The Evolution of Microbial Life

The Evolution of Microbial Life
Chapter 15 The Evolution of Microbial Life

Biology and Society: Can Life Be Created in the Lab?
How did life first arise on Earth? To gain insight, scientists have Synthesized the entire genome of Mycoplasma genitalium, a species of bacteria found naturally in the human urinary tract Transplanted the complete genome of one species of Mycoplasma bacteria into another © 2010 Pearson Education, Inc.

Figure Primitive life Figure 15.00

An artificial organism that could be completely controlled might
A research group led by Craig Venter hopes to Create an artificial genome Transplant it into a genome-free host cell An artificial organism that could be completely controlled might Clean up toxic wastes Generate biofuels Be unable to survive outside rigidly controlled conditions

MAJOR EPISODES IN THE HISTORY OF LIFE
Earth was formed about 4.6 billion years ago. Prokaryotes Evolved by 3.5 billion years ago Began oxygen production about 2.7 billion years ago Lived alone for almost 2 billion years Continue in great abundance today Student Misconceptions and Concerns 1. Students often have difficulty grasping the enormity of time. Perhaps surprisingly, many students do not understand that a billion is a thousand times greater than a million. Exercises and examples that help students comprehend such large numbers should be considered, so that students can understand these tremendous periods for evolutionary diversification. Here are just a few examples to consider: a. If an earthquake or volcano erupts just once, every thousand years or so, how often will this event occur in a million years? (One thousand times.) Note that what is rare to us becomes “common” in geological terms. b. Have students calculate the age of a human when they reach their 1 billionth second of life. (Starting with birth, the answer is years.) 1,000,000,000 (seconds) = (years) x (days in a year) x 24 (hours in a day) x 60 (minutes) x 60 (seconds). Then have them calculate how long it takes to live 1,000,000 seconds. (About days.) Teaching Tips 1. Consider making some sort of timeline to scale in a hallway, long laboratory, or the side of the lecture hall. Mark these proportional periods: The full length of time is 4.6 billion years. The percentages below were calculated using the textbook’s approximate dates for each of these events. 0.0%—The Earth forms. 13%—The Earth’s crust solidifies. 24%—The first life appears. 41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere. 54%—The first eukaryotes appear. 74%—The first multicellular eukaryotes appear. 89%—Plants first invade land. 99.9%—Human and ape ancestries diverge! 2. Students might need to be reminded about the reactive properties of oxygen. Note that rust is the result of oxygen interacting with iron. Oxygen is highly reactive and could interfere with life-forming chemical processes today.

Single-celled eukaryotes first evolved about 2.1 billion years ago.
Multicellular eukaryotes first evolved at least 1.2 billion years ago. Student Misconceptions and Concerns 1. Students often have difficulty grasping the enormity of time. Perhaps surprisingly, many students do not understand that a billion is a thousand times greater than a million. Exercises and examples that help students comprehend such large numbers should be considered, so that students can understand these tremendous periods for evolutionary diversification. Here are just a few examples to consider: a. If an earthquake or volcano erupts just once, every thousand years or so, how often will this event occur in a million years? (One thousand times.) Note that what is rare to us becomes “common” in geological terms. b. Have students calculate the age of a human when they reach their 1 billionth second of life. (Starting with birth, the answer is years.) 1,000,000,000 (seconds) = (years) x (days in a year) x 24 (hours in a day) x 60 (minutes) x 60 (seconds). Then have them calculate how long it takes to live 1,000,000 seconds. (About days.) Teaching Tips 1. Consider making some sort of timeline to scale in a hallway, long laboratory, or the side of the lecture hall. Mark these proportional periods: The full length of time is 4.6 billion years. The percentages below were calculated using the textbook’s approximate dates for each of these events. 0.0%—The Earth forms. 13%—The Earth’s crust solidifies. 24%—The first life appears. 41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere. 54%—The first eukaryotes appear. 74%—The first multicellular eukaryotes appear. 89%—Plants first invade land. 99.9%—Human and ape ancestries diverge! 2. Students might need to be reminded about the reactive properties of oxygen. Note that rust is the result of oxygen interacting with iron. Oxygen is highly reactive and could interfere with life-forming chemical processes today.

Common ancestor to all present-day life
Precambrian Common ancestor to all present-day life Atmospheric oxygen begins to appear due to photosynthetic prokaryotes Figure 15.1a Some major episodes in the history of life. Origin of Earth Earth cool enough for crust to solidify Oldest prokaryotic fossils 4,500 4,000 3,500 3,000 2,500 Millions of years ago Figure 15.1a

Figure 15.1b Figure 15.1b Some major episodes in the history of life.
Paleozoic Mesozoic Cenozoic Bacteria Prokaryotes Archaea Protists Eukaryotes Plants Fungi Animals Figure 15.1b Some major episodes in the history of life. Cambrian explosion Oldest eukaryotic fossils Origin of multicellular organisms Oldest animal fossils Plants and symbiotic fungi colonize land Extinction of dinosaurs First humans 2,000 1,500 1,000 500 Millions of years ago Figure 15.1b

All the major phyla of animals evolved by the end of the Cambrian explosion, which began about 540 million years ago and lasted about 10 million years. Plants and fungi First colonized land about 500 million years Were followed by amphibians that evolved from fish Student Misconceptions and Concerns 1. Students often have difficulty grasping the enormity of time. Perhaps surprisingly, many students do not understand that a billion is a thousand times greater than a million. Exercises and examples that help students comprehend such large numbers should be considered, so that students can understand these tremendous periods for evolutionary diversification. Here are just a few examples to consider: a. If an earthquake or volcano erupts just once, every thousand years or so, how often will this event occur in a million years? (One thousand times.) Note that what is rare to us becomes “common” in geological terms. b. Have students calculate the age of a human when they reach their 1 billionth second of life. (Starting with birth, the answer is years.) 1,000,000,000 (seconds) = (years) x (days in a year) x 24 (hours in a day) x 60 (minutes) x 60 (seconds). Then have them calculate how long it takes to live 1,000,000 seconds. (About days.) Teaching Tips 1. Consider making some sort of timeline to scale in a hallway, long laboratory, or the side of the lecture hall. Mark these proportional periods: The full length of time is 4.6 billion years. The percentages below were calculated using the textbook’s approximate dates for each of these events. 0.0%—The Earth forms. 13%—The Earth’s crust solidifies. 24%—The first life appears. 41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere. 54%—The first eukaryotes appear. 74%—The first multicellular eukaryotes appear. 89%—Plants first invade land. 99.9%—Human and ape ancestries diverge! 2. Students might need to be reminded about the reactive properties of oxygen. Note that rust is the result of oxygen interacting with iron. Oxygen is highly reactive and could interfere with life-forming chemical processes today.

What if we use a clock analogy to tick down all of the major events in the history of life on Earth?
Student Misconceptions and Concerns 1. Students often have difficulty grasping the enormity of time. Perhaps surprisingly, many students do not understand that a billion is a thousand times greater than a million. Exercises and examples that help students comprehend such large numbers should be considered, so that students can understand these tremendous periods for evolutionary diversification. Here are just a few examples to consider: a. If an earthquake or volcano erupts just once, every thousand years or so, how often will this event occur in a million years? (One thousand times.) Note that what is rare to us becomes “common” in geological terms. b. Have students calculate the age of a human when they reach their 1 billionth second of life. (Starting with birth, the answer is years.) 1,000,000,000 (seconds) = (years) x (days in a year) x 24 (hours in a day) x 60 (minutes) x 60 (seconds). Then have them calculate how long it takes to live 1,000,000 seconds. (About days.) Teaching Tips 1. Consider making some sort of timeline to scale in a hallway, long laboratory, or the side of the lecture hall. Mark these proportional periods: The full length of time is 4.6 billion years. The percentages below were calculated using the textbook’s approximate dates for each of these events. 0.0%—The Earth forms. 13%—The Earth’s crust solidifies. 24%—The first life appears. 41%—Photosynthetic prokaryotes start producing an oxygen-rich atmosphere. 54%—The first eukaryotes appear. 74%—The first multicellular eukaryotes appear. 89%—Plants first invade land. 99.9%—Human and ape ancestries diverge! 2. Students might need to be reminded about the reactive properties of oxygen. Note that rust is the result of oxygen interacting with iron. Oxygen is highly reactive and could interfere with life-forming chemical processes today.

Humans Coloniz of land ation Animals Multi eukar cellular yotes
Origin of solar system and Earth Pre sent 1 4 Sing eukar cel yotes le- led kary otes Pro Figure 15.2 A clock analogy for the major events in the history of life on Earth Bil ars ons of ago ye li 2 3 Atmo oxy sphe ric gen Figure 15.2

THE ORIGIN OF LIFE We may never know for sure how life on Earth began.
Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Resolving the Biogenesis Paradox
All life today arises by the reproduction of preexisting life, or biogenesis. If this is true, how could the first organisms arise? From the time of the ancient Greeks until well into the 19th century, it was commonly believed that life regularly arises from nonliving matter, an idea called spontaneous generation. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Today, most biologists think it is possible that life on early Earth produced simple cells by chemical and physical processes. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Figure 15.3 An artist's rendition of Earth about 3 billion years ago

A Four-Stage Hypothesis for the Origin of Life
According to one hypothesis, the first organisms were products of chemical evolution in four stages. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Stage 1: Abiotic Synthesis of Organic Monomers
The first stage in the origin of life has been the most extensively studied by scientists in the laboratory. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

The Process of Science: Can Biological Monomers Form Spontaneously?
Observation: Modern biological macromolecules are all composed of elements that were present in abundance on the early Earth. Question: Could biological molecules arise spontaneously under conditions like those on the early Earth? Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.) © 2010 Pearson Education, Inc.

Prediction: Organic molecules would form and accumulate.
Hypothesis: A closed system designed in the laboratory to simulate early Earth conditions could produce biologically important organic molecules from inorganic ingredients. Prediction: Organic molecules would form and accumulate. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Experiment: An apparatus was built to mimic the early Earth atmosphere and included
Hydrogen gas (H2), methane (CH4), ammonia (NH3), and water vapor (H2O) Sparks, discharged into the chamber to mimic the prevalent lightning of the early Earth A condenser to cool the atmosphere, causing water and dissolved compounds to “rain” into the miniature “sea” Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Figure 15.4 CH4 “Atmosphere” Water vapor NH3 H2 Electrode Condenser
Cold water Cooled water containing organic molecules H2O Figure 15.4 The abiotic production of organic molesules: A laboratory simulation of early-Earth chemistry Stanley Miller re-creating his 1953 experiment “Sea” Sample for chemical analysis Miller and Urey’s experiment Figure 15.4

Results: After the apparatus had run for a week, an abundance of organic molecules essential for life had collected in the “sea,” including amino acids, the monomers of proteins. Since Miller and Urey’s experiments, laboratory analogues of the primeval Earth have produced All 20 amino acids Several sugars Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Stage 2: Abiotic Synthesis of Polymers
Researchers have brought about the polymerization of monomers to form polymers, such as proteins and nucleic acids, by dripping solutions of organic monomers onto Hot sand Clay Rock Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Stage 3: Formation of Pre-Cells
A key step in the origin of life was the isolation of a collection of abiotically created molecules within a membrane. Laboratory experiments demonstrate that pre-cells could have formed spontaneously from abiotically produced organic compounds. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Such pre-cells produced in the laboratory display some lifelike properties. They:
Have a selectively permeable surface Can grow by absorbing molecules from their surroundings Swell or shrink when placed in solutions of different salt concentrations Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Stage 4: Origin of Self-Replicating Molecules
Life is defined partly by the process of inheritance, which is based on self-replicating molecules. One hypothesis is that the first genes were short strands of RNA that replicated themselves without the assistance of proteins, perhaps using RNAs that can act as enzymes, called ribozymes. Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

Original “gene” Complementary RNA chain Figure 15.5
Figure 15.5 Self-replication of RNA "genes" Figure 15.5

From Chemical Evolution to Darwinian Evolution
Over millions of years Natural selection favored the most efficient pre-cells The first prokaryotic cells evolved Student Misconceptions and Concerns 1. Students might not have considered that cells today are not “created from scratch.” Unlike the way a cake is prepared, or an automobile is constructed, life today is not known to form by the assembly of raw materials into cells. Point out that the process of piecemeal building, so common in our lives, is not a part of cellular biology. 2. Students may think that scientists have answers for all of life’s questions. Thus, they may appreciate knowing that many questions are inappropriate for science. Matters of aesthetics, morals, and political issues are often addressed by other methods of thinking. Questions such as: “Was Picasso a better artist than Rembrandt?” “What should we do about homeless people?” and “Should abortion be illegal?” are examples. This might be a good time to further distinguish between the process of science and other ways of knowing. Teaching Tips 1. Consider pointing out the logic of spontaneous generation given the knowledge at the time. Piles of manure and rotting flesh left in the open would apparently produce flies. At that time little was understood about eggs, sperm, and fertilization, making spontaneous generation a logical conclusion. 2. This four-stage hypothesis for the origin of life is a little like 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 these principles before addressing the stages. 3. The inherent property of bipolar molecules such as phospholipids, to naturally form double membranes or micelles, is worth discussing with your class. Because of these properties, membranes naturally heal as the hydrophobic phospholipid tails and polar heads align. 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 we have life. Are self-replicating, RNA-based, membrane-bound structures alive? This discussion of the evolution of the first cells helps us better understand our definition of life. 5. Much of the remaining chapter is descriptive of the traits and habits of single-celled prokaryotes and eukaryotes. Students might benefit by developing a series of charts that allow them to quickly review the properties of various subgroups. (For example, the shapes of bacteria, the major modes of nutrition, and the various subgroups.)

PROKARYOTES Prokaryotes lived and evolved all alone on Earth for 2 billion years before eukaryotes evolved. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

They’re Everywhere! Prokaryotes Are found wherever there is life
Far outnumber eukaryotes Can cause disease Can be beneficial Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Prokaryotes live deep within the Earth and in habitats too cold, too hot, too salty, too acidic, or too alkaline for any eukaryote to survive. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Compared to eukaryotes, prokaryotes are
Much more abundant Typically much smaller Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Colorized SEM Figure 15.7 Bacteria on the head of a pin Figure 15.7

Prokaryotes Are ecologically significant, recycling carbon and other vital chemical elements back and forth between organic matter, the soil, and atmosphere Cause about half of all human diseases Are more typically benign or beneficial Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

The Structure and Function of Prokaryotes
Prokaryotic cells Lack true nuclei Lack other membrane-enclosed organelles Have cell walls exterior to their plasma membranes Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Figure 4.4 Plasma membrane (encloses cytoplasm) Cell wall (provides
Rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Figure 4.4 An idealized prokaryotic cell Pili (attachment structures) Colorized TEM Figure 4.4

Figure 4.5 Ribosomes Centriole Not in most plant cells Cytoskeleton
Lysosome Flagellum Plasma membrane Nucleus Mitochondrion Rough endoplasmic reticulum (ER) Smooth endoplasmic reticulum (ER) Golgi apparatus Idealized animal cell Cytoskeleton Mitochondrion Central vacuole Nucleus Not in animal cells Cell wall Rough endoplasmic reticulum (ER) Figure 4.5 A view of an idealized animal cell and plant cell Chloroplast Ribosomes Plasma membrane Smooth endoplasmic reticulum (ER) Channels between cells Idealized plant cell Golgi apparatus Figure 4.5

Procaryotic Forms Prokaryotes come in several shapes:
Spherical (cocci) Rod-shaped (bacilli) Spiral Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

SHAPES OF PROKARYOTIC CELLS
Spherical (cocci) Rod-shaped (bacilli) Spiral Colorized SEM Colorized SEM Colorized TEM Figure 15.8 Three common shapes of prokaryotic cells Figure 15.8

Most prokaryotes are Some prokaryotes Unicellular Very small
Form true colonies Show specialization of cells Are very large Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

(a) Actinomycete (b) Cyanobacteria (c) Giant bacterium LM LM
Colorized SEM (a) Actinomycete (b) Cyanobacteria (c) Giant bacterium Figure 15.9 A diversity of prokayotic shapes and sizes. Figure 15.9

About half of all prokaryotes are mobile, using flagella.
Many have one or more flagella that propel the cells away from unfavorable places or toward more favorable places, such as nutrient-rich locales. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Flagellum Plasma membrane Cell wall Rotary movement of each flagellum
Colorized TEM Flagellum Plasma membrane Figure Prokaryotic flagella Cell wall Rotary movement of each flagellum Figure 15.10

Procaryotic Reproduction
Most prokaryotes can reproduce by binary fission and at very high rates if conditions are favorable. Some prokaryotes Form endospores, thick-coated, protective cells that are produced within the cells when they are exposed to unfavorable conditions Can survive very harsh conditions for extended periods, even centuries Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Endospore Colorized SEM Figure 15.11
Figure An endopsore in an anthrax bacterium Figure 15.11

Procaryotic Nutrition
Prokaryotes exhibit four major modes of nutrition. Phototrophs obtain energy from light. Chemotrophs obtain energy from environmental chemicals. Species that obtain carbon from carbon dioxide (CO2) are autotrophs. Species that obtain carbon from at least one organic nutrient—the sugar glucose, for instance—are called heterotrophs. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

We can group all organisms according to the four major modes of nutrition if we combine the
Energy source (phototroph versus chemotroph) and Carbon source (autotroph versus heterotroph) Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Figure 15.12 MODES OF NUTRITION Energy source Light Chemical
Photoautotrophs Chemoautotrophs Colorized TEM CO2 Elodea, an aquatic plant Bacteria from a hot spring Carbon source Photoheterotrophs Chemoheterotrophs Colorized TEM Figure Modes of nutrition Organic compounds Rhodopseudomonas Little Owl (Athene noctua) Figure 15.12

The Two Main Branches of Prokaryotic Evolution: Bacteria and Archaea
By comparing diverse prokaryotes at the molecular level, biologists have identified two major branches of prokaryotic evolution: Bacteria Archaea (more closely related to eukaryotes) Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception. © 2010 Pearson Education, Inc.

Some archaea are “extremophiles.”
Halophiles thrive in salty environments. Thermophiles inhabit very hot water. Methanogens inhabit the bottoms of lakes and swamps and aid digestion in cattle and deer. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

(a) Salt-loving archaea (b) Heat-loving archaea
Figure Archaeal "extremophiles" (a) Salt-loving archaea (b) Heat-loving archaea Figure 15.13

Bacteria and Humans Bacteria interact with humans in many ways.
Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Bacteria That Cause Disease
Bacteria and other organisms that cause disease are called pathogens. Most pathogenic bacteria produce poisons. Exotoxins are poisonous proteins secreted by bacterial cells. Endotoxins are not cell secretions but instead chemical components of the outer membrane of certain bacteria. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Haemophilus Cells of nasal influenzae lining Colorized SEM
Figure Bacteria that cause pneumonia Haemophilus influenzae Cells of nasal lining Figure 15.14

The best defenses against bacterial disease are
Sanitation Antibiotics Education Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Lyme disease is Caused by bacteria carried by ticks
Treated with antibiotics, if detected early Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Lyme disease bacterium
SEM Figure Lyme disease, a bacterial disease transmitted by ticks Tick that carries the Lyme disease bacterium Spirochete that causes Lyme disease “Bull’s-eye” rash Figure 15.15

Bioterrorism Humans have a long and ugly history of using organisms as weapons. During the Middle Ages, armies hurled the bodies of plague victims into enemy ranks. Early conquerors, settlers, and warring armies in South and North America gave native peoples items purposely contaminated with infectious bacteria. In 1984, members of a cult in Oregon contaminated restaurant salad bars with Salmonella bacteria. In the fall of 2001, five Americans died from the disease anthrax in a presumed terrorist attack. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Figure 15.16 Cleaning up after a bioterrorist attack

The Ecological Impact of Prokaryotes
Pathogenic bacteria are in the minority among prokaryotes. Far more common are species that are essential to our well-being, either directly or indirectly. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Prokaryotes and Chemical Recycling
Prokaryotes play essential roles in Chemical cycles in the environment The breakdown of organic wastes and dead organisms Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Prokaryotes and Bioremediation
Bioremediation is the use of organisms to remove pollutants from Water Air Soil A familiar example is the use of prokaryotic decomposers in sewage treatment. Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Rotating spray arm Rock bed coated with aerobic prokaryotes and fungi
Figure Putting microbes to work in sewage treatment facilities Outflow Liquid wastes Figure 15.17

Certain bacteria Can decompose petroleum
Are useful in cleaning up oil spills Student Misconceptions and Concerns 1. Students might think of evolution as a progression, with multicellular eukaryotes somehow fundamentally better than prokaryotes. The recognition of the enduring existence of prokaryotes nearly 2 billion years older than eukaryotes and the tremendous diversity of prokaryotic lifestyles might clarify the misperception of “evolutionary improvement”. After all, what eukaryotes can survive in the habitats of extremophiles? 2. Some students might equate the term “bacteria” with “prokaryotes.” A discussion of the domains archaea and bacteria will help with this distinction. 3. Many people expect that hand washing and the use of soaps leaves the washed parts bacteria free. The tremendous numbers of bacteria that normally remain and routinely reside on and within our bodies is little appreciated. 4. Students might easily be led to believe that we have already documented the diversity of life on Earth. However, by most estimates, we have identified fewer than 10% of the suspected species of eukaryotes. The ongoing discovery of the diversity of prokaryotes humbles microbiologists working today. The diversity of prokaryotic life may very well be beyond human determination. Teaching Tips 1. Bacteria and archaea live within the hot springs of Yellowstone National Park. The pigments in these microbes give color to the springs. A Google Image search using the key words “Yellowstone hot springs color” will quickly identify photographic resources revealing extremophile diversity. 2. Consider referring to This website is a free, and detailed, microbiology textbook on the Internet. It is an excellent reference for instructors lacking extensive training in microbiology. 3. Some modeling clay (oil-based never dries out) and toothpicks can be used to make some quick and easy visual aids to demonstrate the various shapes of these bacteria for lecture. The construction of these diverse shapes might also make for a quick lab activity. 4. Exponential growth might be related to your class with the question “Would you rather have a million dollars or start out with just a penny and have it doubled every day for a month?” Choosing the doubling amount pays off in about 10 million dollars. 5. The chapter section about the ecological impact of prokaryotes contains many topics that are of great interest to most students. Consider making a short Internet assignment. Each student could identify a recent article or website that addresses one or more of these subtopics (e.g., exotoxins, endotoxins, bioremediation, etc.). They could write a short summary or the website address to you, for your inspection. 6. Chemoautotrophs permit ecosystems, which do not rely upon sunlight for a source of metabolic energy (though the Earth would quickly freeze solid without the sun!). Students may have been taught that all ecosystems are based upon photosynthesis. Chemoautotrophs reveal an exception.

Figure 15.18 Treatment of an oil spill in Alaska

PROTISTS Protists Are eukaryotic Evolved from prokaryotic ancestors
Are ancestral to all other eukaryotes, which are Plants Fungi Animals Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Figure 15.19 A diversity of protists in a drop of pond water

The Origin of Eukaryotic Cells
Eukaryotic cells evolved by The infolding of the plasma membrane of a prokaryotic cell to form the endomembrane system and Endosymbiosis, one species living inside another host species, in which free-living bacteria came to reside inside a host cell, producing mitochondria and chloroplasts Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Plasma membrane Photosynthetic prokaryote DNA Cytoplasm Membrane infolding (Some cells) Endosymbiosis Aerobic heterotrophic prokaryote Ancestral prokaryote Endoplasmic reticulum Chloroplast Nucleus Nuclear envelope Mitochondrion Figure A two-stage hypothesis for the evolution of eukaryotes through endosymbiosis Cell with nucleus and endomembrane system Photosynthetic eukaryotic cell (a) Origin of the endomembrane system (b) Origin of mitochondria and chloroplasts Figure 15.20

The Diversity of Protists
Protists can be Unicellular Multicellular More than any other group, protists vary in Structure Function Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Protists are not one distinct group but instead represent all the eukaryotes that are not plants, animals, or fungi. Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

The classification of protists remains a work in progress.
The four major categories of protists, grouped by lifestyle, are Protozoans Slime molds Unicellular algae Seaweeds Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Protozoans Protists that live primarily by ingesting food are called protozoans. Protozoans with flagella are called flagellates and are typically free-living, but sometimes are nasty parasites. Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

A flagellate: Giardia Colorized SEM Figure 15.21a
Figure 15.21a A diversity of protozoans Colorized SEM A flagellate: Giardia Figure 15.21a

Another flagellate: trypanosomes
Figure 15.21b A diversity of protozoans Colorized SEM Another flagellate: trypanosomes Figure 15.21b

Amoebas are characterized by
Great flexibility in their body shape The absence of permanent organelles for locomotion Most species move and feed by means of pseudopodia (singular, pseudopodium), temporary extensions of the cell. Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Amoebas may have a shell, as seen in forams, or no shell at all.
Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Figure 15.21c A diversity of protozoans
LM An amoeba Figure 15.21c

Figure 15.21d A diversity of protozoans
LM A foram Figure 15.21d

Apicomplexans are Named for a structure at their apex (tip) that is specialized for penetrating host cells and tissues All parasitic, such as Plasmodium, which causes malaria Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

An apicomplexan TEM Figure 15.21e
Figure 15.21e A diversity of protozoans TEM An apicomplexan Figure 15.21e

Ciliates Are mostly free-living (nonparasitic), such as the freshwater ciliate Paramecium Use structures called cilia to move and feed Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Figure 15.21f A diversity of protozoans
LM A ciliate Figure 15.21f

Figure 15.21 Food being ingested Pseudopodium of amoeba Colorized SEM
LM A flagellate: Giardia Another flagellate: trypanosomes An amoeba Apical complex Cilia Figure A diversity of protozoans Oral groove Red blood cell LM TEM LM A foram An apicomplexan A ciliate Figure 15.21

Slime Molds Slime molds resemble fungi in appearance and lifestyle, but the similarities are due to convergence, and slime molds are not at all closely related to fungi. The two main groups of these protists are Plasmodial slime molds Cellular slime molds Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Plasmodial slime molds
Can be large Are decomposers on forest floors Are named for the feeding stage in their life cycle, an amoeboid mass called a plasmodium Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Figure 15.22 A plasmodial slime mold

Cellular slime molds have an interesting and complex life cycle that changes between a
Feeding stage of solitary amoeboid cells Sluglike colony that moves and functions as a single unit Stalklike reproductive structure Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Slug-like colony Amoeboid cells Reproductive structure LM Figure 15.23
Figure Life stages of a cellular slime mold Reproductive structure Figure 15.23

Unicellular and Colonial Algae
Algae are Photosynthetic protists Found in plankton, the communities of mostly microscopic organisms that drift or swim weakly in aquatic environments Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Unicellular algae include
Diatoms, which have glassy cell walls containing silica Dinoflagellates, with two beating flagella and external plates made of cellulose Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

(a) A dinoflagellate, with its wall of protective plates
Figure 15.24a Unicellular and colonial algae SEM (a) A dinoflagellate, with its wall of protective plates Figure 15.24a

(b) A sample of diverse diatoms, which have glossy walls
Figure 15.24b Unicellular and colonial algae LM (b) A sample of diverse diatoms, which have glossy walls Figure 15.24b

Green algae are Unicellular
Sometimes flagellated, such as Chlamydomonas Colonial, sometimes forming a hollow ball of flagellated cells, as seen in Volvox Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

(c) Chlamydomonas, a unicellular green alga with a pair of flagella
Figure 15.24c Unicellular and colonial algae Colorized SEM (c) Chlamydomonas, a unicellular green alga with a pair of flagella Figure 15.24c

(d) Volvox, a colonial green alga
Figure 15.24d Unicellular and colonial algae LM (d) Volvox, a colonial green alga Figure 15.24d

Seaweeds Seaweeds Are only similar to plants because of convergent evolution Are large, multicellular marine algae Grow on or near rocky shores Are often edible Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Seaweeds are classified into three different groups, based partly on the types of pigments present in their chloroplasts: Green algae Red algae Brown algae (including kelp) Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Green algae Red algae Brown algae Figure 15.25
Figure The three major groups of seaweeds Red algae Brown algae Figure 15.25

Evolution Connection: The Origin of Multicellular Life
Multicellular organisms have interdependent, specialized cells that perform different functions, such as feeding, waste disposal, gas exchange, and protection—and are dependent on each other. Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships. © 2010 Pearson Education, Inc.

Colonial protists likely formed the evolutionary links between unicellular and multicellular organisms. Student Misconceptions and Concerns 1. Students may need to be reminded that most prokaryotes are about a tenth the diameter of eukaryotic cells. Thus, by the process of endosymbiosis, symbiotic bacteria could easily fit within larger eukaryotic cells. 2. Students might think of protists as simple systems. However, as the authors note, within a single cell protists must carry out all the basic functions performed by the set of specialized cells that collectively form the bodies of plants and animals. Teaching Tips 1. The extensive diversity of protists permits endless opportunities for students to select an example of a protist and report on it in some way. For example, students can sketch “their protist,” find web resources, and/or plot its position in a classification of protists. These short exercises in content “ownership” allow students to develop a greater depth of understanding and increase interaction with the subject. 2. Mitochondrial DNA is widely used to analyze evolutionary relationships. Challenge students to explain why mitochondrial DNA might be better than nuclear DNA to trace these relationships.

Figure 15.26-3 Unicellular protist Gamete Food-synthesizing Somatic
cells Somatic cells Locomotor cells Colony Figure A model for the evolution of multicellular organisms from unicellular protists. (Step 3) Early multicellular organism with specialized, interdependent cells Later organism with gametes and somatic cells Figure

The Evolution of Microbial Life

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