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

3. What is science? 1
The Work of Science
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.

4. Types of Science 1 Many types of science exist.
What is science? 1
Types of Science
Many types of science exist.
For example, energy and matter have a relationship. That’s a topic for physics.
On the other hand, a 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.

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

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

7. What is science? 1
Solving Problems

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

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

10. What is science? 1
Developing Theories
After scientists report the results of experiments supporting their hypotheses, the results can be used to propose a scientific theory.
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.

11. What is science? 1
Developing Theories
If data collected from several experiments over a period of time all support the hypothesis, it finally can be called a theory.

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

13. What is science? 1
Laws
A scientific law is a statement about how things work in nature that seems to be true all the time.
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.

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

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

16. Measuring with Scientific Units
What is science? 1
Measuring with Scientific Units
You will use the same standard system of measurement scientists use to communicate and understand each other’s research and results. This system is called the International System of Units, or SI.

17. Safety First 1 Laboratory safety is important.
What is science? 1
Safety First
Laboratory safety is important.
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.
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18. Section Check 1
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 _______.

19. B. find a different problem to solve C. propose a scientific theory
Section Check 1
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

20. Section Check 1
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.

21. Section Check 1
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.

22. Section Check 1
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

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

24. What are living things like?2
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.

25. Living Things Are Organized2
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.
The hereditary material contains instructions for cellular organization and function.

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

27. Living Things 2
Living Things Respond
Living things also respond to stimuli that occur inside them.
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.

28. Living Things Use Energy2
Living Things Use Energy
The energy used by most organisms comes either directly or indirectly from the Sun.
Plants and some other organisms use the Sun’s energy and the raw materials carbon dioxide and water to make food.

29. Living Things Use Energy2
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.

30. Living Things Use Energy2
Living Things Use Energy
Some bacteria live at the bottom of the oceans and in other areas where sunlight cannot reach.
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.

31. Living Things Grow and Develop2
Living Things Grow and Develop
Growth of many-celled organisms is mostly due to an increase in the number of cells.
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.

32. Living Things Reproduce2
Living Things Reproduce
Cats, dogs, alligators, fish, birds, bees, and trees eventually reproduce.
Living things reproduce themselves in many different ways.
Beetles, like most insects, reproduce by laying eggs.

33. Living Things Reproduce2
Living Things Reproduce
Without reproduction, living things would not exist to replace those individuals that die.
An individual cat can live its entire life without reproducing. However, if cats never reproduced, all cats soon would disappear.

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

35. A Place to Live 2 The environment limits where organisms can live.
Living Things 2
A Place to Live
The environment limits where organisms can live.
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.

36. Raw Materials 2 Water is important for all living things.
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.

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

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

39. Section Check 2
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.

40. Section Check 2
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

41. Section Check 2
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.

42. Section Check 2
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.

43. Where does life come from?3
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.
This idea became a theory that was accepted for several hundred years.

44. Spontaneous Generation and Biogenesis
Where does life come from? 3
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.

45. Spontaneous Generation and Biogenesis
Where does life come from? 3
Spontaneous Generation and Biogenesis
It was not until the mid 1800s that the work of Louis Pasteur provided enough evidence to disprove the theory of spontaneous generation.
It was replaced with biogenesis (bi oh JE nuh suss), which is the theory that living things come only from other living things.

46. Where does life come from?3
Life’s Origins
If living things can come only from other living things, how did life on Earth begin?
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.

47. Where does life come from?3
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.
Oparin hypothesized that these gases could have combined to form the more complex compounds found in living things.

48. Where does life come from?3
Oparin’s Hypothesis
American scientists Stanley L. Miller and Harold Urey set up an experiment to test Oparin’s hypothesis in 1953.
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.

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

50. Section Check 3
Answer
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.

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

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

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

54. Section Check 3
Answer
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.

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

56. History of Classification
How are living things classified? 4
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.

57. History of Classification
How are living things classified? 4
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.
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.

58. How are living things classified?4
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.

59. Modern Classification
How are living things classified? 4
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.

60. Modern Classification
How are living things classified? 4
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.
Phylogeny (fi LAH juh nee) is the evolutionary history of an organism, or how it has changed over time.

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

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

63. How are living things classified?4
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.
A naming system developed by Linnaeus helped solve this problem. It gave each species a unique, two-word scientific name.

64. Binomial Nomenclature
How are living things classified? 4
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).
It is the system used by modern scientists to name organisms.

65. Binomial Nomenclature
How are living things classified? 4
Binomial Nomenclature
The first word of the two-word name identifies the genus of the organism.
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.

66. Uses of Scientific Names
How are living things classified? 4
Uses of Scientific Names
Two-word scientific names are used for four reasons.
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.

67. Tools for Identifying Organisms
How are living things classified? 4
Tools for Identifying Organisms
Tools used to identify organisms include field guides and dichotomous (di KAH tuh mus) keys.
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.

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

69. Section Check 4
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.

70. Section Check 4
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.

71. Section Check 4
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.

72. Section Check 4
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

73. Section Check 4
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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