Homeostasis Water Living space made by to provide Autotrophs Shelter Food & water eaten by Heterotrophs

End of Section: Graphic Organizer