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

2. 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.

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

4. 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.

5. End of Section: What Is Life?

6. 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.

7. 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.”

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

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

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

11. 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.

12. 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.

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

14. 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

15. 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

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

17. End of Section: Classifying Organisms

18. 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.

19. 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

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

21. End of Section: Domains and Kingdoms

22. 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.

23. 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.

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

25. End of Section: The Origin of Life

26. 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

27. End of Section: Graphic Organizer