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Explore the concept of life through experiments, classification systems, and evolutionary history. Learn about the characteristics of living things, levels of classification, and the three domains of life.
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Table of Contents • What Is Life? • Classifying Organisms • Domains and Kingdoms • The Origin of Life
- What Is Life? Life Comes From Life • Francesco Redi designed one of the first controlled experiments. In his experiment, Redi showed that flies do not spontaneously arise from decaying meat.
- What Is Life? Life Comes From Life • Louis Pasteur’s carefully controlled experiment demonstrated that bacteria arise only from existing bacteria.
- What Is Life? Redi’s and Pasteur’s Experiments • Click the Active Art button to open a browser windowand access Active Art about Redi’s and Pasteur’sexperiments.
- What Is Life? Using Prior Knowledge • 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.
- What Is Life? The Characteristics of Living Things • Click the Video button to watch a movie about the characteristics of living things.
- 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.
- 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.”
3 Reading Graphs: Into how many groups were these animals classified? - Classifying Organisms Aristotle and Classification
Animals that fly Interpreting Data: Which group made up the largest percentage of animals? - Classifying Organisms Aristotle and Classification
78% Calculating: What percentage of these animals either fly or swim? - Classifying Organisms Aristotle and Classification
Cow- animals that walk, run, or crawl; whale- animals that swim. Inferring: In Aristotle’s classification, where would a cow be classified? A whale? - Classifying Organisms Aristotle and Classification
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. Predicting: Would Aristotle’s classification system be used today? Explain. - Classifying Organisms Aristotle and Classification
- Classifying Organisms Taxonomic Keys • Taxonomic keys are useful tools for determining the identity of organisms.
- 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
Question Answer - Classifying Organisms Asking Questions • 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. 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
- Classifying Organisms More on Classifying Living Things • Click the PHSchool.com button for an activity about classifying living things.
- Domains and Kingdoms Three Domains of Life • In the three-domain system of classifications, all known organisms belong to one of three domains–Bacteria, Archaea, or Eukarya.
- 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
- Domains and Kingdoms Links on Kingdoms • Click the SciLinks button for links on kingdoms.
- 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.
- 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.
- The Origin of Life Links on the Origin of Life • Click the SciLinks button for links on the origin of life.
- The Origin of Life Modeling Conditions on Early Earth • Click the Video button to watch a movie about modeling conditions on early Earth.
Graphic Organizer Living Things need Homeostasis Food Living space Water made by to provide Autotrophs Shelter Food & water eaten by Heterotrophs
