Chapter 14 Redi’s Experiment Section 1 Biogenesis Chapter 14 Redi’s Experiment Before the 1600s, it was generally thought that organisms could arise from nonliving material by spontaneous generation.

Redi’s Experiment, continued Section 1 Biogenesis Chapter 14 Redi’s Experiment, continued Redi showed in 1668 that rotting meat kept away from flies would not produce new flies. Maggots appeared only on meat that had been exposed to flies.

Spallanzani’s Experiment Section 1 Biogenesis Chapter 14 Spallanzani’s Experiment Spallanzani showed in the 1700s that microorganisms would not grow in broth when its container was heated and then sealed. He inferred that microorganisms do not arise spontaneously but, rather, are carried in the air.

Spallanzani’s Experiment Section 1 Biogenesis Chapter 14 Spallanzani’s Experiment

Chapter 14 Pasteur’s Experiment Section 1 Biogenesis Chapter 14 Pasteur’s Experiment Pasteur in the 1800s used a variation of Spallanzani’s design to prove that microorganisms are carried in the air and do not arise by spontaneous generation.

Section 1 Biogenesis Chapter 14 Pasteur’s Experiment

Miller-Urey Experiment Section 2 Earth’s History Chapter 14 Miller-Urey Experiment

From Molecules to Cell-Like Structures Section 2 Earth’s History Chapter 14 From Molecules to Cell-Like Structures Cell-like structures, including microspheres and coacervates, form spontaneously in certain kinds of solutions. These structures could have been a step in the formation of modern cells but lack hereditary material.

Chapter 14 The First Cells Section 3 The First Life-Forms Chapter 14 The First Cells The first cells that formed on Earth were probably heterotrophic prokaryotes.

The First Cells, continued Section 3 The First Life-Forms Chapter 14 The First Cells, continued Chemosynthesis The first autotrophic cells probably used chemosynthesis to make food. Chemosynthesis produces energy through the oxidation of inorganic substances, such as sulfur.

The First Cells, continued Section 3 The First Life-Forms Chapter 14 The First Cells, continued Photosynthesis and Aerobic Respiration Most modern autotrophic cells, such as cyanobacteria, use photosynthesis to make food. An important byproduct of photosynthesis is oxygen.

The First Cells, continued Section 3 The First Life-Forms Chapter 14 The First Cells, continued Photosynthesis and Aerobic Respiration Once oxygen began to accumulate on Earth, cells would need to bind oxygen to other compounds in order to prevent damage to cell enzymes. This binding function may have been a first step toward aerobic respiration in cells.

Chapter 14 The First Eukaryotes Section 3 The First Life-Forms Chapter 14 The First Eukaryotes Eukaryotic cells may have evolved from large prokaryotic cells that engulfed smaller prokaryotic cells. This is known as the theory of endosymbiosis. The engulfed prokaryotic cells may have become the ancestors of organelles such as mitochondria and chloroplasts.

Conditions on early Earth made the origin of life possible Earth formed 4.6 billion years ago The first living things were very simple and heterotrophic. They arose about 4 billion years ago First photosynthetic organisms were apparent about 3.5 billion years ago Clarify to students that the first living things must have been very simple. Cyanobacteria are far too complex to be the first cells. Students might not appreciate the challenges of finding fossils of early life. These early life forms were likely microscopic and free of hard parts such as shells and bone. Over time, geological heat, pressure, and friction may destroy fossils. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not created from scratch. Unlike baking a cake or constructing an automobile, where components are assembled to create something new, the reproduction of cells does not currently involve anything other than cells. 2. Some students might think that scientists have answers for all of life’s questions. Other students might rely upon supernatural explanations when faced with scientific uncertainty. The material in this chapter provides a good opportunity to further distinguish between the process of science and other ways of knowing. 3. Most of us are unable to comprehend the vast lengths of time considered by geologists. Exercises and examples can increase this comprehension. Consider the number of seconds in a year (60  60  24  365.25  31,557,600) or how much money you could spend each day if you spent $1 million dollars a year ($1,000,000/365  $2,739.73/day). 4. Students may need to be reminded that one billion is 1,000 million. Many students (and some politicians) easily confuse million and billion without realizing the scale of the error. Challenge students to translate either of the examples above to illustrate one billion. (For example, one billion seconds equals about 31.7 years. If you were to spend one billion dollars in a year, you would need to spend $2,739,730 each day of that year!) Teaching Tips 1. Students who have studied cell theory might wonder how the first cells formed. Furthermore, they might wonder if spontaneous generation of cells could occur today. Module 15.1 describes how conditions on the surface of Earth when life first formed were dramatically different from today. Furthermore, if new life were evolving on Earth today, it would face competition from the vast amount of life already present. 2. Consider pointing out the logic of the theory of spontaneous generation, given the state of scientific knowledge during that period in history. Piles of manure and rotting flesh left in the open would apparently produce flies out of nowhere. At that time, so little was understood about eggs, sperm, and fertilization that spontaneous generation was a logical conclusion. 3. The four-stage hypothesis for the origin of life is a little like a recipe for building cells from the bottom up. If your students do not remember details about biological molecules and basic cell structure, you may need to review them before addressing these stages. 4. At some point in the presentation of the four-stage hypothesis for the origin of life, students should be encouraged to consider at what point “life” exists. Are self-replicating, RNA-based, membrane-bound structures alive? Discussing the evolution of the first cells helps clarify definitions of life. Copyright © 2009 Pearson Education, Inc.

The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Prokaryotes lived alone on Earth for 1.5 billion years They created our atmosphere and transformed Earth’s biosphere Virtually all metabolic pathways evolved within prokaryotes Atmospheric oxygen appeared 2.7 billion years ago due to prokaryotic photosynthesis Cellular respiration arose in prokaryotes, using oxygen to harvest energy from organic molecules Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Multicellular forms arose about 1.5 billion years ago The descendents of these forms include a variety of algae, plants, fungi, animals The oldest known fossils of multicellular organisms were small algae, living 1.2 billion years ago Comprehending the length of time of the major phases of life’s history is problematic for most students. Point out to your students that multicellular life represents only about 13% of Earth’s history (0.6 of 4.6 billion years). The period in which all life on Earth was prokaryotic lasted more than twice the period of time since multicellular life evolved. Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.

The origins of single-celled and multicelled organisms and the colonization of land are key events in life’s history Arthropods and tetrapods are the most widespread and diverse land animals Human lineage diverged from apes 6-7 million years ago Our species originated 160,000 years ago Student Misconceptions and Concerns 1. Figure 15.4 presents an analogy between a clock face and the history of Earth. Students might wonder if all of Earth’s history represents just one cycle of the clock face, lasting by analogy 12 hours, or two cycles of the clock face, lasting 24 hours. You might note that this is a 24-hour clock face. The module ends by noting that the clock face might represent just a single hour. 2. Comprehending the length of time of the major phases of life’s history is problematic for most students. Even the mass extinction of most dinosaurs 65 million years ago took place far beyond any period in recorded human history (65 million years ago is about 27,000 times the period of time since the life of Aristotle). Consider noting, as a reference point, that multicellular life, as we know it today, has existed for only about 13% of Earth’s history (0.6 of 4.6 billion years). The period during which only prokaryotic life existed on earth was more than twice as long as the amount of time multicellular life has existed. Other proportional comparisons can help to put these periods in perspective. Teaching Tips 1. The evolution from prokaryotes to eukaryotes and single-celled life to multicellular life represent major leaps and dramatic change. Consider pointing out to students that extensive amounts of time did pass between each of these dramatic transitions. 2. Assigning students, individually or in small groups, to create timelines using the dates in Table 15.6 can help them appreciate the proportional relationship of these periods. Copyright © 2009 Pearson Education, Inc.