3. Chapter: Exploring and Classifying Life Table of Contents Section 3: Where does life come from?Where does life come from? Section 1: What is science? Section 2: Living ThingsLiving Things Section 4: How are living things classified?How are living things classified?

4. Asking questions is one way scientists find out about anything in the world and the universe. Science is often described as an organized way of studying things and finding answers to questions. The Work of Science What is science? 1 1

5. Many types of science exist. Types of Science What is science? 1 1 Life scientist might study any of the millions of difference animals, plants, and other living things on Earth. Life scientists who study plants are botanists, and those who study animals are zoologists.

6. Suppose your CD player stops playing music. To figure out what happened, you have to think about it. That’s called critical thinking. Critical Thinking What is science? 1 1 You separate important information from unimportant information—that’s a skill. Identifying the problem is another skill you have.

7. Besides critical thinking, solving a problem requires organization. Solving Problems What is science? 1 1 In science, this organization often takes the form of a series of procedures called scientific methods.

8. Solving Problems What is science? 1 1

9. A control is the standard to which the outcome of a test is compared. Controls What is science? 1 1 A variable is something in an experiment that can change. An experiment should have only one variable.

10. When using scientific methods, it is important to share information. Report Results What is science? 1 1 In science it is important to explain how an experiment can be made better if it is done again.

11. After scientists report the results of experiments supporting their hypotheses, the results can be used to propose a scientific theory. Developing Theories What is science? 1 1 A scientific theory is an explanation of things or events based on scientific knowledge that is the result of many observations and experiments. It is not a guess or someone’s opinion.

12. Theory is if data collected from several experiments over a period of time all support the hypothesis. Developing Theories What is science? 1 1

13. A valid theory raises many new questions. Developing Theories What is science? 1 1 Data or information from new experiments might change conclusions and theories can change.

14. A scientific law is a statement about how things work in nature that seems to be true all the time. Laws What is science? 1 1 They are less likely to change than theories. Laws tell you what will happen under certain conditions but do not necessarily explain why it happened.

15. You can use scientific methods to answer all sorts of questions. Scientific Methods Help Answer Questions What is science? 1 1 Using scientific methods does not guarantee that you will get an answer. Often scientific methods just lead to more questions and more experiments.

16. An important part of most scientific investigations is making accurate measurements. Measuring with Scientific Units What is science? 1 1

17. Measuring with Scientific Units What is science? 1 1 You will use the same standard system of measurement scientists use. This system is called the International System of Units, or SI.

18. Laboratory safety is important. Safety First What is science? 1 1 In many states, a student can participate in a laboratory class only when wearing proper eye protection. Following safety rules will protect you and others from injury during your lab experiences. Click image to view movie.

19. 1 1 Section Check Question 1 This diagram shows a way to use scientific methods to solve a problem. According to the diagram, if a hypothesis is not supported by data then you should _______.

20. 1 1 Section Check A. change the data so that they do support the hypothesis B. find a different problem to solve C. propose a scientific theory D. revise the hypothesis and perform new experiments

21. 1 1 Section Check Answer The correct answer is D. Scientific methods are an organized way to solve a problem in science. This series of procedures involves forming a hypothesis that can be tested.

22. 1 1 Section Check Question 2 What is the definition of a control in a scientific experiment? Answer A control is the standard to which the outcome of a test will be compared. Controls help you determine how to interpret your data.

23. 1 1 Section Check Question 3 A statement about how things work in nature that seems to be true all the time is a _______. A. conclusion B. hypothesis C. law D. variable

24. 1 1 Section Check Answer The correct answer is C. Although laws can be modified as more information becomes known, they are less likely to change than theories.

25. What are living things like? What does it mean to be alive? Any living thing is called an organism. They have different behaviors and food needs. In spite of these differences, all organisms have similar traits. Living Things 2 2

26. Living Things Are Organized A cell is the smallest unit of an organism that carries on the functions of life. Cells take in materials from their surroundings and use them in complex ways. Each cell has an orderly structure and contains hereditary material. Living Things 2 2 The hereditary material contains instructions for cellular organization and function.

27. Living Things Respond Living things interact with their surrounds. Anything that causes some change in an organism is a stimulus (plural, stimuli). Living Things 2 2 The reaction to a stimulus is a response. Often that response results in movement.

28. Living Things Respond Living things also respond to stimuli that occur inside them. Living Things 2 2 An organism’s ability to keep the proper conditions inside no matter what is going on outside the organism is called homeostasis. Homeostasis is a trait of all living things.

29. Living Things Use Energy The energy used by most organisms comes either directly or indirectly from the Sun. Living Things 2 2 Plants and some other organisms use the Sun’s energy and the raw materials carbon dioxide and water to make food.

30. Living Things Use Energy You and most other organisms can’t use the energy of sunlight directly. Instead, you take in and use food as a source of energy. Living Things 2 2

31. Living Things Use Energy Some bacteria live at the bottom of the oceans and in other areas where sunlight cannot reach. Living Things 2 2 They can’t use the Sun’s energy to produce food. Instead, the bacteria use energy stored in some chemical compounds and the raw material carbon dioxide to make food.

32. Living Things Grow and Develop Growth of many-celled organisms is mostly due to an increase in the number of cells. Living Things 2 2 In one-celled organisms, growth is due to an increase in the size of the cell. Organisms change as they grow. All of the changes that take place during the life of an organism are called development.

33. Living Things Reproduce Living things reproduce themselves in many different ways. Living Things 2 2 Cats, dogs, alligators, fish, birds, bees, and trees eventually reproduce. Beetles, like most insects, reproduce by laying eggs.

34. Living Things Reproduce Without reproduction, living things would not exist to replace those individuals that die. Living Things 2 2 An individual cat can live its entire life without reproducing. However, if cats never reproduced, all cats soon would disappear.

35. What do living things need? To survive, all living things need a place to live and raw materials. Living Things 2 2 The raw materials that they require and the exact place where they live can vary.

36. A Place to Live The environment limits where organisms can live. Living Things 2 2 Not many kinds of organisms can live in extremely hot or extremely cold environments. Most cannot live at the bottom of the ocean or on the tops of mountains. An organism’s surroundings must provide for all of its needs.

37. Raw Materials Water is important for all living things. Living Things 2 2 Plants and animals take in and give off large amounts of water each day. Most organisms are composed of more than 50 percent water. You are made of 60 to 70 percent water.

38. Raw Materials Living things are made up of substance such as proteins, fats, and sugars. Living Things 2 2 Animals take in most of these substances from the foods they eat. Plants and some bacteria make them using raw materials from their surroundings.

39. Raw Materials When organisms die, substances in their bodies are broken down and released into the soil or air. Living Things 2 2 The substances can then be used again by other living organisms.

40. 2 2 Section Check Question 1 What is the smallest unit in a cat that carries on the functions of life? Answer The cell is the smallest unit. All organisms are composed of cells. Cells take in materials from their surroundings and use them in complex ways.

41. 2 2 Section Check Question 2 Pulling your hand back when you accidentally touch a hot pan on the stove is an example of what characteristic of living things? A. growth and development B. organization C. reproduction D. response to stimuli

42. 2 2 Section Check Answer The correct answer is D. The hot pan is an example of a stimulus. Living things can respond to both external and internal stimuli.

43. 2 2 Section Check Question 3 Give an example of two raw materials that you need to survive. Answer Some possible answers include: water, food, and oxygen. Some bacteria and plants can make food from raw materials in their surroundings.

44. Life Comes from Life Before the seventeenth century, some people thought that insects and fish came from mud, that earthworms fell from the sky when it rained, and that mice came from grain. The idea that living things come from nonliving things is known as spontaneous generation. Where does life come from? 3 3 This idea became a theory that was accepted for several hundred years.

45. Spontaneous Generation and Biogenesis From the late seventeenth century through the middle of the eighteenth century, experiments were done to test the theory of spontaneous generation. Where does life come from? 3 3

46. Spontaneous Generation and Biogenesis Louis Pasteur provided in mid 1800’s disproved the theory of spontaneous generation. Where does life come from? 3 3 SG was replaced with biogenesis (bi oh JE nuh suss), which is the theory that living things come only from other living things.

47. Life’s Origins If living things can come only from other living things, how did life on Earth begin? Where does life come from? 3 3 Some scientists hypothesize that about 5 billion years ago, Earth’s solar system was a whirling mass of gas and dust. They hypothesize that the Sun and planets were formed from this mass.

48. Oparin’s Hypothesis In 1924 Alexander I. Oparin suggested that Earth’s early atmosphere had no oxygen but was made up of the gases ammonia, hydrogen, methane, and water vapor. Where does life come from? 3 3 Oparin hypothesized that these gases could have combined to form the more complex compounds found in living things.

49. Oparin’s Hypothesis American scientists Stanley L. Miller and Harold Urey set up an experiment to test Oparin’s hypothesis in 1953. Where does life come from? 3 3 Although the Miller-Urey experiment showed that chemicals found in living things could be produced, it did not prove that life began in this way.

50. 3 3 Section Check This diagram shows an experiment Louis Pasteur conducted with boiled broth and S-necked flasks. Why did microbes only grow in the bottom flask? Question 1

51. 3 3 Section Check Microbes from the air settled out at the bottom of the S-neck and only entered the broth when it was tilted so that the broth touched this area. This experiment by Pasteur helped disprove the theory of spontaneous generation. Answer

52. 3 3 Section Check Which one of the following examples supports the theory of biogenesis? Question 2 A. kittens are produced from cats B. milk is produced by cows C. rain is produced by rain clouds D. stimuli produce responses

53. 3 3 Section Check The correct answer is A. The theory of biogenesis states that living things come only from other living things. Answer

54. 3 3 Section Check What did Alexander Oparin suggest about Earth’s early atmosphere? Question 3

55. 3 3 Section Check He suggested that it contained no oxygen but was made up of the gases ammonia, hydrogen, methane, and water vapor. He hypothesized that these gases could have combined to produce compounds found in living things. Answer

56. Classification Libraries group similar types of books together. When you place similar items together, you classify them. How are living things classified? 4 4 Organisms also are classified into groups.

57. History of Classification Early classifications included grouping plants that were used in medicines. Animals were often classified by human traits such as courageous—for lions—or wise—for owls. How are living things classified? 4 4

58. History of Classification More than 2,000 years ago, a Greek named Aristotle observed living things. He decided that any organism could be classified as either a plant or an animal. How are living things classified? 4 4 Then he broke these two groups into smaller groups. Animal categories included hair or no hair, four legs or few legs, and blood or no blood.

59. Linnaeus Carolus Linnaeus developed a new system of grouping organisms. His classification system was based on looking for organisms with similar structures. For example, plants that had similar flower structure were grouped together. How are living things classified? 4 4

60. Modern Classification Modern scientists use similarities in structure to classify organisms. They also use similarities in both external and internal features. Specific characteristics at the cellular level can be used to infer the degree of relatedness among organisms. How are living things classified? 4 4

61. Modern Classification In addition, scientists study fossils, hereditary information, and early stages of development. They use all of this information to determine an organism’s phylogeny. How are living things classified? 4 4 Phylogeny (fi LAH juh nee) is the evolutionary history of an organism, or how it has changed over time.

62. Six Kingdoms A kingdom is the first and largest category. Organisms are placed into kingdoms based on various characteristics. How are living things classified? 4 4

63. Six Kingdoms How are living things classified? 4 4 The smallest classification category is a species. Organisms that belong to the same species can mate and produce fertile offspring.

64. Scientific Names What would happen if life scientists used only common names of organisms when they communicated with other scientists? Many misunderstandings would occur, and sometimes health and safety are involved. How are living things classified? 4 4 A naming system developed by Linnaeus helped solve this problem. It gave each species a unique, two-word scientific name.

65. Binomial Nomenclature The two-word naming system that Linnaeus used to name the various species is called binomial nomenclature (bi NOH mee ul. NOH mun klay chur). How are living things classified? 4 4 It is the system used by modern scientists to name organisms.

66. Binomial Nomenclature The first word of the two-word name identifies the genus of the organism. How are living things classified? 4 4 A genus is a group of similar species. The second word of the name might tell you something about the organism— what it looks like, where it is found, or who discovered it.

67. Uses of Scientific Names Two-word scientific names are used for four reasons. How are living things classified? 4 4 First, they help avoid mistakes. Second, organisms with similar evolutionary histories are classified together. Third, scientific names give descriptive information about the species. Fourth, scientific names allow information about organisms to be organized easily and efficiently.

68. Tools for Identifying Organisms Tools used to identify organisms include field guides and dichotomous (di KAH tuh mus) keys. How are living things classified? 4 4 Many different field guides are available. Most have descriptions and illustrations of organisms and information about where each organism lives. You can identify species from around the world using the appropriate field guide.

69. Dichotomous Keys A dichotomous key is a detailed list of identifying characteristics that includes scientific names. How are living things classified? 4 4 Dichotomous keys are arranged in steps with two descriptive statements at each step.

70. 4 4 Section Check Question 1 Over 2,000 years ago, Aristotle developed a system to classify all organisms _______. A. as either plant or animal. B. based on fossils. C. into six different kingdoms. D. using binomial nomenclature.

71. 4 4 Section Check Answer The correct answer is A. Aristotle broke these two groups into smaller groups. Two of his smaller groups of animals would have been animals with hair and those with no hair.

72. 4 4 Section Check Question 2 What word is used to describe the evolutionary history of an organism? Answer The word is phylogeny. Phylogeny explains how an organism has changed over time and is the basis for the modern classification of many organisms.

73. 4 4 Section Check Question 3 Acer rubrum is the scientific name for a red maple tree. This name is an example of _______. A. a dichotomous key B. a hypothesis C. binomial nomenclature D. spontaneous generation

74. 4 4 Section Check Answer The correct answer is C. Binomial nomenclature is the system used by modern scientists to name organisms. The first part of the scientific name identifies the genus of the organism.

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