Life: From the First Organism Onward
Lesson 9.2: The Evolution of Multicellular Life
9.2. THE EVOLUTION OF MULTICELLULAR LIFE
Key Concept
Multicellular life evolved in the late Precambrian. The Precambrian ended with a mass extinction. It was followed by the Cambrian explosion, which began the Paleozoic Era. During the Paleozoic, major groups of organisms evolved, and plants, amphibians, and reptiles moved to the land. The Paleozoic ended with the Permian extinction. The following Mesozoic Era was the age of dinosaurs. The current Cenozoic Era is the age of mammals.
Standards
• CA.9–12.IE.1.d
• NSES.9–12.C.3.2, 4
• AAAS.9–12.5.A.1; AAAS.9–12.5.F.8, 9
Lesson Objectives
• Describe important events of the late Precambrian.
• Give an overview of evolution during the Paleozoic Era.
• Explain why the Mesozoic Era is called the age of the dinosaurs.
• Outline the main evolutionary events of the Cenozoic Era.
Lesson Vocabulary
• Cambrian explosion: spectacular burst of new life that occurred at the start of the Paleozoic Era
• Cenozoic Era: age of mammals that lasted from 65 million years ago to the present
• mass extinction: extinction event in which many if not most species abruptly disappear from Earth
• Mesozoic Era: age of dinosaurs that lasted from 245 million years ago to 65 million years ago
• Palezoic Era: age of “old life” from 544–245 million years ago that began with the Cambrian explosion and ended with the Permian extinction
• Permian extinction: extinction at the end of the Paleozoic Period that was the biggest mass extinction the world had ever seen until then
9.2. THE EVOLUTION OF MULTICELLULAR LIFE
Teaching Strategies
Introducing the Lesson
Most students will have prior knowledge of dinosaurs, so use dinosaurs as an example to introduce the evolution of multicellular life. Call on several students to state anything they know about dinosaurs. Make a list on the board.
Tell students they will read about the evolution of dinosaurs and other multicellular organisms in this lesson.
Demonstration
As you discuss the evolution of multicellular life, display online illustrations of important events and organisms that characterized the different geological periods since the beginning of the Cambrian. This will help make the information in the lesson come to life. The Web sites below are recommended for their excellent images of the history of life, including extant organisms.
• http://www.ucmp.berkeley.edu/alllife/eukaryota.html
• http://tolweb.org/tree/
• http://www.dlib.org/dlib/october05/10featured-collection.html
• http://www.uoregon.edu/ bsl/astronomy/
Differentiated Instruction
Prepare a gallery walk by posting the names of the geologic periods on large sheets of paper in different parts of the room. Divide the class into groups, being cognizant of the limitations of any special needs students. Ask groups of students to move from period to period and write on the posted papers any information they can recall about the periods. After the gallery walk, discuss the information they recorded. Point out any errors and underscore important points. SN
Enrichment
Ask a small group of students to create a diorama representing one of the geologic periods described in the lesson.
The diorama should illustrate the climate and the major types of organisms that lived during the period. Display their completed diorama in the classroom. Challenge other students to identify the period it represents.
Science Inquiry
Have groups of students do the activity Earth History: Time Flies, No Matter What the Scale (see URL below).
They will order important events in the history of life on a model of the geologic time scale. They will also relate the geologic time scale to an annual calendar. An answer key is included.
• http://www.asm.org/index.php?option=com_content#38;view=article#38;id=90592#38;Itemid=520
Overcoming Misconceptions
The idea that evolution is a conscious striving for perfection is a common misconception. Explain to the class that organisms do not try to evolve new traits; that evolution helps organisms adapt to changing environments, not become perfect; and that so-called “lower” organisms may be better adapted to their environments than so-called CHAPTER 9. TE LIFE: FROM THE FIRST ORGANISM ONWARD
“higher” organisms. Point out that some organisms, including cockroaches and sharks, have changed very little for millions of years because their ancient traits have allowed them to survive and reproduce despite environmental changes.
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Review Questions
Have students answer the Review Questions that are listed at the end of the lesson in their FlexBook.
• Sample answers to these questions will be provided upon request. Please send an email to [email protected] to request sample answers.
Points to Consider
The human species evolved during the Cenozoic Era. The scientific name of the human species is Homo sapiens.
• Do you know what this name means? Do you know why species are given scientific names?
– (Homo sapiens literally means “wise human.” Species are given scientific names so they have a unique, consistently used identifier.)
• What is a species? What determines whether a group of organisms is considered a species?
– (A species is a type of living thing, such as Homo sapiens. A group of organisms is considered a species if members of the group can mate and produce fertile offspring together but not with members of other such groups.)
9.2. THE EVOLUTION OF MULTICELLULAR LIFE
9.3 Classification
Key Concept
The Linnaean classification system is based on similarities in obvious physical traits. It consists of a hierarchy of taxa, from the species to the kingdom, and gives each species a unique genus and species name. The recently added domain is a larger and more inclusive taxon than the kingdom. Phylogeny is the evolutionary history of group of related organisms. It is represented by a phylogenetic tree. A clade is used to classify organisms based on evolutionary relationships.
• Outline the Linnaean classification, and define binomial nomenclature.
• Describe phylogenetic classification, and explain how it differs from Linnaean classification.
Lesson Vocabulary
• binomial nomenclature: method of naming species with two names, consisting of the genus name and species name
• clade: group of related organisms that includes an ancestor and all of its descendants
• domain: taxon in the revised Linnaean system that is larger and more inclusive than the kingdom
• genus: taxon above the species in the Linnaean classification system; group of closely related species
• kingdom: largest and most inclusive taxon in the original Linnaean classification system
• Linnaean classification system: system of classifying organisms based on observable physical traits; consists of a hierarchy of taxa, from the kingdom to the species
• phylogenetic tree: diagram that shows how species are related to each other through common ancestors
• phylogeny: evolutionary history of a group of related organisms
• species: group of organisms that are similar enough to mate together and produce fertile offspring
• taxa: (singular, taxon) grouping of organisms in a classification system, such as the Linnaean system; for example, species or genus
• taxonomy: science of classifying organisms
CHAPTER 9. TE LIFE: FROM THE FIRST ORGANISM ONWARD
Teaching Strategies
Introducing the Lesson
On the board, write the scientific name of a common species such as the domestic cat (Felis catus). Call on volunteers to explain (or explain yourself if necessary) what the two parts of the name represent (the genus and species names).
Tell the class they will learn more about how organisms are named and classified in this lesson.
Activity
Students can apply principles of Linnaean and phylogenetic classification by doing the activities at the URLs below. In the first activity, they will develop a classification system for different kinds of “organisms” in the “pasta kingdom.” In the second activity, they will apply cladistics to a group of organisms represented by a collection of nails, screws, and bolts.
• http://www.accessexcellence.org/AE/ATG/data/released/0070-JudithAllard/
• http://www.pbs.org/wgbh/nova/teachers/activities/2905_link.html
Differentiated Instruction
Help students focus on the main ideas in the lesson. Pair less proficient readers with more proficient readers, and ask partners to complete cloze sentences, such as those below, while they read the lesson. LPR
a. Taxonomy is ... (a method of organizing living things into groups.)
b. Biologists classify organisms in order to ... (make sense of the incredible diversity of life on Earth.) c. Binomial nomenclature is ... (Linnaeus’ method of naming species.)
d. The scientific name of a species consists of ... (its genus and species names.)
Enrichment
Ask a small group of students who need extra challenges to create a taxonomy board game. The object of the game should be to identify correctly an organism’s species based on a series of increasingly specific clues about the organism’s traits. Encourage other students to play the game.
Science Inquiry
Have groups of students create a cladogram for the “evolution” of a familiar technology, such as audio devices. Stu-dents can do online research to identify the sequence in which major innovations occurred in their technology. (For example, audio devices evolved through stages of record players, 8-track tape players, cassette players, Walkmans, CD players, and iPods). Discuss their completed cladograms, and relate them to cladograms in the evolution of life.
Overcoming Misconceptions
Students may have the misconception that evolutionary relationships are linear, when in fact phylogenies are branched like bushes. At the URL below, you can find an interactive cartoon series that cleverly makes this point and clarifies the misconception.
• http://www.indiana.edu/ ensiweb/famtree_v_phylog.html 9.3. CLASSIFICATION
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in the CK-12 Biology Workbook. Ask students to complete the worksheets alone or in pairs as a review of lesson content.
Review Questions
Have students answer the Review Questions that are listed at the end of the lesson in their FlexBook.
• Sample answers to these questions will be provided upon request. Please send an email to [email protected] to request sample answers.
Points to Consider
This chapter gives you a glimpse of 4 billion years of evolution on Earth. In the next chapter, you will read about the forces that bring about evolution. Natural selection is one of these forces. It generally results in a population or species becoming better adapted to its environment over time.
• How does natural selection work? How does it bring about evolutionary change?
– (Fitter members of a species live longer and produce more offspring than other members of the species.
Over time, their traits become more common in the species.)
• What might be the other forces of evolution?
– (Students might mention mutation, but they may not be able to identify gene flow or genetic drift.)
CHAPTER 9. TE LIFE: FROM THE FIRST ORGANISM ONWARD
9.4 Worksheet Answer Keys
• The worksheet answer keys are available upon request. Please send an email to [email protected] to request the worksheet answer keys.
9.4. WORKSHEET ANSWER KEYS