Exploring Life and Science Textbook PDF 2024

C H A P T E R 1...

C H A P T E R 1 Exploring Life and Science (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 Diversity in Science CHAPTER OUTLINE 1.1 The Characteristics of Life Our planet is home to a staggering diversity of life. Our species, 1.2 Humans Are Related to Other Animals 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- 1.3 Science as a Process where, from the deepest ocean trenches to the tops of the highest 1.4 Science and the Challenges Facing mountains. Biology is the area of scientific study that focuses on under- Society 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 experi- ences 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? ISTUDY  2 Chapter 1 Exploring Life and Science structural and functional unit of an organism. Some organisms, 1.1 The Characteristics of Life such as bacteria, are single-celled organisms. Humans are multi- cellular, because they are composed of many different types of LE AR N I N G OUTCO M E S cells. For example, the structure of nerve cells in the human body Upon completion of this section, you should be able to allows these cells to conduct nerve impulses. 1. Explain the basic characteristics common to all living A tissue is a group of similar cells that perform a particu- organisms. lar function. Nervous tissue is composed of millions of nerve 2. Describe the levels of organization of life. cells that transmit signals to all parts of the body. An organ is 3. Explain why the study of evolution is important in made up of several types of tissues, and each organ belongs to understanding life. an organ system. The organs of an organ system work together to accomplish a common purpose. The brain works with the The science of biology is the study of living organisms and the spinal cord to send commands to body parts by way of nerves. environments they live in. All living organisms (Fig. 1.1) share Organisms, such as trees and humans, are a collection of several basic characteristics. They (1) are organized, (2) acquire organ systems. materials and energy, (3) are homeostatic, (4) respond to stimuli, The levels of biological organization extend beyond the (5) reproduce and have the potential for growth, and (6) have an individual. All the members of one species (a group of inter- evolutionary history. 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 Life Is Organized the grasslands make up a community. The community of popula- Life can be organized in a hierarchy of levels (Fig. 1.2). Note that, tions interacts with the physical environment to form an ecosystem. at the very base of this organization, atoms join together to form Finally, all the Earth’s ecosystems collectively make up the the molecules, which in turn make up a cell. A cell is the smallest biosphere (Fig. 1.2, top). mushrooms sunflower bacteria ape 9,560× 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): MedioImages/PunchStock/Getty Images; (Giardia): Dr. Stan Erlandsen/CDC ISTUDY  Chapter 1 Exploring Life and Science 3 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 Species A group of similar, interbreeding organisms Organism human tree An individual; complex individuals contain organ systems Organ System nervous shoot Composed of several organs system system working together Organ the brain leaves Composed of tissues functioning together for a specific task Tissue A group of cells with a common structure and function nervous tissue leaf tissue nerve cell plant cell Cell The structural and functional unit of all living organisms methane Molecule Union of two or more atoms of the same or different elements Atom oxygen Smallest unit of an element; composed of electrons, protons, and neutrons Figure 1.2 Levels of biological organization. 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. ISTUDY  4 Chapter 1 Exploring Life and Science The ultimate source of energy for the majority of life on Earth B I O LO GY I N YO U R LI F E is the sun. Plants, algae, and some bacteria are able to harvest the How many cells are in your body? energy of the sun and convert it to chemical energy by a process called photosynthesis. Photosynthesis produces organic mole- The number of cells in a human body varies depending on the cules, such as sugars, that serve as the basis of the food chain for size of the person and whether cells have been damaged or many other organisms, including humans and all other animals. 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. Living Organisms Maintain an Internal Environment For the metabolic pathways within a cell to function correctly, the en- Life Requires Materials and Energy vironmental conditions of the cell must be kept within strict operating Humans, like all living organisms, cannot maintain their organization limits. Many of the metabolic activities of a cell, or organism, function or carry on life’s activities without an outside source of materials and in maintaining homeostasis—a constant internal environment. energy. Energy is the capacity to do work. Like other animals, In humans, many of our organ systems work to maintain humans acquire materials and energy by eating food (Fig. 1.3). homeostasis. For example, human body temperature normally fluc- Food provides nutrient molecules, which are used as building tuates slightly between 36.5 and 37.5°C (97.7 and 99.5°F) during blocks or for energy. It takes energy to maintain the organization of the day. In general, the lowest temperature usually occurs between the cell and the organism itself. Some nutrient molecules are bro- 2 a.m. and 4 a.m., and the highest usually occurs between 6 p.m. and ken down completely to provide the energy necessary to convert 10 p.m. However, activity can cause the body temperature to rise, other nutrient molecules into the parts and products of cells. The and inactivity can cause it to decline. The metabolic activities breakdown of food is a component of our metabolism, or the sum of our cells, tissues, and organs are dependent on maintaining a of all the chemical reactions that occur within a cell or organism. 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. a. 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 b. or away from a stimulus, such as the sight of food. Organisms may Figure 1.3 Humans and other animals must acquire energy. use a variety of mechanisms to move, but movement in humans All life, including humans (a) and other animals, such as this eagle and other animals is dependent on their nervous and musculoskeletal (b), must acquire energy to survive. The method by which organisms systems. The leaves of plants track the passage of the sun during acquire energy is dependent on the species. the day; when a houseplant is placed near a window, its stems bend (a): Ariel Skelley/Blend Images/Getty Images; (b): Brian E Kushner/Shutterstock to face the sun. The movement of an animal, whether self-directed ISTUDY  Chapter 1 Exploring Life and Science 5 480× a. 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. contains genes contributed by a female. The genes direct both Some behaviors help us acquire food and reproduce. growth and development so that the organism will eventually resemble the parents. Sometimes mutations, minor variations in Living Organisms Reproduce and Develop these genes, can cause an organism to be better suited for its environ- Reproduction is a fundamental characteristic of life. Cells come into ment. These mutations are the basis of evolutionary change. being only from preexisting cells, and all living organisms have parents. When organisms reproduce, they pass on their genetic Organisms Have an Evolutionary History information to the next generation. Following the fertilization of an Evolution is the process by which a population changes over time. egg by a sperm cell, the resulting zygote undergoes a rapid period of The mechanism by which evolution occurs is natural selection growth and development. This is common in most forms of life. (see Section 23.2). When a new variation arises that allows certain Figure 1.4a illustrates that an acorn progresses to a seedling before it members of a population to capture more resources, these members becomes an adult oak tree. In humans, growth occurs as the fertilized tend to survive and have more offspring than the other, unchanged egg develops into a fetus (Fig. 1.4b). Growth, recognized by an in- members. Therefore, each successive generation will include more crease in size and often in the number of cells, is a part of development. members with the new variation, which represents an adaptation In multicellular organisms, such as humans, the term development to the environment. Consider, for example, populations of humans is used to indicate all the changes that occur from the time the egg is who live at high altitudes, such as the cultures living at elevations of fertilized until death. Therefore, it includes all the changes that occur over 4,000 meters (m) (14,000 ft) in the Tibetan Plateau. This envi- during childhood, adolescence, and adulthood. Development also ronment is very low in oxygen. As the Science feature “Adapting includes the repair that takes place following an injury. to Life at High Elevations” investigates, these populations have The genetic information of all life is DNA (deoxyribonucleic evolved an adaptation that reduces the amount of hemoglobin, the acid). DNA contains the hereditary information that directs not oxygen-carrying pigment in the blood. As the feature explains, this only the structure of each cell but also its function. The information adaptation makes life at these altitudes possible. in DNA is contained within genes, short sequences of hereditary Evolution, which has been going on since the origin of life and material that specify the instructions for a specific trait. Before will continue as long as life exists, explains both the unity and reproduction occurs, DNA is replicated so an exact copy of each diversity of life. All organisms share the same characteristics of life gene may be passed on to the offspring. When humans reproduce, because their ancestry can be traced to the first cell or cells. Organ- a sperm carries genes contributed by a male into the egg, which isms are diverse because they are adapted to different ways of life. ISTUDY  6 Chapter 1 Exploring Life and Science B I O L O G Y T O D AY ► Science Adapting to Life at High Elevations Humans, like all other organisms, have an evolutionary history. Because high hemoglobin levels would be a detriment to This not only means we share common ancestors with other people at high elevations, it makes sense that natural selection would animals, but over time we demonstrate adaptations to changing favor individuals who produce less hemoglobin at high elevations. environmental conditions. One study of populations living in the Such is the case with the Tibetans in this study. Researchers have high-elevation mountains of Tibet (Fig. 1A) demonstrates how identified an allele of a gene that reduces hemoglobin production at the processes of evolution and adaptation influence humans. high elevations. Comparisons between Tibetans at both high and Normally, when a person moves to a higher altitude, the body low elevations strongly suggest that selection has played a role in may respond by making more hemoglobin, the component of blood the prevalence of the high-elevation allele. that carries oxygen, which in turn thickens the consistency of the The gene is EPSA1, located on chromosome 2 of humans. blood. For minor elevation changes, this does not present much of a EPSA1 produces a transcription factor that basically regulates problem. But for people who live at extreme elevations (some which genes are turned on and off in the body, a process called gene people in the Himalayas can live at elevations of over 13,000 ft, or expression. The transcription factor produced by EPSA1 has a num- close to 4,000 m), excess hemoglobin can present a number of health ber of functions in the body. For example, in addition to controlling problems, including chronic mountain sickness, a disease that the amount of hemoglobin in the blood, this transcription factor also affects people who live at high altitudes for extended periods of time. regulates other genes that direct how the body uses oxygen. The problem is that, as the amount of hemoglobin increases, the When the researchers examined the variations in EPSA1 in the blood thickens and becomes more viscous. This can cause elevated Tibetan population, they discovered that the Tibetan version greatly blood pressure, or hypertension, and an increase in the formation reduces the production of hemoglobin. Therefore, the Tibetan popula- of blood clots, both of which have negative physiological effects. 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 EPSA1 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 Figure 1A High-elevation adaptations. 1. What other environments do you think could be studied to Individuals living at high elevations, such as Tibetans, have become look for examples of human adaptation? adapted to their high-elevation environment. 2. In addition to hemoglobin levels, do you think people at high Michael Freeman/Corbis elevations may exhibit other adaptations? C O N N E C TI N G TH E C O N C E P T S Both homeostasis and evolution are central themes in the study of biology. For more examples of homeostasis and evolution, CHECK YOUR PROGRESS 1.1 refer to the following discussions: 1. List the basic characteristics of life. Section 4.8 explains how body temperature is regulated. 2. Summarize the levels of biological organization. Section 11.4 explores the role of the kidneys in fluid and salt 3. Explain the relationship between adaptations and homeostasis. evolutionary change. Section 23.3 examines the evolutionary history of humans. ISTUDY  Chapter 1 Exploring Life and Science 7 that possess a nucleus. Some of these organisms are single-celled; 1.2 Humans Are Related others are multicellular. Humans are an example of multicelled to Other Animals Eukarya. Historically, domain Eukarya was divided into one of four LE AR N I N G OUTCO M E S kingdoms (Fig. 1.6). However, the development of improved Upon completion of this section, you should be able to techniques in analyzing the DNA of organisms suggests that not all of the Protistas (the earliest eukaryotes) share the same 1. Summarize the place of humans in the overall classification of living organisms. evolutionary lineage, meaning that the evolution of the eukary- 2. Understand that humans have a cultural heritage. otes has occurred along several paths. A new taxonomic group, 3. Describe the relationship between humans and the called a supergroup, was developed to explain these evolution- biosphere. 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 Biologists classify all life as belonging to one of three domains. relationships between these organisms. While these relation- The evolutionary relationships of these domains are presented in ships are still being studied and analyzed, current thinking Figure 1.5. places the animals in the same supergroup (the Opisthikonts) as Two of these domains, domain Bacteria and domain Archaea, the fungi. contain prokaryotes, single-celled organisms that lack a nucleus The traditional kingdom level of classification within domain (Fig. 1.6). Organisms in the third domain, Eukarya, all contain cells Eukarya is still widely used, and is often placed beneath the BACTERIA common ancestor ARCHAEA (first cells) Protists Plants EUKARYA Fungi domains kingdoms Animals common ancestor 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 Billions of Years Ago (BYA) 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). ISTUDY  8 Chapter 1 Exploring Life and Science Domain Archaea Domain Bacteria Prokaryotic cells Prokaryotic cells of various shapes of various shapes Adaptations to Adaptations to extreme environments all environments Absorb or Absorb, photosynthesize, chemosynthesize food or chemosynthesize food Unique chemical Unique chemical characteristics characteristics 33,200× 6,600× Sulfolobus, an archaean Escherichia coli, a bacterium Domain Eukarya; Kingdom Protista Domain Eukarya: Kingdom Plantae Algae, protozoans, Certain algae, mosses, ferns, slime molds, and conifers, and flowering plants water molds Multicellular, usually with Complex single cell specialized tissues, (sometimes filaments, containing complex cells colonies, or even Photosynthesize food multicellular) Absorb, photosynthesize, 160× or ingest food Ophrys apifera, bee orchid Paramecium, a single-celled protozoan Domain Eukarya: Kingdom Fungi Domain Eukarya: Kingdom Animalia Molds, mushrooms, yeasts, Sponges, worms, insects, and ringworms fishes, frogs, turtles, Mostly multicellular filaments birds, and mammals with specialized, complex cells Multicellular with Absorb food specialized tissues containing complex cells Ingest food Buteo jamaicensis, red-tailed hawk Amanita muscaria, a mushroom Figure 1.6 The classification of life. 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 ∙ Kingdom Animalia. Animals are multicellular organisms that Figure 1.6 and include the following: must ingest and process their food. They are capable of motion at some point in their life cycle. ∙ Kingdom Protista. Commonly called the protists, this is a very diverse group of eukaryotic organisms, ranging from Among the animals are the invertebrates, which lack an inter- single-celled forms to a few multicellular organisms. Some nal skeletal support structure, called vertebrae. Most animals are protists use photosynthesis to manufacture food, and some invertebrates. Examples include earthworms, insects, and mollusks. must acquire their own food. As we mentioned, the diverse Vertebrates are animals that have a nerve cord protected by a verte- nature of these organisms indicates they have multiple evolu- bral column, which gives them their name. Fish, reptiles, amphibi- tionary origins, and thus belong to different supergroups. ans, and birds are all examples of vertebrates. Vertebrates with hair ∙ Kingdom Plantae. The plants are multicellular, photosyn- or fur and mammary glands are classified as mammals. Humans, thetic organisms. raccoons, seals, and meerkats are examples of mammals. ∙ Kingdom Fungi. Fungi are the familiar molds and mush- Humans are primate mammals and are most closely related to rooms that help decompose dead organisms. Some fungi are apes. We are distinguished from apes by our (1) highly developed parasites of plants and animals. brains, (2) completely upright stance, (3) creative language, and ISTUDY  Chapter 1 Exploring Life and Science 9 (4) ability to use a wide variety of tools. Humans did not evolve from apes; apes and humans share a common, apelike ancestor. CHECK YOUR PROGRESS 1.2 Today’s apes are our evolutionary cousins. Our relationship to 1. Define the term biosphere. apes is analogous to you and your first cousin being descended 2. Define culture. from your grandparents. We could not have evolved directly from 3. Explain why humans belong to the domain Eukarya and our cousins, because we are contemporaries—living on Earth at kingdom Animalia. the same time. Humans Have a Cultural Heritage C O N N E C TI N G TH E C O N C E P T S Humans have a cultural heritage in addition to a biological heri- To learn more about the preceding material, refer to the following tage. Culture encompasses human activities and products passed discussions: on from one generation to the next outside of direct biological Chapter 23 examines recent developments in the study of inheritance. Among animals, only humans have a language that al- human evolution. lows us to communicate information and experiences symbolically. Chapter 24 provides a more detailed look at ecosystems. We are born without knowledge of an accepted way to behave, but Chapter 25 explores how humans interact with the biosphere. 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 1.3 Science as a Process wild to how to use a computer. Human skills have also produced a rich heritage in the arts and sciences. However, a society highly LE A R N I N G OUTCO M E S dependent on science and technology has its drawbacks as well. Upon completion of this section, you should be able to Unfortunately, this cultural development may mislead us into be- 1. Describe the general process of the scientific method. lieving that humans are somehow not part of the natural world 2. Distinguish between a control group and an experimental surrounding us. group in a scientific test. 3. Recognize the importance of scientific journals in the Humans Are Members of the Biosphere reporting of scientific information. All life on Earth is part of the biosphere, the living network that 4. Recognize the importance of statistical analysis to the study of science. 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 Science is a way of knowing about the natural world. When scien- microorganisms that decompose, the waste we create would soon tists study the natural world, they aim to be objective, rather than cover the Earth’s surface. Some species of bacteria help us by subjective. Objective observations are supported by factual informa- cleaning up pollutants like heavy metals and pesticides. tion, whereas subjective observations involve personal judgment. Freshwater ecosystems, such as rivers and lakes, provide fish For example, the fat content of a particular food would be an to eat, water to drink, and water to irrigate crops. Many of our objective observation of a nutritional study. Reporting about the crops and prescription drugs were originally derived from plants good or bad taste of the food would be a subjective observation. that grew naturally in an ecosystem. Some human populations It is difficult to make objective observations and conclusions, around the globe still depend on wild animals as a food source. The because we are often influenced by our prejudices. Scientists must water-holding capacity of forests prevents flooding, and the ability keep in mind that scientific conclusions can change because of of forests and other ecosystems to retain soil prevents soil erosion. new findings. New findings are often made because of recent For many people, these forests provide a place for recreational advances in techniques or equipment. activities like hiking and camping. 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, B I O LO GY I N YO U R LI F E because the scientific process employs the scientific method, a standard series of steps used in gaining new knowledge that is How many humans are there? widely accepted among scientists. The scientific method (Fig. 1.7) In 2021, it was estimated there were over 7.9 billion humans on acts as a guideline for scientific studies. the planet. Each human needs food, shelter, clean water and air, The approach of individual scientists to their work is as varied and materials to maintain a healthy lifestyle. Our species adds as the scientists. However, much of the scientific process is de- an additional 83 million people per year—that is like adding the scriptive. For example, an observation of a new disease may lead a population of ten New York Cities annually! This makes human scientist to describe all the aspects of the disease, such as the envi- population growth one of the greatest threats to the biosphere. ronment, the age of onset, and the characteristics of the disease. Some areas of biology, such as the study of biodiversity in the ISTUDY  10 Chapter 1 Exploring Life and Science Observation Hypothesis 1 Potential Hypothesis 2 hypotheses Reject Hypothesis 3 Prediction Experiment hypothesis 1 Remaining Reject possible Hypothesis 2 Prediction Experiment Hypothesis 3 hypothesis 2 hypotheses Last remaining Figure 1.7 The scientific method. possible Hypothesis 3 On the basis of new and/or previous observations, hypothesis Modify hypothesis a scientist formulates a hypothesis. The hypothesis is used to develop predictions to be tested by Predictions further experiments and/or observations, and new data either support or do not support the hypothesis. Following an experiment, a scientist Experiment 1 Experiment 2 Experiment 3 Experiment 4 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, Predictions studies pertaining to development, anatomy, and Conclusion confirmed fossil remains all support the theory of evolution. ecological sciences (see Section 1.4), lend themselves more to this examining a petri dish of bacteria that had accidentally become descriptive approach. Regardless of their area of study, most scien- contaminated with the mold Penicillium, Alexander Fleming ob- tists spend a considerable amount of time performing a descriptive served an area around the mold that was free of bacteria. Fleming analysis of their observation before proceeding into the steps of the had long been interested in finding cures for human diseases scientific method. Scientists often modify or adapt the process to caused by bacteria, and he was very knowledgeable about antibac- suit their particular field of study, but for the sake of discussion, it terial substances. So when Fleming saw the dramatic effect of is useful to think of the scientific method as consisting of certain Penicillium mold on bacteria, he reasoned that the mold might be logical steps. producing an antibacterial substance. We call such a possible explanation for a natural event a Start with an Observation hypothesis. A hypothesis is based on existing knowledge, so it is much more informed than a mere guess. Fleming’s hypothesis was Scientists believe that nature is orderly and measurable—that natu- supported by further study, but sometimes a hypothesis is not sup- ral laws, such as the law of gravity, do not change with time—and ported and must be either modified and subjected to additional that a natural event, or phenomenon, can be understood more fully study or rejected. When thinking about how to test the hypothesis, through observation—a formal way of watching the natural world. the scientist may make a prediction, or an expected outcome, Observations may be made with the senses, such as sight and based on knowledge of the factors involved in the observation. smell, or with instruments; for example, a microscope enables us to All of a scientist’s past experiences, no matter what they might see objects that could never be seen by the naked eye. Scientists may be, may influence the formation of a hypothesis. But a scientist expand their understanding even further by taking advantage of the considers only hypotheses that can be tested by experiments or knowledge and experiences of other scientists. For instance, they further observations. Moral and religious beliefs, although very may look up past studies on the Internet or at the library, or they may important to our lives, differ among cultures and through time and write or speak to others who are researching similar topics. are not always testable. Develop a Hypothesis Test the Hypothesis After making observations and gathering knowledge about a Scientists often perform an experiment, which is a series of proce- phenomenon, a scientist uses inductive reasoning. Inductive dures, to test a hypothesis. To determine how to test a hypothesis, reasoning occurs whenever a person uses creative thinking to a scientist uses deductive reasoning. Deductive reasoning combine isolated facts into a cohesive whole. Chance alone can involves “if... then” logic. help a scientist arrive at an idea. The most famous case pertains to The manner in which a scientist intends to conduct an experi- the antibiotic penicillin, which was discovered in 1928. While ment is called the experimental design. A good experimental design ISTUDY  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 64× variation in the concentration of blood cholesterol over a 4-week Drosophila melanogaster Caenorhabditis elegans 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 Arabidopsis thaliana Mus musculus them evaluate their experimental data. In statistics, the standard Figure 1.8 Model organisms used in scientific studies. error, or standard deviation, tells us how uncertain a particular Drosophila melanogaster is used as a model organism in the study value is. Suppose you predict how many hurricanes Florida will of genetics. Mus musculus is used in the study of medicine. have next year by calculating the average number during the past Caenorhabditis elegans is used by developmental biologists, and 10 years. If the number of hurricanes per year varies widely, your Arabidopsis thaliana is used by botanists to understand plant genetics. standard error will be larger than if the number per year is usually (Drosophila): janeff/iStockphoto/Getty Images; (C. elegans): Sinclair Stammers/ about the same. In other words, the standard error tells you how far Science Source; (Arabidopsis): Wildlife GmbH/Alamy Stock Photo; (M. musculus): off the average could be. If the average number of hurricanes is Redmond Durrell/Alamy Stock Photo four and the standard error is ±2, then your prediction of four hurricanes is between two and six hurricanes. In Figure 1.9, the ensures that scientists are examining the contribution of a specific standard error is represented by the bars above and below each data variable, called the experimental variable, to the observation. The point. This provides a visual indication of the statistical analysis of result is termed the responding variable, or dependent variable, the data. 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 Variation in Blood Cholesterol Levels to the experimental variable, but the control group is not. If the 225 control group and test groups show the same results, the experi- menter knows that the hypothesis predicting a difference between Blood Cholesterol (mg/dl) them is not supported. standard error Scientists often use model organisms and model 200 systems to test a hypothesis. Some common model organ- isms are shown in Figure 1.8. Model organisms are chosen y-axis because they allow the researcher to control aspects of Data 175 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 150 may not be possible in the natural environment. For example, Week 1 Week 2 Week 3 Week 4 ecologists may use computer programs to model how human activities will affect the climate of a specific ecosystem. While x-axis models provide useful information, they do not always answer the original question completely. For example, medicine that is effec- Figure 1.9 The presentation of scientific data. tive in mice ideally should be tested in humans, and ecological This line graph shows the variation in the concentration of blood experiments conducted using computer simulations need to be cholesterol over a 4-week study. The bars above and below the data verified by actual field experiments. points represent the variation, or standard error, in the results. ISTUDY  12 Chapter 1 Exploring Life and Science Statistical Significance Scientific Theory When scientists conduct an experiment, there is always the possibil- The ultimate goal of science is to understand the natural world in ity that the results are due to chance or to some factor other than the terms of scientific theories, which are accepted explanations for experimental variable. Investigators take into account several factors how the world works. Some of the basic theories of biology are when they calculate the probability value (p) that their results were the cell theory, which says that all organisms are composed of due to chance alone. If the probability value is low, researchers cells; the gene theory, which says that inherited information in a describe the results as statistically significant. A probability value of gene contributes to the form, function, and behavior of organisms; less than 5% (usually written as p < 0.05) is acceptable; even so, and the theory of evolution, which says that all organisms have a keep in mind that the lower the p value, the less likely it is that the common ancestor and that each organism is adapted to a particu- results are due to chance. Therefore, the lower the p value, the greater lar way of life. the confidence the investigators and you can have in the results. The theory of evolution is considered the unifying concept Depending on the type of study, most scientists like to have a p value of biology, because it pertains to many different aspects of or- of < 0.05, but p values of < 0.001 are common in many studies. ganisms. For example, the theory of evolution enables scientists to understand the history of life, the variety of organisms, and Scientific Publications the anatomy, physiology, and development of organisms. The theory of evolution has been a very fruitful scientific theory, Scientific studies are customarily published in scientific journals, meaning it has helped scientists generate new testable hypotheses. such as Science or Nature, so that all aspects of a study are avail- Because this theory has been supported by so many observations able to the scientific community. Before information is published and experiments for over 100 years, some biologists refer to in scientific journals, it is typically reviewed by experts, who the theory of evolution as the principle of evolution, a term ensure that the research is credible, accurate, unbiased, and well sometimes used for theories that are generally accepted by an executed. Another scientist should be able to read about an experi- overwhelming number of scientists. Others prefer the term law ment in a scientific journal, repeat the experiment in a different instead of principle. 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 An Example of a Controlled Study manner in which it was conducted. This process of rejection is As presented in the Science feature "Discovering the Cause of important in science because it causes researchers to critically Ulcers," we now know that most stomach and intestinal ulcers review their hypotheses, predictions, and experimental designs, so (open sores) are caused by the bacterium Helicobacter pylori. that their next attempt will more adequately address their hypoth- esis. Often, it takes several rounds of revision before research is Experimental Design accepted for publication in a scientific journal. People should be especially careful about scientific information Let’s say investigators want to determine which of two antibiotics available on the Internet, which is not well regulated. Reliable, cred- is best for the treatment of an ulcer. When clinicians do an experi- ible scientific information can often be found at websites with URLs ment, they try to vary just the experimental variables—in this case, containing.edu (for educational institution),.gov (for government the medications being tested. Each antibiotic is administered to an sites such as the National Institutes of Health or the Centers for Dis- independent test group. The control group is not given an antibi- ease Control and Prevention), and.org (for nonprofit organizations, otic. If by chance the control group shows the same results as one such as the American Lung Association or the National Multiple of the test groups, the investigators may conclude that the anti- Sclerosis Society). Unfortunately, quite a bit of scientific informa- biotic in that test group is ineffective, because it does not show a tion on the Internet is intended to entice people into purchasing result that is significantly different from that of the control group. some sort of product for weight loss, prevention of hair loss, or simi- The study depicted in Figure 1.10a shows how investigators may lar maladies. These websites usually have URLs ending with.com study this hypothesis: or.net. It pays to question and verify the information from these Hypothesis: Newly discovered antibiotic B is a better treatment websites with another source (a primary source, if possible). for ulcers than antibiotic A, which is in current use. In any experiment, it is important to reduce the number of Develop a Conclusion possible variables (differences). In this experiment, those variables Scientists must analyze the data in order to reach a conclusion may include factors such as differences in the subjects’ sex, weight, about whether a hypothesis is supported or not. Because science and previous illnesses. Therefore, the investigators randomly di- progresses, the conclusion of one experiment can lead to the hy- vide a large group of volunteers equally into experimental groups. pothesis for another experiment (see Fig. 1.9). In other words, The hope is that any differences will be distributed evenly among results that do not support one hypothesis can often help a scientist the three groups. The larger the number of volunteers (the sample formulate another hypothesis to be tested. Scientists report their size), the greater the chance of reducing the influence of external findings in scientific journals, so that their methodology and data variables. This is why many medical studies involve thousands are available to other scientists. of individuals. ISTUDY  Chapter 1 Exploring Life and Science 13 State Hypothesis: After the investigators have determined that all volunteers do Antibiotic B is a better treatment for have ulcers, they will want the subjects to think they are all receiv- ulcers than antibiotic A. 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 Perform Experiment: intestinal linings of each subject to determine if ulcers are still Groups were treated the same except as noted. 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. Control group: Test group 1: Test group 2: Because endoscopy is somewhat subjective, it is probably best received received received if the examiner is not aware of which group the subject is in; oth- placebo antibiotic A antibiotic B erwise, examiner prejudice may influence the examination. When neither the patient nor the technician is aware of the specific treat- Analyze the Data: ment, it is called a double-blind study. Graph the data to analyze for statistical differences. In this study, the investigators may decide to determine the effectiveness of the medication by the percentage of people who a. Experimental design no longer have ulcers. So, if 20 people out of 100 still have ulcers, Effectiveness of Treatment the medication is 80% effective. The difference in effectiveness is 100 easily read in the graph portion of Figure 1.10b. 80 Conclusion: On the basis of their data, the investigators conclude that their hypothesis has been supported. % Treated 60 40 80 60 20 CHECK YOUR PROGRESS 1.3 10 0 1. Describe each step of the scientific method. Control Test Test 2. Explain why a controlled study is an important part of the Group Group 1 Group 2 experimental design. b. Experimental data 3. List a few pros and cons of using a scientific journal Figure 1.10 Example of a controlled study. versus other sources of information. a. The experimental design of the controlled study. b. The experimental 4. Summarize how the use of graphs and statistics aids in data displayed as a graph showing that medication B was a more data analysis. effective treatment than medication A for the treatment of ulcers. (students, all photos): René Mansi/E+/Getty Images C O N N E C TI N G TH E C O N C E P T S In this experiment, the researchers divide the individuals into For more information on the topics presented in this section, refer to the following discussions: three groups: Section 8.4 discusses how resistance to antibiotics occurs. Control group: Subjects with ulcers are not treated with either Section 9.3 provides more information on ulcers. antibiotic. Figure 14.4 shows the relationship between an action Test group 1: Subjects with ulcers are treated with antibiotic A. potential and voltage across a plasma membrane. Test group 2: Subjects with ulcers are treated with antibiotic B. ISTUDY  14 Chapter 1 Exploring Life and Science B I O L O G Y T O D AY ► 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 16,000× hypothesis: H. pylori is the cause of gastritis and ulcers. Marshall decided to make use of Koch’s postulates, the stan- Helicobacter pylori dard criteria that must be fulfilled to show that a pathogen (bacte- rium or virus) causes a disease: Figure 1B The cause of stomach ulcers. Research by Dr. Barry Marshall showed that stomach ulcers (left) are ∙ The suspected pathogen (virus or bacterium) must be present often caused by Helicobacter pylori (right). in every case of the disease. (ulcer): Dr. E. Walker/Science Source; (H. pylori): Heather Davies/Science Photo Library/Science Source ∙ 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- symptoms abated without need for medication, and they never mentally infected host. developed an ulcer. Marshall challenged the scientific community to refute his hypothesis. Many tried, but ultimately the investigators By 1983, Marshall had fulfilled the first and second of Koch’s cri- supported his findings. teria. He was able to isolate H. pylori from patients with ulcers and In science, many experiments, often involving a considerable grow it in the laboratory. Despite Marshall’s presentation of these number of subjects, are required before a conclusion can be findings to the scientific community, most physicians continued to reached. By the early 1990s, at least three independent studies in- believe that stomach acidity and stress were the causes of stomach volving hundreds of patients had been published showing that anti- ulcers. In those days, patients were usually advised to make drastic biotic therapy can eliminate H. pylori from the intestinal tract and changes in their lifestyle to cure their ulcers. Many scientists cure patients of ulcers wherever they occurred in the tract. believed that no bacterium would be able to survive the normal Dr. Marshall and Dr. Warren received a Nobel Prize in acidity of the stomach. Physiology or Medicine in 2005. The Nobel committee reportedly Marshall had a problem in fulfilling the third and fourth of thanked Marshall and Warren for their “pioneering discovery,” Koch’s criteria. He had been unable to infect guinea pigs and rats stating that peptic ulcer disease now could be cured with antibiot- with the bacteria, because the bacteria did not flourish in the intes- ics and acid-secretion inhibitors rather than becoming a “chronic, tinal tracts of those animals. Marshall was not able to use human frequently disabling condition.” 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 Questions to Consider solution of H. pylori. Within the week, they felt lousy and were 1. Explain how Marshall’s approach was similar to, and different vomiting up their stomach contents. Examination by endoscopy from, the scientific method shown in Figure 1.7. showed that their stomachs were now inflamed, and biopsies of the 2. How could Marshall have done this experiment if he had an stomach lining contained the suspected bacterium (Fig. 1B). Their animal model to work with? ISTUDY  Chapter 1 Exploring Life and Science 15 amount that remains in the atmosphere. It is believed that most 1.4 Science and the Challenges of this dissolves in the oceans, which are increasing in acidity. Facing Society The increased amount of carbon dioxide (and other gases) in the atmosphere is causing a rise in temperature called global warming. LE AR N I N G OUTCO M E S These gases allow the sun’s rays to pass through them, but they Upon completion of this section, you should be able to then absorb and radiate heat back to Earth, a phenomenon called the greenhouse effect. 1. Distinguish between science and technology. There is a consensus among scientists from around the globe 2. Summarize some of the major challenges facing science. that climate change and global warming are causing significant changes in many of the Earth’s ecosystems and represent one of As we have learned in this chapter, science is a systematic way of the greatest challenges of our time. Throughout this text, we will acquiring knowledge about the natural world. Science is a slightly return to see how climate change is impacting humans, from the different endeavor than technology. Technology is the application loss of biodiversity to increases in the rates of certain types of of scientific knowledge to the interests of humans. Scientific human disease. We will examine climate change in more detail in investigations are the basis for the majority of our technological Chapters 24 and 25. 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 Biodiversity and Habitat Loss facing science, technology, and society. The term biodiversity represents the total number and relative abundance of species, the variability of their genes, and the dif- Climate Change ferent ecosystems in which they live. The biodiversity of our The overwhelming consensus within the scientific community planet has been estimated to be around 8.7 million species (not is that the single greatest challenge facing science and society, counting bacteria), and so far, approximately 2.3 million have and the greatest threat to both humans and the environment, is been identified and named. Extinction is the death of a species climate change. The term climate change refers to changes in or larger classification category. It is estimated that presently we the normal cycles of the Earth’s climate that may be attributed are losing hundreds of species every year due to human activities to human activity. Climate change is primarily due to an imbal- and that as much as 27% of all identified species, including most ance in the chemical cycling of the element carbon. Normally, primates, birds, and amphibians, may be in danger of extinction carbon is cycled within an ecosystem (see Section 24.3). How- before the end of the century. In many cases, these extinctions are ever, due to human activities, more carbon dioxide is being accelerated by a combination of habitat loss and climate change released into the atmosphere than is being removed. In 1850, (Fig. 1.12). Many biologists are alarmed about the present rate of atmospheric CO2 was at about 280 parts per million (ppm). extinction and hypothesize it may eventually rival the rates of the Today, it is over 415 ppm (Fig. 1.11). This increase is largely five mass extinctions that occurred during our planet’s history. due to the burning of fossil fuels and the destruction of forests The last mass extinction, about 65 million years ago, caused to make way for farmland and pastures. The amount of carbon many plant and animal species, including the dinosaurs, to dioxide released into the atmosphere today is about twice the become extinct. The two most biologically diverse ecosystems— tropical rain forests and coral reefs—are home to 415 many organisms. These ecosystems are also threat- ened by human activities. The canopy of the tropical 410 rain forest alone supports a variety of organisms, in- CO2 (parts per million) 405 cluding orchids, insects, and monkeys. Coral reefs, 400 which are found just offshore of the continents and islands near the equator, are built up from calcium 395 carbonate skeletons of sea animals called corals. 390 Reefs provide a habitat for many animals, including 385 jellyfish, sponges, snails, crabs, lobsters, sea turtles, moray eels, and some of the world’s most colorful 380 fishes. Like tropical rain forests, coral reefs are se- 2006 2008 2010 2012 2014 2016 2018 2020 verely threatened as the human population increases Year in size. Some reefs are 50 million years old, yet in just a few decades, human activities have destroyed an es- Figure 1.11 Increases in atmospheric carbon dioxide concentrations. timated 25% of all coral reefs and seriously degraded The global average carbon dioxide (CO2) concentration now exceeds 415 ppm and is another 30%. At this rate, nearly three-quarters could the major contributing factor to climate change and global warming. be destroyed within 40 years. Similar statistics are NOAA, “Global Climate Change: Facts.” http://climate.nasa.gov/vital-signs/carbon-dioxide/. available for tropical rain forests. ISTUDY  16 Chapter 1 Exploring Life and Science 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