Chap 1 - Text

Note: This is just the text to the chapter.

(top left): Daniel Allan/Image Source; (top right): Ariel Skelley/Getty Images; (bottom left): Luis Alvarez/Digital Vision/Getty Images; (bottom right): Tatomm/iStock/Getty Images

CHAPTER 1

Exploring Life and Science

Diversity in Science

Our planet is home to a staggering diversity of life. Our species, Homo sapiens, is just one of the estimated 8.7 million different species (not counting bacteria) that inhabit the globe. Life may be found every- where, from the deepest ocean trenches to the tops of the highest mountains. Biology is the area of scientific study that focuses on under- standing all aspects of living organisms. Human biology focuses not only on the biology of our species but also its interactions with other species on the planet. This diversity of life is important to humans, be- cause it provides us with food, medicines, and the raw materials needed to manufacture the millions of items that make our way of life possible.

Equally as important as our planet's biodiversity is the diversity of the people who study biology. Scientists rely upon their own experiences to ask questions, develop hypotheses, and design experiments or models to explain natural phenomena. Therefore, in order for the scientific community to ably address the challenges facing human society, from climate change to emerging diseases, we need a diverse population of individuals, with unique experiences and viewpoints, to contribute their ideas and opinions. As we will see throughout this text, there are many ways to study our world, and our diversity is a major strength in developing solutions.

As you read through the chapter, think about the following questions: 1. What are some of the many ways a scientist can study biology? 2. Why would diversity in the scientific community play an important role in addressing how science can address the needs of society?

CHAPTER OUTLINE

#1.1 The Characteristics of Life
1.2 Humans Are Related to Other Animals
1.3 Science as a Process
1.4 Science and the Challenges Facing Society

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Chapter 1 Exploring Life and Science

1.1 The Characteristics of Life

LEARNING OUTCOMES

Upon completion of this section, you should be able to

1. Explain the basic characteristics common to all living organisms.

2. Describe the levels of organization of life.

3. Explain why the study of evolution is important in understanding life.

The science of biology is the study of living organisms and the environments they live in. All living organisms (Fig. 1.1) share several basic characteristics. They (1) are organized, (2) acquire materials and energy, (3) are homeostatic, (4) respond to stimuli, (5) reproduce and have the potential for growth, and (6) have an evolutionary history.

Life Is Organized

Life can be organized in a hierarchy of levels (Fig. 1.2). Note that, at the very base of this organization, atoms join together to form the molecules, which in turn make up a cell. A cell is the smallest

structural and functional unit of an organism. Some organisms, such as bacteria, are single-celled organisms. Humans are multi- cellular, because they are composed of many different types of cells. For example, the structure of nerve cells in the human body allows these cells to conduct nerve impulses.

A tissue is a group of similar cells that perform a particu- lar function. Nervous tissue is composed of millions of nerve cells that transmit signals to all parts of the body. An organ is made up of several types of tissues, and each organ belongs to an organ system. The organs of an organ system work together to accomplish a common purpose. The brain works with the spinal cord to send commands to body parts by way of nerves. Organisms, such as trees and humans, are a collection of organ systems.

The levels of biological organization extend beyond the individual. All the members of one species (a group of inter- breeding organisms) in a particular area belong to a population. A tropical grassland may have a population of zebras, acacia trees, and humans, for example. The interacting populations of the grasslands make up a community. The community of popula- tions interacts with the physical environment to form an ecosystem. Finally, all the Earth's ecosystems collectively make up the biosphere (Fig. 1.2, top).

sunflower

bacteria

9,560x

diverse humans

Giardia

Figure 1.1 All life shares common characteristics.

From the simplest one-celled organisms to complex plants and animals, all life shares several basic characteristics. (student group): FatCamera/E+/Getty Images; (mushrooms): IT Stock/age fotostock; (bacteria): Paul Gunning/Science Photo Library/Getty Images; (gorilla): Mike Price/ Shutterstock; (sunflower): Mediolmages/PunchStock/Getty Images; (Giardia): Dr. Stan Erlandsen/CDC

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Biosphere Regions of the Earth's crust, waters, and atmosphere inhabited by living organisms

Ecosystem

A community plus the physical environment

Community

Interacting populations in

a particular area

Population

Organisms of the same species

in a particular area

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human

tree

Species

A group of similar, interbreeding organisms

Organism

An individual; complex individuals contain organ systems

Organ System

Composed of several organs working together

Organ

Composed of tissues functioning together for a specific task

nervous system

Tissue

A group of cells with a common structure and function

Cell

The structural and functional

unit of all living organisms

Molecule

Union of two or more atoms

of the same or different elements

shoot system

the brain

leaves

nervous tissue

leaf tissue

nerve cell

plant cell

methane

Atom

Smallest unit of an element;

composed of electrons,

protons, and neutrons

Figure 1.2 Levels of biological organization.

oxygen

Life is connected from the atomic level to the biosphere. The cell is the basic unit of life, and it comprises molecules and atoms. The sum of all life on the planet is called the biosphere.

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BIOLOGY IN YOUR LIFE

How many cells are in your body?

The number of cells in a human body varies depending on the size of the person and whether cells have been damaged or lost. However, most estimates suggest there are well over 30 trillion cells in a human body. To put this into perspective, there are only an estimated 3 trillion trees on Earth.

Life Requires Materials and Energy

Humans, like all living organisms, cannot maintain their organization or carry on life's activities without an outside source of materials and energy. Energy is the capacity to do work. Like other animals, humans acquire materials and energy by eating food (Fig. 1.3).

Food provides nutrient molecules, which are used as building blocks or for energy. It takes energy to maintain the organization of the cell and the organism itself. Some nutrient molecules are bro- ken down completely to provide the energy necessary to convert other nutrient molecules into the parts and products of cells. The breakdown of food is a component of our metabolism, or the sum of all the chemical reactions that occur within a cell or organism.

a.

b.

00

Figure 1.3 Humans and other animals must acquire energy. All life, including humans (a) and other animals, such as this eagle (b), must acquire energy to survive. The method by which organisms acquire energy is dependent on the species.

(a): Ariel Skelley/Blend Images/Getty Images; (b): Brian E Kushner/Shutterstock

The ultimate source of energy for the majority of life on Earth is the sun. Plants, algae, and some bacteria are able to harvest the energy of the sun and convert it to chemical energy by a process called photosynthesis. Photosynthesis produces organic mole- cules, such as sugars, that serve as the basis of the food chain for many other organisms, including humans and all other animals.

Living Organisms Maintain an Internal Environment

For the metabolic pathways within a cell to function correctly, the en- vironmental conditions of the cell must be kept within strict operating limits. Many of the metabolic activities of a cell, or organism, function in maintaining homeostasis a constant internal environment.

In humans, many of our organ systems work to maintain homeostasis. For example, human body temperature normally fluc- tuates slightly between 36.5 and 37.5°C (97.7 and 99.5°F) during the day. In general, the lowest temperature usually occurs between 2 A.M. and 4 A.M., and the highest usually occurs between 6 P.M. and 10 P.M. However, activity can cause the body temperature to rise, and inactivity can cause it to decline. The metabolic activities of our cells, tissues, and organs are dependent on maintaining a relatively constant body temperature. Therefore, a number of body systems, including the cardiovascular system and the nervous sys- tem, work together to maintain a constant temperature. The body's ability to maintain a normal temperature is also somewhat depen- dent on the external temperature. Even though we can shiver when we are cold and perspire when we are hot, we will die if the external temperature becomes overly cold or hot.

This text emphasizes how all the systems of the human body help maintain homeostasis. For example, the digestive system takes in nutrients, and the respiratory system exchanges gas with the environment. The cardiovascular system distributes nutrients and oxygen to the cells and picks up their wastes. The metabolic waste products of cells are excreted by the urinary system. The work of the nervous and endocrine systems is critical, because these systems coordinate the functions of the other systems.

Living Organisms Respond

It would be impossible to maintain homeostasis without the body's ability to respond to stimuli, both from the internal and external environments. Response to external stimuli is more apparent to us, because it involves movement, as when we quickly remove a hand from a hot stove. Certain sensory receptors also detect a change in the internal environment, and then the central nervous system brings about an appropriate response. When you are startled by a loud noise, your heartbeat increases, which causes your blood pressure to increase. If blood pressure rises too high, the brain directs blood vessels to dilate, helping restore normal blood pressure.

All life responds to external stimuli, often by moving toward or away from a stimulus, such as the sight of food. Organisms may use a variety of mechanisms to move, but movement in humans and other animals is dependent on their nervous and musculoskeletal systems. The leaves of plants track the passage of the sun during the day; when a houseplant is placed near a window, its stems bend to face the sun. The movement of an animal, whether self-directed

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480x b.

Figure 1.4

Growth and development define life.

a. A small acorn becomes a tree, and (b) following fertilization an embryo becomes a fetus by the process of growth and development. (a) (seedling): bogdan ionescu/Shutterstock; (a) (tree): Frank Krahmer/Photographer's Choice/Getty Images; (b) (sperm/egg): David M. Phillips/Science Source; (b) (fetus): Steve Allen/Brand X Pictures/Getty Images

or in response to a stimulus, constitutes a large part of its behavior. Some behaviors help us acquire food and reproduce.

Living Organisms Reproduce and Develop Reproduction is a fundamental characteristic of life. Cells come into being only from preexisting cells, and all living organisms have parents. When organisms reproduce, they pass on their genetic information to the next generation. Following the fertilization of an egg by a sperm cell, the resulting zygote undergoes a rapid period of growth and development. This is common in most forms of life. Figure 1.4a illustrates that an acorn progresses to a seedling before it becomes an adult oak tree. In humans, growth occurs as the fertilized egg develops into a fetus (Fig. 1.4b). Growth, recognized by an in- crease in size and often in the number of cells, is a part of development. In multicellular organisms, such as humans, the term development is used to indicate all the changes that occur from the time the egg is fertilized until death. Therefore, it includes all the changes that occur during childhood, adolescence, and adulthood. Development also includes the repair that takes place following an injury.

The genetic information of all life is DNA (deoxyribonucleic acid). DNA contains the hereditary information that directs not only the structure of each cell but also its function. The information in DNA is contained within genes, short sequences of hereditary material that specify the instructions for a specific trait. Before reproduction occurs, DNA is replicated so an exact copy of each gene may be passed on to the offspring. When humans reproduce, a sperm carries genes contributed by a male into the egg, which

contains genes contributed by a female. The genes direct both growth and development so that the organism will eventually resemble the parents. Sometimes mutations, minor variations in these genes, can cause an organism to be better suited for its environ- ment. These mutations are the basis of evolutionary change.

Organisms Have an Evolutionary History Evolution is the process by which a population changes over time. The mechanism by which evolution occurs is natural selection (see Section 23.2). When a new variation arises that allows certain members of a population to capture more resources, these members tend to survive and have more offspring than the other, unchanged members. Therefore, each successive generation will include more members with the new variation, which represents an adaptation to the environment. Consider, for example, populations of humans who live at high altitudes, such as the cultures living at elevations of over 4,000 meters (m) (14,000 ft) in the Tibetan Plateau. This envi- ronment is very low in oxygen. As the Science feature "Adapting to Life at High Elevations" investigates, these populations have evolved an adaptation that reduces the amount of hemoglobin, the oxygen-carrying pigment in the blood. As the feature explains, this adaptation makes life at these altitudes possible.

Evolution, which has been going on since the origin of life and will continue as long as life exists, explains both the unity and diversity of life. All organisms share the same characteristics of life because their ancestry can be traced to the first cell or cells. Organ- isms are diverse because they are adapted to different ways of life.

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BIOLOGY TODAY

Science

Adapting to Life at High Elevations

Humans, like all other organisms, have an evolutionary history. This not only means we share common ancestors with other animals, but over time we demonstrate adaptations to changing environmental conditions. One study of populations living in the high-elevation mountains of Tibet (Fig. 1A) demonstrates how the processes of evolution and adaptation influence humans.

Normally, when a person moves to a higher altitude, the body may respond by making more hemoglobin, the component of blood that carries oxygen, which in turn thickens the consistency of the blood. For minor elevation changes, this does not present much of a problem. But for people who live at extreme elevations (some people in the Himalayas can live at elevations of over 13,000 ft, or close to 4,000 m), excess hemoglobin can present a number of health problems, including chronic mountain sickness, a disease that affects people who live at high altitudes for extended periods of time. The problem is that, as the amount of hemoglobin increases, the blood thickens and becomes more viscous. This can cause elevated blood pressure, or hypertension, and an increase in the formation of blood clots, both of which have negative physiological effects.

Figure 1A High-elevation adaptations. Individuals living at high elevations, such as Tibetans, have become adapted to their high-elevation environment.

Michael Freeman/Corbis

Because high hemoglobin levels would be a detriment to people at high elevations, it makes sense that natural selection would favor individuals who produce less hemoglobin at high elevations. Such is the case with the Tibetans in this study. Researchers have identified an allele of a gene that reduces hemoglobin production at high elevations. Comparisons between Tibetans at both high and low elevations strongly suggest that selection has played a role in the prevalence of the high-elevation allele.

The gene is EPSAI, located on chromosome 2 of humans. EPSA1 produces a transcription factor that basically regulates which genes are turned on and off in the body, a process called gene expression. The transcription factor produced by EPSA1 has a num- ber of functions in the body. For example, in addition to controlling the amount of hemoglobin in the blood, this transcription factor also regulates other genes that direct how the body uses oxygen.

When the researchers examined the variations in EPSA1 in the Tibetan population, they discovered that the Tibetan version greatly reduces the production of hemoglobin. Therefore, the Tibetan popula- tion has lower hemoglobin levels than people living at lower altitudes, allowing these individuals to escape the consequences of thick blood.

How long did it take for the original population to adapt to living at higher elevations? Initially, the comparison of variations in these genes between high-elevation and low-elevation Tibetan populations suggested that the event may have occurred over a 3,000-year period. But researchers were skeptical of those data because they suggested a relatively rapid rate of evolutionary change. Additional studies of genetic databases yielded an interest- ing finding the EPSA1 gene in Tibetans was identical to a similar gene found in an ancient group of humans called the Denisovans (see Section 23.5). Scientists now believe that the EPSAI gene en- tered the Tibetan population around 40,000 years ago, either through interbreeding between early Tibetans and Denisovans, or from one of the immediate ancestors of this now-lost group of early humans.

Questions to Consider

1. What other environments do you think could be studied to look for examples of human adaptation?

2. In addition to hemoglobin levels, do you think people at high elevations may exhibit other adaptations?

CHECK YOUR PROGRESS 1.1

1. List the basic characteristics of life.

2. Summarize the levels of biological organization. 3. Explain the relationship between adaptations and evolutionary change.

CONNECTING THE CONCEPTS

Both homeostasis and evolution are central themes in the study of biology. For more examples of homeostasis and evolution, refer to the following discussions:

Section 4.8 explains how body temperature is regulated. Section 11.4 explores the role of the kidneys in fluid and salt homeostasis.

Section 23.3 examines the evolutionary history of humans.

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1.2 Humans Are Related

to Other Animals

LEARNING OUTCOMES

Upon completion of this section, you should be able to

1. Summarize the place of humans in the overall classification of living organisms.

2. Understand that humans have a cultural heritage. 3. Describe the relationship between humans and the biosphere.

Biologists classify all life as belonging to one of three domains. The evolutionary relationships of these domains are presented in Figure 1.5.

Two of these domains, domain Bacteria and domain Archaea, contain prokaryotes, single-celled organisms that lack a nucleus (Fig. 1.6). Organisms in the third domain, Eukarya, all contain cells

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that possess a nucleus. Some of these organisms are single-celled; others are multicellular. Humans are an example of multicelled Eukarya.

Historically, domain Eukarya was divided into one of four kingdoms (Fig. 1.6). However, the development of improved techniques in analyzing the DNA of organisms suggests that not all of the Protistas (the earliest eukaryotes) share the same evolutionary lineage, meaning that the evolution of the eukary- otes has occurred along several paths. A new taxonomic group, called a supergroup, was developed to explain these evolution- ary relationships. There are currently six supergroups for domain Eukarya. Over the past several years, changes have been made to the supergroup classification as new research unveils relationships between these organisms. While these relation- ships are still being studied and analyzed, current thinking places the animals in the same supergroup (the Opisthikonts) as the fungi.

The traditional kingdom level of classification within domain Eukarya is still widely used, and is often placed beneath the

common ancestor (first cells)

domains

kingdoms

common ancestor

EUKARYA

4.0

3.5

3.0

2.5 Billions of Years Ago (BYA)

2.0

1.5

1.0

0.5

0

BACTERIA

ARCHAEA

Protists

Plants

Fungi

Animals

Figure 1.5 The evolutionary relationships of the three domains of life. Living organisms are classified into three domains: Bacteria, Archaea, and Eukarya. The Eukarya are further divided into kingdoms (see Fig. 1.6).

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Domain Archaea

33,200x

Sulfolobus, an archaean

Domain Eukarya; Kingdom Protista

Prokaryotic cells of various shapes Adaptations to

extreme environments • Absorb or

chemosynthesize food Unique chemical characteristics

Domain Bacteria

6,600x

Escherichia coli, a bacterium

• Prokaryotic cells

of various shapes

• Adaptations to

all environments

• Absorb, photosynthesize,

or chemosynthesize food

• Unique chemical

characteristics

160x

Paramecium, a single-celled protozoan

• Algae, protozoans, slime molds, and water molds Complex single cell

(sometimes filaments, colonies, or even multicellular) Absorb, photosynthesize, or ingest food

Domain Eukarya: Kingdom Plantae

Ophrys apifera, bee orchid

• Certain algae, mosses, ferns, conifers, and flowering plants • Multicellular, usually with specialized tissues, containing complex cells • Photosynthesize food

Domain Eukarya: Kingdom Fungi

• Molds, mushrooms, yeasts, and ringworms

• Mostly multicellular filaments with specialized, complex cells • Absorb food

Domain Eukarya: Kingdom Animalia

• Sponges, worms, insects, fishes, frogs, turtles, birds, and mammals • Multicellular with specialized tissues containing complex cells • Ingest food

Amanita muscaria, a mushroom

Figure 1.6 The classification of life.

Buteo jamaicensis, red-tailed hawk

This figure offers some characteristics of organisms in each of the major domains and kingdoms of life. Humans belong to the domain Eukarya and kingdom Animalia.

(archaea): Eye of Science/Science Source; (bacteria): A. Barry Dowsett/Science Source; (paramecium): M.I. Walker/Science Source; (orchids): CreativeNature_nl/iStock/Getty Images; (mushrooms): Ingram Publishing/Getty Images; (hawk): Keneva Photography/Shutterstock

supergroup classification. The four kingdoms are shown in Figure 1.6 and include the following:

Kingdom Protista. Commonly called the protists, this is a very diverse group of eukaryotic organisms, ranging from single-celled forms to a few multicellular organisms. Some protists use photosynthesis to manufacture food, and some must acquire their own food. As we mentioned, the diverse nature of these organisms indicates they have multiple evolu- tionary origins, and thus belong to different supergroups.

• Kingdom Plantae. The plants are multicellular, photosyn- thetic organisms.

Kingdom Fungi. Fungi are the familiar molds and mush- rooms that help decompose dead organisms. Some fungi are parasites of plants and animals.

Kingdom Animalia. Animals are multicellular organisms that must ingest and process their food. They are capable of motion at some point in their life cycle.

Among the animals are the invertebrates, which lack an inter- nal skeletal support structure, called vertebrae. Most animals are invertebrates. Examples include earthworms, insects, and mollusks. Vertebrates are animals that have a nerve cord protected by a verte- bral column, which gives them their name. Fish, reptiles, amphibi- ans, and birds are all examples of vertebrates. Vertebrates with hair or fur and mammary glands are classified as mammals. Humans, raccoons, seals, and meerkats are examples of mammals.

Humans are primate mammals and are most closely related to apes. We are distinguished from apes by our (1) highly developed brains, (2) completely upright stance, (3) creative language, and

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(4) ability to use a wide variety of tools. Humans did not evolve from apes; apes and humans share a common, apelike ancestor. Today's apes are our evolutionary cousins. Our relationship to apes is analogous to you and your first cousin being descended from your grandparents. We could not have evolved directly from our cousins, because we are contemporaries living on Earth at the same time.

Humans Have a Cultural Heritage

Humans have a cultural heritage in addition to a biological heri- tage. Culture encompasses human activities and products passed on from one generation to the next outside of direct biological inheritance. Among animals, only humans have a language that al- lows us to communicate information and experiences symbolically. We are born without knowledge of an accepted way to behave, but we gradually acquire this knowledge by adult instruction and the imitation of role models. Members of the previous generation pass on their beliefs, values, and skills to the next generation. Many of the skills involve tool use, which can vary from how to hunt in the wild to how to use a computer. Human skills have also produced a rich heritage in the arts and sciences. However, a society highly dependent on science and technology has its drawbacks as well. Unfortunately, this cultural development may mislead us into be- lieving that humans are somehow not part of the natural world surrounding us.

Humans Are Members of the Biosphere

All life on Earth is part of the biosphere, the living network that spans the surface of the Earth into the atmosphere and down into the soil and seas. Although humans can raise animals and crops for food, we depend on the environment for many services. Without microorganisms that decompose, the waste we create would soon cover the Earth's surface. Some species of bacteria help us by cleaning up pollutants like heavy metals and pesticides.

Freshwater ecosystems, such as rivers and lakes, provide fish to eat, water to drink, and water to irrigate crops. Many of our crops and prescription drugs were originally derived from plants that grew naturally in an ecosystem. Some human populations around the globe still depend on wild animals as a food source. The water-holding capacity of forests prevents flooding, and the ability of forests and other ecosystems to retain soil prevents soil erosion. For many people, these forests provide a place for recreational activities like hiking and camping.

BIOLOGY IN YOUR LIFE

How many humans are there?

In 2021, it was estimated there were over 7.9 billion humans on the planet. Each human needs food, shelter, clean water and air, and materials to maintain a healthy lifestyle. Our species adds an additional 83 million people per year-that is like adding the population of ten New York Cities annually! This makes human population growth one of the greatest threats to the biosphere.

CHECK YOUR PROGRESS 1.2

1. Define the term biosphere.

2. Define culture.

3. Explain why humans belong to the domain Eukarya and kingdom Animalia.

CONNECTING

THE

CONCEPTS

To learn more about the preceding material, refer to the following discussions:

Chapter 23 examines recent developments in the study of human evolution.

Chapter 24 provides a more detailed look at ecosystems. Chapter 25 explores how humans interact with the biosphere.

1.3 Science as a Process

LEARNING OUTCOMES

Upon completion of this section, you should be able to

1. Describe the general process of the scientific method. 2. Distinguish between a control group and an experimental group in a scientific test.

2. Recognize the importance of scientific journals in the reporting of scientific information.

3. Recognize the importance of statistical analysis to the study of science.

Science is a way of knowing about the natural world. When scien- tists study the natural world, they aim to be objective, rather than subjective. Objective observations are supported by factual informa- tion, whereas subjective observations involve personal judgment. For example, the fat content of a particular food would be an objective observation of a nutritional study. Reporting about the good or bad taste of the food would be a subjective observation. It is difficult to make objective observations and conclusions, because we are often influenced by our prejudices. Scientists must keep in mind that scientific conclusions can change because of new findings. New findings are often made because of recent advances in techniques or equipment.

Religion, aesthetics, ethics, and science are all ways in which humans seek order in the natural world. The nature of scientific inquiry differs from these other ways of knowing and learning, because the scientific process employs the scientific method, a standard series of steps used in gaining new knowledge that is widely accepted among scientists. The scientific method (Fig. 1.7) acts as a guideline for scientific studies.

The approach of individual scientists to their work is as varied as the scientists. However, much of the scientific process cess is de- scriptive. For example, an observation of a new disease may lead a scientist to describe all the aspects of the disease, such as the envi- ronment, the age of onset, and the characteristics of the disease. Some areas of biology, such as the study of biodiversity in the

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Observation

Potential hypotheses

Hypothesis 1 Hypothesis 2 Hypothesis 3

Prediction

Experiment

Reject hypothesis 1

hypothesis 2

Remaining possible hypotheses

Hypothesis 2 Hypothesis 3

Reject

Prediction

Experiment

Last remaining possible hypothesis

Hypothesis 3

Modify hypothesis

Experiment 1

Predictions

Experiment 2 Experiment 3 Experiment 4

Predictions confirmed

Conclusion

ecological sciences (see Section 1.4), lend themselves more to this descriptive approach. Regardless of their area of study, most scien- tists spend a considerable amount of time performing a descriptive analysis of their observation before proceeding into the steps of the scientific method. Scientists often modify or adapt the process to suit their particular field of study, but for the sake of discussion, it is useful to think of the scientific method as consisting of certain logical steps.

Start with an Observation

Scientists believe that nature is orderly and measurable that natu- ral laws, such as the law of gravity, do not change with time-and that a natural event, or phenomenon, can be understood more fully through observation-a formal way of watching the natural world.

Observations may be made with the senses, such as sight and smell, or with instruments; for example, a microscope enables us to see objects that could never be seen by the naked eye. Scientists may expand their understanding even further by taking advantage of the knowledge and experiences of other scientists. For instance, they may look up past studies on the Internet or at the library, or they may write or speak to others who are researching similar topics.

Develop a Hypothesis

After making observations and gathering knowledge about a phenomenon, a scientist uses inductive reasoning. Inductive reasoning occurs whenever a person uses creative thinking to combine isolated facts into a cohesive whole. Chance alone can help a scientist arrive at an idea. The most famous case pertains to the antibiotic penicillin, which was discovered in 1928. While

Figure 1.7 The scientific method. On the basis of new and/or previous observations, a scientist formulates a hypothesis. The hypothesis is used to develop predictions to be tested by further experiments and/or observations, and new data either support or do not support the hypothesis. Following an experiment, a scientist often chooses to retest the same hypothesis or to test a related hypothesis. Conclusions from many different but related experiments may lead to the development of a scientific theory. For example, studies pertaining to development, anatomy, and fossil remains all support the theory of evolution.

examining a petri dish of bacteria that had accidentally become contaminated with the mold Penicillium, Alexander Fleming ob- served an area around the mold that was free of bacteria. Fleming had long been interested in finding cures for human diseases caused by bacteria, and he was very knowledgeable about antibac- terial substances. So when Fleming saw the dramatic effect of Penicillium mold on bacteria, he reasoned that the mold might be producing an antibacterial substance.

We call such a possible explanation for a natural event a hypothesis. A hypothesis is based on existing knowledge, so it is much more informed than a mere guess. Fleming's hypothesis was supported by further study, but sometimes a hypothesis is not sup- ported and must be either modified and subjected to additional study or rejected. When thinking about how to test the hypothesis, the scientist may make a prediction, or an expected outcome, based on knowledge of the factors involved in the observation.

All of a scientist's past experiences, no matter what they might be, may influence the formation of a hypothesis. But a scientist considers only hypotheses that can be tested by experiments or further observations. Moral and religious beliefs, although very important to our lives, differ among cultures and through time and are not always testable.

Test the Hypothesis

Scientists often perform an experiment, which is a series of proce- dures, to test a hypothesis. To determine how to test a hypothesis, a scientist uses deductive reasoning. Deductive reasoning involves "if... then" logic.

The manner in which a scientist intends to conduct an experi- ment is called the experimental design. A good experimental design

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64x

Drosophila melanogaster

Caenorhabditis elegans

Arabidopsis thaliana

Mus musculus

Figure 1.8 Model organisms used in scientific studies. Drosophila melanogaster is used as a model organism in the study of genetics. Mus musculus is used in the study of medicine. Caenorhabditis elegans is used by developmental biologists, and Arabidopsis thaliana is used by botanists to understand plant genetics. (Drosophila): janeff/iStockphoto/Getty Images; (C. elegans): Sinclair Stammers/ Science Source; (Arabidopsis): Wildlife GmbH/Alamy Stock Photo; (M. musculus): Redmond Durrell/Alamy Stock Photo

ensures that scientists are examining the contribution of a specific variable, called the experimental variable, to the observation. The result is termed the responding variable, or dependent variable, because it is due to the experimental variable.

To ensure the results will be meaningful, an experiment con- tains both test groups and a control group. A test group is exposed to the experimental variable, but the control group is not. If the control group and test groups show the same results, the experi- menter knows that the hypothesis predicting a difference between them is not supported.

y-axis

Scientists often use model organisms and model systems to test a hypothesis. Some common model organ- isms are shown in Figure 1.8. Model organisms are chosen because they allow the researcher to control aspects of the experiment, such as age and genetic background. Cell biologists may use mice for modeling the effects of a new drug. Like model organisms, model systems allow the scientist to con- trol specific variables and environmental conditions in a way that may not be possible in the natural environment. For example, ecologists may use computer programs to model how human activities will affect the climate of a specific ecosystem. While models provide useful information, they do not always answer the original question completely. For example, medicine that is effec- tive in mice ideally should be tested in humans, and ecological experiments conducted using computer simulations need to be verified by actual field experiments.

Chapter 1 Exploring Life and Science 11

Collect and Analyze the Data

The data, or results, from scientific experiments may be pre- sented in a variety of formats, including tables and graphs. A graph shows the relationship between two quantities. In many graphs, the experimental variable is plotted on the x-axis (hori- zontal), and the result is plotted along the y-axis (vertical). Graphs are useful tools to summarize data in a clear and simpli- fied manner. For example, the line graph in Figure 1.9 shows the variation in the concentration of blood cholesterol over a 4-week study. The bar above and below each data point represents the variation, or standard error, in the results. The title and labels can assist you in reading a graph; therefore, when looking at a graph, first check the two axes to determine what the graph per- tains to. By looking at this graph, we know the blood cholesterol levels were highest during week 2, and we can see to what degree the values varied over the course of the study.

Statistical Data

Most scientists who publish research articles use statistics to help them evaluate their experimental data. In statistics, the standard error, or standard deviation, tells us how uncertain a particular value is. Suppose you predict how many hurricanes Florida will have next year by calculating the average number during the past 10 years. If the number of hurricanes per year varies widely, your standard error will be larger than if the number per year is usually about the same. In other words, the standard error tells you how far off the average could be. If the average number of hurricanes is four and the standard error is $\pm 2$, then your prediction of four hurricanes is between two and six hurricanes. In Figure 1.9, the standard error is represented by the bars above and below each data point. This provides a visual indication of the statistical analysis of the data.

Blood Cholesterol (mg/dl)

Variation in Blood Cholesterol Levels

225

200

Data

175

standard error

150

T

Week 1

Week 2

Week 3

Week 4

x-axis

Figure 1.9 The presentation of scientific data. This line graph shows the variation in the concentration of blood cholesterol over a 4-week study. The bars above and below the data points represent the variation, or standard error, in the results.

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Chapter 1 Exploring Life and Science

Statistical Significance

When scientists conduct an experiment, there is always the possibil- ity that the results are due to chance or to some factor other than the experimental variable. Investigators take into account several factors when they calculate the probability value (p) that their results were due to chance alone. If the probability value is low, researchers describe the results as statistically significant. A probability value of less than 5% (usually written as $p<0.05)$ is acceptable; even so, keep in mind that the lower the p value, the less likely it is that the results are due to chance. Therefore, the lower the p value, the greater the confidence the investigators and you can have in the results. Depending on the type of study, most scientists like to have a p value of $<0.05$ but p values of < 0.001 are common in many studies.

Scientific Publications

Scientific studies are customarily published in scientific journals, such as Science or Nature, so that all aspects of a study are avail- able to the scientific community. Before information is published in scientific journals, it is typically reviewed by experts, who ensure that the research is credible, accurate, unbiased, and well executed. Another scientist should be able to read about an experi- ment in a scientific journal, repeat the experiment in a different location, and get the same (or very similar) results. Some articles are rejected for publication by reviewers when they believe there is something questionable about the design of an experiment or the manner in which it was conducted. This process of rejection is important in science because it causes researchers to critically review their hypotheses, predictions, and experimental designs, so that their next attempt will more adequately address their hypoth- esis. Often, it takes several rounds of revision before research is accepted for publication in a scientific journal.

People should be especially careful about scientific information available on the Internet, which is not well regulated. Reliable, cred- ible scientific information can often be found at websites with URLs containing .edu (for educational institution), .gov (for government sites such as the National Institutes of Health or the Centers for Dis- ease Control and Prevention), and .org (for nonprofit organizations, such as the American Lung Association or the National Multiple Sclerosis Society). Unfortunately, quite a bit of scientific informa- tion on the Internet is intended to entice people into purchasing some sort of product for weight loss, prevention of hair loss, or simi- lar maladies. These websites usually have URLs ending with .com or .net. It pays to question and verify the information from these websites with another source (a primary source, if possible).

Develop a Conclusion

Scientists must analyze the data in order to reach a conclusion about whether a hypothesis is supported or not. Because science progresses, the conclusion of one experiment can lead to the hy- pothesis for another experiment (see Fig. 1.9). In other words, results that do not support one hypothesis can often help a scientist formulate another hypothesis to be tested. Scientists report their findings in scientific journals, so that their methodology and data are available to other scientists.

Scientific Theory

The ultimate goal of science is to understand the natural world in terms of scientific theories, which are accepted explanations for how the world works. Some of the basic theories of biology are the cell theory, which says that all organisms are composed of cells; the gene theory, which says that inherited information in a gene contributes to the form, function, and behavior of organisms; and the theory of evolution, which says that all organisms have a common ancestor and that each organism is adapted to a particu- lar way of life.

The theory of evolution is considered the unifying concept of biology, because it pertains to many different aspects of or- ganisms. For example, the theory of evolution enables scientists to understand the history of life, the variety of organisms, and the anatomy, physiology, and development of organisms. The theory of evolution has been a very fruitful scientific theory, meaning it has helped scientists generate new testable hypotheses. Because this theory has been supported by so many observations and experiments for over 100 years, some biologists refer to the theory of evolution as the principle of evolution, a term sometimes used for theories that are generally accepted by an overwhelming number of scientists. Others prefer the term law instead of principle.

An Example of a Controlled Study

As presented in the Science feature "Discovering the Cause of Ulcers," we now know that most stomach and intestinal ulcers (open sores) are caused by the bacterium Helicobacter pylori.

Experimental Design

Let's say investigators want to determine which of two antibiotics is best for the treatment of an ulcer. When clinicians do an experi- ment, they try to vary just the experimental variables in this case, the medications being tested. Each antibiotic is administered to an independent test group. The control group is not given an antibi- otic. If by chance the control group shows the same results as one of the test groups, the investigators may conclude that the anti- biotic in that test group is ineffective, because it does not show a result that is significantly different from that of the control group. The study depicted in Figure 1.10a shows how investigators may study this hypothesis:

Hypothesis: Newly discovered antibiotic B is a better treatment for ulcers than antibiotic A, which is in current use.

In any experiment, it is important to reduce the number of possible variables (differences). In this experiment, those variables may include factors such as differences in the subjects' sex, weight, and previous illnesses. Therefore, the investigators randomly di- vide a large group of volunteers equally into experimental groups. The hope is that any any differences will be distributed evenly among the three groups. The larger the number of volunteers (the sample size), the greater the chance of reducing the influence of external variables. This is why many medical studies involve thousands of individuals.

ISTUDY

State Hypothesis:

Antibiotic B is a better treatment for ulcers than antibiotic A.

Perform Experiment: Groups were treated the same except as noted.

Control group:

received

placebo

Test group 1: received

antibiotic A

Analyze the Data:

Test group 2: received antibiotic B

Graph the data to analyze for

statistical differences.

a. Experimental design

100-

80-

Effectiveness of Treatment

Chapter 1 Exploring Life and Science 13

After the investigators have determined that all volunteers do have ulcers, they will want the subjects to think they are all receiv- ing the same treatment. This is an additional way to protect the results from any influence other than the medication. To achieve this end, the subjects in the control group can receive a placebo, a treatment that appears to be the same as that administered to the other two groups but that actually contains no medication. In this study, the use of a placebo would help ensure that all subjects are equally dedicated to the study.

The Results and Conclusion

After 2 weeks of administering the same amount of medication (or placebo) in the same way, researchers examine the stomach and intestinal linings of each subject to determine if ulcers are still present. Endoscopy is one way to examine a patient for the pres- ence of ulcers. This procedure, which is performed under sedation, involves inserting an endoscope-a small, flexible tube with a tiny camera on the end-down the throat and into the stomach and the upper part of the intestine. Then, the doctor can see the lining of these organs and can check for ulcers. Tests performed during an endoscopy can also determine if Helicobacter pylori is present.

Because endoscopy is somewhat subjective, it is probably best if the examiner is not aware of which group the subject is in; oth- erwise, examiner prejudice may influence the examination. When neither the patient nor the technician is aware of the specific treat- ment, it is called a double-blind study.

In this study, the investigators may decide to determine the effectiveness of the medication by the percentage of people who no longer have ulcers. So, if 20 people out of 100 still have ulcers, the medication is 80% effective. The difference in effectiveness is easily read in the graph portion of Figure 1.10b.

Conclusion: On the basis of their data, the investigators conclude that their hypothesis has been supported.

% Treated

60

40-

80

60

20-

0

10 Control

Group

Test Group 1

b. Experimental data

Test Group 2

Figure 1.10 Example of a controlled study.

a. The experimental design of the controlled study. b. The experimental data displayed as a graph showing that medication B was a more effective treatment than medication A for the treatment of ulcers. (students, all photos): René Mansi/E+/Getty Images

CHECK YOUR PROGRESS 1.3

1. Describe each step of the scientific method.

2. Explain why a controlled study is an important part of the experimental design.

3. List a few pros and cons of using a scientific journal versus other sources of information.

4. Summarize how the use of graphs and statistics aids in

data analysis.

In this experiment, the researchers divide the individuals into three groups:

Control group: Subjects with ulcers are not treated with either antibiotic.

Test group 1: Subjects with ulcers are treated with antibiotic A. Test group 2: Subjects with ulcers are treated with antibiotic B.

CONNECTING

THE

CONCEPTS

For more information on the topics presented in this section, refer to the following discussions:

Section 8.4 discusses how resistance to antibiotics occurs. Section 9.3 provides more information on ulcers.

Figure 14.4 shows the relationship between an action potential and voltage across a plasma membrane.

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Chapter 1 Exploring Life and Science

BIOLOGY TODAY

Science

Discovering the Cause of Ulcers

In 1974, Barry James Marshall (Fig. 1B) was a young resident physician at Queen Elizabeth II Medical Center in Perth, Australia. There he saw many patients who had bleeding stomach ulcers. A pathologist at the hospital, Dr. J. Robin Warren, told him about finding a particular bacterium, now called Helicobacter pylori, near the site of peptic ulcers. Marshall compiled data showing a possible correlation between the presence of H. pylori and the occurrence of both gastritis (inflammation of the stomach) and stomach ulcers. On the basis of these data, Marshall formulated a hypothesis: H. pylori is the cause of gastritis and ulcers.

Marshall decided to make use of Koch's postulates, the stan- dard criteria that must be fulfilled to show that a pathogen (bacte- rium or virus) causes a disease:

The suspected pathogen (virus or bacterium) must be present in every case of the disease.

The pathogen must be isolated from the host and grown in a lab dish.

The disease must be reproduced when a pure culture of the pathogen is inoculated into a healthy susceptible host. The same pathogen must be recovered again from the experi- mentally infected host.

By 1983, Marshall had fulfilled the first and second of Koch's cri- teria. He was able to isolate H. pylori from patients with ulcers and grow it in the laboratory. Despite Marshall's presentation of these findings to the scientific community, most physicians continued to believe that stomach acidity and stress were the causes of stomach ulcers. In those days, patients were usually advised to make drastic changes in their lifestyle to cure their ulcers. Many scientists believed that no bacterium would be able to survive the normal acidity of the stomach.

Marshall had a problem in fulfilling the third and fourth of Koch's criteria. He had been unable to infect guinea pigs and rats with the bacteria, because the bacteria did not flourish in the intes- tinal tracts of those animals. Marshall was not able to use human subjects because of ethical reasons. Marshall was so determined to support his hypothesis that in 1985 he decided to perform the ex- periment on himself! To the disbelief of those in the lab that day, he and another volunteer swallowed a foul-smelling, foul-tasting solution of H. pylori. Within the week, they felt lousy and were vomiting up their stomach contents. Examination by endoscopy showed that their stomachs were now inflamed, and biopsies of the stomach lining contained the suspected bacterium (Fig. 1B). Their

16,000x Helicobacter pylori

Figure 1B The cause of stomach ulcers. Research by Dr. Barry Marshall showed that stomach ulcers (left) are often caused by Helicobacter pylori (right).

(ulcer): Dr. E. Walker/Science Source; (H. pylori): Heather Davies/Science Photo Library/Science Source

symptoms abated without need for medication, and they never developed an ulcer. Marshall challenged the scientific community to refute his hypothesis. Many tried, but ultimately the investigators supported his findings.

In science, many experiments, often involving a considerable number of subjects, are required before a conclusion can be reached. By the early 1990s, at least three independent studies in- volving hundreds of patients had been published showing that anti- biotic therapy can eliminate H. pylori from the intestinal tract and cure patients of ulcers wherever they occurred in the tract.

Dr. Marshall and Dr. Warren received a Nobel Prize in Physiology or Medicine in 2005. The Nobel committee reportedly thanked Marshall and Warren for their "pioneering discovery," stating that peptic ulcer disease now could be cured with antibiot- ics and acid-secretion inhibitors rather than becoming a "chronic, frequently disabling condition."

Questions to Consider

1. Explain how Marshall's approach was similar to, and different from, the scientific method shown in Figure 1.7.

2. How could Marshall have done this experiment if he had an animal model to work with?

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1.4 Science and the Challenges Facing Society

LEARNING OUTCOMES

Upon completion of this section, you should be able to

1. Distinguish between science and technology.

2. Summarize some of the major challenges facing science.

As we have learned in this chapter, science is a systematic way of acquiring knowledge about the natural world. Science is a slightly different endeavor than technology. Technology is the application of scientific knowledge to the interests of humans. Scientific investigations are the basis for the majority of our technological advances. As is often the case, a new technology, such as your cell phone or a new drug, is based on years of scientific investigations. In this section, we are going to explore some of the challenges facing science, technology, and society.

Climate Change

The overwhelming consensus within the scientific community is that the single greatest challenge facing science and society, and the greatest threat to both humans and the environment, is climate change. The term climate change refers to changes in the normal cycles of the Earth's climate that may be attributed to human activity. Climate change is primarily due to an imbal- ance in the chemical cycling of the element carbon. Normally, carbon is cycled within an ecosystem (see Section 24.3). How- ever, due to human activities, more carbon dioxide is being released into the atmosphere than is being removed. In 1850, atmospheric $C{O}_2$ was at about 280 parts per million (ppm). Today, it is over 415 ppm (Fig. 1.11). This increase is largely due to the burning of fossil fuels and the destruction of forests to make way for farmland and pastures. The amount of carbon dioxide released into the atmosphere today is about twice the

CO2 (parts per million)

415

410

405

400

395

390

385

380

2006 2008 2010 2012

Figure 1.11

Year

Chapter 1 Exploring Life and Science 15

amount that remains in the atmosphere. It is believed that most of this dissolves in the oceans, which are increasing in acidity. The increased amount of carbon dioxide (and other gases) in the atmosphere is causing a rise in temperature called global warming. These gases allow the sun's rays to pass through them, but they then absorb and radiate heat back to Earth, a phenomenon called the greenhouse effect.

There is a consensus among scientists from around the globe that climate change and global warming are causing significant changes in many of the Earth's ecosystems and represent one of the greatest challenges of our time. Throughout this text, we will return to see how climate change is impacting humans, from the loss of biodiversity to increases in the rates of certain types of human disease. We will examine climate change in more detail in Chapters 24 and 25.

Biodiversity and Habitat Loss

The term biodiversity represents the total number and relative abundance of species, the variability of their genes, and the dif- ferent ecosystems in which they live. The biodiversity of our planet has been estimated to be around 8.7 million species (not counting bacteria), and so far, approximately 2.3 million have been identified and named. Extinction is the death of a species or larger classification category. It is estimated that presently we are losing hundreds of species every year due to human activities and that as much as 27% of all identified species, including most primates, birds, and amphibians, may be in danger of extinction before the end of the century. In many cases, these extinctions are accelerated by a combination of habitat loss and climate change (Fig. 1.12). Many biologists are alarmed about the present rate of extinction and hypothesize it may eventually rival the rates of the five mass extinctions that occurred during our planet's history. The last mass extinction, about 65 million years ago, caused many plant and animal species, including the dinosaurs, to become extinct.

2014 2016 2018 2020

Increases in atmospheric carbon dioxide concentrations. The global average carbon dioxide $(C{O}_2)$ concentration now exceeds 415 ppm and is the major contributing factor to climate change and global warming.

NOAA, "Global Climate Change: Facts." http://climate.nasa.gov/vital-signs/carbon-dioxide/.

The two most biologically diverse ecosystems- tropical rain forests and coral reefs are home to many organisms. These ecosystems are also threat- ened by human activities. The canopy of the tropical rain forest alone supports a variety of organisms, in- cluding orchids, insects, and monkeys. Coral reefs, which are found just offshore of the continents and islands near the equator, are built up from calcium carbonate skeletons of sea animals called corals. Reefs provide a habitat for many animals, including jellyfish, sponges, snails, crabs, lobsters, sea turtles, moray eels, and some of the world's most colorful fishes. Like tropical rain forests, coral reefs are se- verely threatened as the human population increases in size. Some reefs are 50 million years old, yet in just a few decades, human activities have destroyed an es- timated 25% of all coral reefs and seriously degraded another 30%. At this rate, nearly three-quarters could be destroyed within 40 years. Similar statistics are available for tropical rain forests.

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Chapter 1 Exploring Life and Science

Figure 1.12 Loss of Biodiversity.

Of the 111 known species of lemurs, all of which are found on the island of Madagascar, 105 are classified as endangered or threatened by extinction.

Gudkov Andrey/Shutterstock

The destruction of healthy ecosystems has many unintended effects. For example, we depend on them for food, medicines, and various raw materials. Draining of the natural wetlands of the Mississippi and Ohio Rivers and the construction of levees have worsened flooding problems, making once-fertile farmland unde- sirable. The destruction of South American rain forests has killed many species that may have yielded the next miracle drug and has decreased the availability of many types of lumber. We are only now beginning to realize that we depend on ecosystems even more for the services they provide. Just as chemical cycling occurs within a single ecosystem, so all ecosystems keep chemicals cycling throughout the biosphere. The workings of ecosystems ensure that the environmental conditions of the biosphere are suit- able for the continued existence of humans. In fact, several studies show that ecosystems cannot function properly unless they remain biologically diverse. We will explore the concept of biodiversity in greater detail in later chapters of this text.

Emerging and Reemerging Diseases

Over the past decade, avian influenza (H5N1 and H7N9), swine flu (H1N1), severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS) have been in the news. In 2020, a global pandemic called COVID-19 was caused by a new form of SARS virus named SARS-CoV-2. These are called emerging diseases because they are relatively new to humans.

Where do emerging diseases come from? Some of them may result from new and/or increased exposure to animals or insect populations that act as vectors for disease. Changes in human be- havior and use of technology can also result in new diseases. For example, Legionnaires' disease emerged in 1976 due to bacterial contamination of a large air-conditioning system in a hotel. The bacteria thrived in the cooling tower used as the water source for the air-conditioning system. SARS is thought to have arisen in Guandong, China, due to the consumption of civets, a type of ex- otic cat considered a delicacy. The civets were possibly infected by exposure to horseshoe bats sold in open markets. While the source of SARS-CoV-2 is still being investigated, it is also thought to have resulted from human contact with, or consumption of, horseshoe bats.

In addition, globalization results in the transport all over the world of diseases previously restricted to isolated communities. The first SARS-CoV-2 cases were reported in Wuhan, China, in November 2019. By the end of March 2020, SARS-CoV-2, and the respiratory illness it caused, COVID-19, had spread globally and was found in every country and continent, except Antarctica, on the globe. As of this writing in 2021, COVID-19 had infected over 210 million people worldwide and resulted in over 4.4 million deaths.

Some pathogens mutate and change hosts, jumping from birds to humans, for example. Before 1997, avian flu was thought to affect only birds. A mutated strain jumped to humans in the 1997 outbreak. To control that epidemic, officials killed 1.5 million chickens to remove the source of the virus. New forms of avian influenza (bird flu) are being discovered every few years. As mentioned, the SARS-CoV-2 virus is believed to have jumped to humans from horseshoe bats, but other species, such as pangolins, may have been involved.

Reemerging diseases are also a concern. Unlike an emerg- ing disease, a reemerging disease has been known to cause dis- ease in humans for some time, but generally has not been considered a health risk due to a relatively low level of inci- dence in human populations. Even so, reemerging diseases can cause problems. One example is the Ebola outbreak in West Africa of 2014-2015. Ebola outbreaks have been known since 1976, but have generally affected only small groups of humans. The 2014-2015 outbreak was a much larger event. Although the exact numbers may never be known, it is estimated that over 28,000 people were infected, with over 11,000 fatalities. Smaller outbreaks occurred in Africa in 2016 and 2018. These outbreaks have the potential to disrupt the societies of several West African nations.

As we are learning from COVID-19, both emerging and reemerging diseases have the potential to cause global health prob- lems for humans, as well as disrupt economies and the structure of human societies. Scientists investigate not only the causes of these diseases (for example, the viruses) but also their effects on our bodies and the mechanisms by which they are transmitted. We will take a closer look at pathogens, such as viruses, in Section 8.1, and emerging diseases in Section 8.2.

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Chapter 1 Exploring Life and Science 17

CONNECTING

THE

CONCEPTS

CHECK YOUR PROGRESS 1.4

1. Explain how a new technology differs from a scientific discovery.

2. Explain why the conservation of biodiversity is important to human society.

3. Summarize how emerging diseases and climate change have the potential to influence the entire human population.

For more information on these challenges facing human society, refer to the following discussions:

Section 8.3 provides additional information on emerging and reemerging diseases.

Section 24.3 examines the impact of climate change and global warming on ecosystems.

Section 25.3 explores the importance of preserving biodiversity.

CONCLUSION

In the beginning of this chapter, we introduced the importance of diversity to science. Throughout this chapter, you have explored some of the basic characteristics of life as we currently under- stand it, the processes by which science is performed, and the

importance of science in addressing the needs of society. The diversity of backgrounds, opinions, and ideas that comes from a di- verse scientific community will play an important role in making the study of biology relevant, and important, to all of human society.

SUMMARIZE

1.1 The Characteristics of Life

Biology is the study of life. All living organisms share common characteristics:

They have levels of organization-atoms, molecules, cells, tissues, organs, organ systems, organisms, species, populations, community, ecosystem, and biosphere.

They acquire materials and energy from the environment. Metabolism is the sum of the reactions involved in these processes. Photosynthesis, which occurs in organisms such as plants, is responsible for producing the organic molecules that serve as food for most organisms.

They reproduce and experience growth, and in many cases development. The instructions for these processes are contained within the DNA (deoxyribonucleic acid) and are organized as genes. Mutations cause variations of those instructions.

They maintain an internal environment, called homeostasis, that operates within a narrow range of environmental factors. They respond to stimuli.

As species, they are influenced by natural selection as the process that results in evolution and adaptation to their environment over time.

1.2 Humans Are Related to Other Animals

The classification of living organisms mirrors their evolutionary relation- ships. Humans are animals that belong to the animal kingdom of the domain Eukarya. Other kingdoms include the plants, protists, and fungi. A new classification, called a supergroup, is being developed to describe evolutionary relationships based on DNA analyses.

In addition to their evolutionary history, humans have a cultural heritage in which language, tool use, values, and information are passed on from one generation to the next.

Like all life, humans are members of the biosphere. Humans depend on the biosphere for its many services, such as absorption of pollutants, sources of water and food, prevention of soil erosion, and natural beauty.

1.3 Science as a Process

When studying the natural world, scientists use a process called the scientific method.

Observations, along with previous data, are used to formulate a hypothesis. Inductive reasoning allows a scientist to combine facts into a hypothesis.

New observations and/or experiments are carried out in order to test the hypothesis. Through deductive reasoning, scientists can develop a prediction of what may occur as a result of the experiment. A good experimental design includes an experimental variable and a control group. Scientists may use models and model organisms in their experimental design.

The data from the experimental and observational results are analyzed, often using statistical methods. The results are often presented in tables or graphs for ease of interpretation.

A conclusion is made as to whether the results support the hypothesis or do not support the hypothesis.

The results may be submitted to a scientific publication for review by the scientific community.

Over time, multiple conclusions in a particular area may allow scientists to arrive at a theory (or principle or law), such as the cell theory or the theory of evolution. The theory of evolution is a unifying concept of biology.

1.4 Science and the Challenges Facing Society

While science investigates the principles of the natural world, technology applies this knowledge to the needs of society. Some challenges that scientists are investigating include:

The impact of climate change and global warming. The loss of biodiversity and habitats such as coral reefs and rain forests. This often results in the extinction of species. Emerging diseases, such as avian influenza and SARS, and reemerging diseases, such as Ebola.

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18 Chapter 1 Exploring Life and Science

ENGAGE

BioNOW

Want to know how this science is relevant to your life? Check out the BioNOW video below:

Characteristics of Life

McGraw Hill

Which step of the scientific method was represented in this video? How was it accomplished and which steps would follow?

THINKING CRITICALLY

1. Explain how climate change and loss of biodiversity may produce health threats for humans. Give an example of how scientists have already documented instances where this is occurring.

2. You are a scientist working at a pharmaceutical company and have developed a new cancer medication that has the potential for use in humans. Outline a series of experiments, including the use of a model, to test whether the cancer medication works.

3. Scientists have been exploring the possibility of life on other planets and moons of our solar system. If life is found to exist outside of Earth, will that change our definition of the basic characteristics of life? Will it change our definition of a biosphere?

MAKING IT RELEVANT

1. Why is it important for the scientific community to be diverse to address the needs facing society due to climate change?

2. How might a diverse scientific community be able to better address the loss of biodiversity at a local level?

3. Emerging diseases often occur in rural areas of the globe, where scientific education is minimal. What are some ways a diverse and global community of scientists can help reduce the risk of these diseases becoming a problem?

Find answers to all of the chapter questions at connect.mheducation.com