A View of Life
Chapter 
1
Outline
	1.1	The Unity and Diversity of Life
	•	Although life is quite diverse, living things share certain characteristics.2
	•	Living things have several levels of 
organization.2
	•	All living things have characteristics in common because they are descended from a common ancestor, and they are diverse because they exhibit these characteristics in unique ways.4
	1.2	How the Biosphere Is Organized 
	•	The biosphere is made up of ecosystems where living things interact with each other and with the physical environment.5
	1.3	How Organisms Are Classified
	•	Living things are classified into categories according to their evolutionary relationships.6
	•	Biologists are concerned about the current rate of extinctions and believe that we should take all possible steps to preserve biodiversity.7
	1.4	Science As a Way of Knowing
	•	The scientific process includes a method to gather information and to make conclusions about the natural world.8
	•	Various conclusions pertaining to the same area of interest sometimes allow scientists to arrive at a theory, a general concept about the natural world.9
	1.5	Science and Society
	•	All citizens have to be prepared to make value judgments about the use of technology.12
It is hard to believe that the number of bacterial organisms living on your skin right now is greater than the number of human organisms living on this planet. How can more than 6 billion individual organisms live on the surface of your skin? The answer is that bacterial cells are extremely small—so small that we tend not to think of them. Because most people cringe at the thought of “germs,” a stroll through just about any aisle of your local grocery store will reveal a slew of products that claim to be antibacterial. Advertisers tend to make us think that all bacteria are harmful. But only a handful of bacterial species are actually dangerous to humans, while the overwhelming majority are beneficial. The billions of bacteria that live on your skin right now are termed normal flora (or resident bacteria), and they essentially occupy all the available space on your skin surface. Should a detrimental bacterium come along, it will literally have no room to settle and multiply. Because the normal flora protect you in this way, we certainly don't want to do away with them.
The bacterial cells occupying your skin have a lot in common with the cells that make up your body. This chapter introduces the common characteristics, the diversity, and the organization of living things, as well as explaining how scientists perform their studies.
1.1		The Unity and Diversity of Life 
From huge menacing sharks to miniscule exotic orchids, life is very diverse.Despite life’s diversity, all living things, also called organisms, share certain characteristics, and these characteristics give us insight into the nature of life and help distinguish organisms from nonliving things.
Living Things Are Organized
The complex organization of living things begins with small molecules that join to form larger molecules within a cell, the smallest, most basic unit of life. Although a cell is alive it is made from nonliving molecules. 
Some organisms are unicellular, being only a single cell. Plants and animals are multicellular and are composed of many types of cells. In multicellular organisms, similar cells combine to form tissues. Tissues make up organs, as when various -tissues combine to form a heart or a leaf. Organs work together in organ systems; for example, the heart and blood vessels form the cardiovascular system. Various organ systems work together within complex organisms (Fig. 1.1).
Later in this chapter, we will see that levels of biological organization extend beyond the individual organism. For example, all the members of one species in a particular area belong to a population. Zebras form one of the many populations on an African plain. All the populations make up a community. The community of populations interacts with the physical environment to form an ecosystem. Finally, all the Earth’s ecosystems make up the biosphere.
Living Things Acquire Materials and Energy
Living things cannot maintain their organization or carry on life’s activities without an outside source of materials and energy (Fig. 1.2). Food provides nutrient molecules, which are used as building blocks or energy sources. Energy is the capacity to do work, and it takes work to maintain the organization of the cell and the organism. When cells use nutrient molecules to make their parts and products, they carry out a sequence of chemical reactions. The term metabolism encompasses all the chemical reactions that occur in a cell.
The ultimate source of energy for nearly all life on Earth is the sun. Plants and certain other organisms are able to capture solar energy and carry on photosynthesis, a process that transforms solar energy into the chemical energy of nutrient molecules. Animals and plants get energy by metabolizing nutrient molecules made by photosynthesizers.
Remaining Homeostatic
For metabolic processes to continue, living things need to keep themselves stable in temperature, moisture level, acidity, and other physiological factors. This is homeostasis—the maintenance of internal conditions within certain boundaries.
Many organisms depend on behavior to regulate their internal environment. A chilly lizard may raise its internal temperature by basking in the sun on a hot rock. When it starts to overheat, it scurries for cool shade. Other organisms have control mechanisms that do not require any -conscious activity. When a student is so engrossed in her textbook that she forgets to eat lunch, her liver releases stored sugar to keep the blood sugar level within normal limits. Hormones regulate sugar storage and release, but in other instances the nervous system is involved in maintaining homeostasis.
Living Things Respond
Living things find energy and/or nutrients by interacting with their surroundings. Even unicellular organisms can respond to their environment. The beating of microscopic hairs or the snapping of whiplike tails moves them toward or away from light or chemicals. Multicellular organisms can manage more complex responses. A monarch butterfly can sense the approach of fall and begin its flight south where resources are still abundant. A vulture can smell meat a mile away and soar toward dinner. 
The ability to respond often results in movement: The leaves of a plant turn toward the sun, and animals dart toward safety. Appropriate responses help ensure survival of the organism and allow it to carry on its daily activities. Altogether, we call these activities the behavior of the organism.
Living Things Reproduce and Develop
Life comes only from life. Every type of living thing can -reproduce, or make another organism like itself. Bacteria and other types of unicellular organisms simply split in two. In multicellular organisms, the reproductive process usually begins with the pairing of a sperm from one partner and an egg from the other partner. The union of sperm and egg, followed by many cell divisions, results in an immature individual, which grows and develops through various stages to become an adult.
An embryo develops into a whale or a yellow daffodil or a human being because of the specific set of genes inherited from its parents (Fig. 1.3). In all organisms, the genes are made of long DNA (deoxyribonucleic acid) molecules, but even so the genes are different between species and individuals. DNA provides the blueprint or instructions for the organization and metabolism of the particular organism. All cells in a multicell-ular organism contain the same set of genes, but only certain ones are turned on in each type of specialized cell. 
Living Things Have Adaptations
Adaptations are modifications that make organisms suited to their way of life. Some hawks have the ability to catch fish (Fig. 1.2), and others are best at catching rabbits (Fig. 1.4). Hawks can fly in part because they have hollow bones to reduce their weight and flight muscles to depress and elevate their wings. When a hawk dives, its strong feet take the first shock of the landing, and its long, sharp claws reach out and hold onto the prey. 
Organisms become modified over time by a process called natural selection. Certain members of a species, defined as a group of interbreeding individuals, may inherit a genetic change that causes them to be better suited to a particular environment. These members can be expected to produce more surviving offspring that also have the favorable characteristic. In this way, the attributes of the species’ members change over time.
Descent with Modification
The unity of living things extends beyond those characteristics that are observable by the human eye. As mentioned, every organism’s genes are composed of DNA, and organisms carry out the same metabolic reactions to acquire energy and maintain their organization. This unity suggests that all living things are descended from a common ancestor—the first cell or cells. 
Evolution is descent with modification. One species can be a common ancestor to several species, each adapted to a particular set of environmental conditions. Specific adaptations allow species to play particular roles in an ecosystem. The diversity of life-forms is best understood in terms of the many different ways in which organisms carry on their life functions within the ecosystem where they live, acquire energy, and reproduce.
1.2		How the Biosphere 
Is Organized
The organization of life extends beyond the individual to the biosphere, the zone of air, land, and water at the surface of the Earth where living organisms are found. Individual organisms belong to a population, all the members of a species within a particular area. The populations within a community interact among themselves and with the physical environment (soil, atmosphere, etc.), thereby forming an ecosystem.
Ecosystem
One example of an ecosystem is a North American grassland, which is inhabited by populations of rabbits, hawks, and various types of grasses, among many others. These populations interact with each other by forming food chains in which one population feeds on another. For example, rabbits feed on grasses, while hawks feed on rabbits and other organisms.
As Figure 1.4 shows, ecosystems are characterized by chemical cycling and energy flow, both of which begin when producers, such as grasses, take in solar energy and inorganic nutrients to produce food (organic nutrients) by photosynthesis. Chemical cycling (aqua arrows) occurs as chemicals move from one consumer population to another in a food chain, until with death, decomposers return inorganic nutrients to the producers once again. Energy, on the other hand, flows from the sun through plants and the other members of the food chain as they feed on one another. The energy gradually dissipates and returns to the atmosphere as heat (red arrows). Because energy does not cycle, ecosystems could not stay in existence without solar energy and the ability of photosynthesizers to absorb it.
Biosphere
Climate largely determines where different ecosystems are found in the biosphere. For example, deserts exist in areas of -minimal rain, while forests require much rain. The two most biologically diverse ecosystems—tropical rain forests and coral reefs—occur where solar energy is most abundant. The human population tends to modify these and all ecosystems for its own purposes. Humans clear forests or grasslands in order to grow crops; later, they build houses on what was once farmland; and finally, they convert small towns into cities. As coasts are developed, humans send sediments, sewage, and other pollutants into the sea and onto coral reefs.
Tropical rain forests, coral reefs, and most ecosystems are severely threatened as the human population increases in size. Some coral reefs are 50 million years old, and yet in just a few decades, human activities have destroyed 10% of all reefs and seriously degraded another 30%. At this rate, nearly three-quarters could be destroyed within 50 years. Similar statistics are available for tropical rain forests.
It has long been clear that human beings depend on healthy ecosystems for food, medicines, and various raw materials. We are only now beginning to realize that we depend on them even more for the services they provide. The workings of ecosystems ensure that environmental conditions are suitable for the continued existence of humans. 
1.3		How Organisms Are Classified
Because life is so diverse, it is helpful to have a system that groups organisms into categories. Taxonomy is the discipline of identifying and classifying organisms according to certain rules. Taxonomy makes sense out of the bewildering variety of life on Earth by classifying organisms according to their presumed evolutionary relationship. As more is learned about evolutionary relationships between species, taxonomy changes. Taxonomists are even now making observations and performing experiments that will one day bring about changes in the classification system adopted by this text.
Categories of Classification
The classification categories, going from least inclusive to most inclusive, are species, genus, family, order, class, phylum, kingdom, and domain. Each successive category above species contains more types of organisms than the preceding one. Species placed within one genus share many specific characteristics and are the most closely related, while species placed in the same domain share only general characteristics. For example, all species in the genus Pisum look pretty much the same—that is, like pea plants—but species in the plant kingdom can be quite varied, as is evident when we compare grasses to trees. By the same token, only modern humans are in the genus Homo, but many types of species, from tiny hydras to huge whales, are members of the animal kingdom. Species placed in different domains are the most distantly related. 
Domains
Biochemical evidence suggests that there are only three domains: domain Bacteria, domain Archaea, and domain Eukarya. Both domain Bacteria and domain Archaea contain prokaryotes. Prokaryotes are unicellular, and they lack the membrane-bounded nucleus found in the eukaryotes of domain -Eukarya. 
Prokaryotes are structurally simple (Figs. 1.5 and 1.6) but metabolically complex. Archaea live in aquatic environments that lack oxygen or are too salty, too hot, or too acidic for most other organisms. Perhaps these environments are similar to those of the primitive Earth, and -archaea are representative of the first cells that evolved. Bacteria are found almost anywhere—in the water, soil, and atmosphere, as well as on our skin and in our mouths and large intestines. Although some bacteria cause diseases, others perform many services, both environmental and commercial. Bacteria are used to conduct genetic research in our laboratories, produce innumerable products in our factories, and help purify water in our sewage treatment plants.
Kingdoms
Taxonomists haven’t yet decided how to categorize archaea and bacteria into kingdoms. Domain Eukarya, on the other hand, has four kingdoms with which you may be familiar. Protists (kingdom Protista) range from unicellular to a few multicellular organisms (Fig. 1.7). Some are photosynthesizers, and others must ingest their food. Among the fungi (kingdom Fungi) are the familiar molds and mushrooms that, along with many types of bacteria, help decompose dead organisms (Fig. 1.8). Plants (kingdom Plantae) are well known as multicellular photosynthesizers (Fig. 1.9). -Animals (kingdom Animalia) are multicellular organisms that ingest their food (Fig. 1.10).
Scientific Naming
Biologists give each living thing a two-part scientific name called a binomial name. For example, the scientific name for the garden pea is Pisum sativum. The first word is the genus, and the second word is the -specific epithet of a species within a genus. The genus may be abbreviated (e.g., P. sativum). Scientific names are universally used by biologists to avoid confusion. Common names tend to overlap, and often they are in the language of the people who use that particular name. But scientific names are based on Latin, a universal language that not too long ago was well known by most scholars.
Biodiversity
Classifying organisms helps keep track of biodiversity because biologists classify all known species. Even so, biodiversity not only includes the total number of species, but also the variability of organisms’ genes and the variability of ecosystems in the bio-sphere.
The present number of species has been estimated to be as high as 15 million, but so far, under 2 million have been identified, named, and classified. Extinction is the death of a species or a larger taxonomic group. It is estimated that presently as many as 400 species per day are lost because of human activities. For example, several species of fishes have all but disappeared from the coral reefs of Indonesia and along the African coast because of overfishing. Many biologists are alarmed about the present rate of extinction and believe it may eventually rival the rates of the five mass extinctions that have occurred during our planet’s history. The dino-saurs -became extinct during the last mass extinction, 65 million years ago.
It has been suggested that the primary bioethical issue of our time is preservation of ecosystems, because in that way we preserve biodiversity. Just as a native fisherman who assists in overfishing a reef is doing away with his own food source, we as a society are contributing to the destruction of our home, the bio-sphere, when we destroy ecosystems. If instead we adopt a conservation ethic that preserves ecosystems, we are helping to ensure the continued existence of all species, including our own.
1.4		Science As a Way of Knowing
Biology, with its numerous branches, is the scientific study of life (Fig. 1.11). Religion, aesthetics, ethics, and science are all ways that human beings have of finding order in the natural world. Science differs from the other fields by its process, which often involves the use of the scientific method (Fig. 1.12).
Observation
The scientific method begins with observations. We can observe with our noses that dinner is almost ready, observe with our fingertips that a surface is smooth and cold, and observe with our ears that a piano needs tuning. Scientists also extend the ability of their senses by using instruments; for example, the microscope enables them to see objects that could never be seen by the naked eye. Finally, 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. 
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. While examining a petri dish containing the mold Penicillium, Alexander Fleming observed an area around the mold that was free of bacteria. Fleming thought the mold might be producing an antibacterial substance. We call such a possible explanation for a natural event a hypothesis. Fleming’s hypothesis was supported by further study.
All of a scientist’s past experiences, no matter what they might be, may influence the formation of a hypothesis. But a scientist only considers hypotheses that can be tested by experiments or further observations. Moral and religious beliefs, while very important to our lives, differ between cultures and through time, and are not always testable.
Experiments/Further Observations
The manner in which a scientist intends to conduct an experiment is called the experimental design. A good experimental design ensures that scientists are testing what they want to test and that their results will be meaningful. When an experiment is done in a laboratory, all conditions can be kept constant except for an experimental variable, which is deliberately changed. One or more test groups are exposed to the experimental variable, but one other group, called the control group, is not. If, by chance, the control group shows the same results as the test group, the experimenter knows the results are invalid. 
Scientists often use a model, a representation of an -actual object. Modeling occurs when scientists use software to decide how human activities will affect climate, or when they use mice instead of humans for, say, testing a new drug. Ideally, a medicine that is effective in mice should still be tested in humans. Whenever a model is used to study a phenomenon, any conclusion is in need of further testing. Someday, a scientist might devise a way to test the conclusion further.
Data
The results of an experiment are referred to as the data. Mathematical data are often displayed in the form of a graph or table. Sometimes studies rely on statistical data. Let’s say an investigator wants to know if eating onions can prevent women from getting osteoporosis (weak bones). The scientist conducts a survey asking women about their onion-eating habits and then correlates these data with the condition of their bones. Other scientists critiquing this study would want to know: How many women were surveyed? How old were the women? What were their exercise habits? What criteria were used to determine the condition of their bones? And what is the probability that the data are in error? The greater the variance in the data, the greater the probability of error. In any case, even if the data do suggest a correlation, scientists would want to know the ingredient in onions that has a direct biochemical or physiological effect on bones. In this way scientists are skeptics who always pressure one another to keep investigating.
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 hypothesis for another experiment (Fig. 1.12). 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. -Experiments and observations must be repeatable—that is, the reporting scientist and any scientist who repeats the experiment must get the same results, or else the data are suspect.
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 dictates the form, function, and behavior of organisms; and the theory of evolution, which says that all organisms have a common ancestor, and each one is adapted to a particular way of life. 
The theory of evolution is considered the unifying concept of biology because it pertains to many different aspects of organisms. 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 that 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 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. 
Example of a Controlled Study
Some investigators were concerned about the excessive use of nitrogen fertilizer to grow crops. Water pollution occurs when rain runoff washes fertilizer into nearby bodies of water. Nitrogen from a fertilizer can make well water on farms toxic to drink, especially for infants. 
The investigators hypothesized that if pea plants were grown and turned over in the soil before winter wheat was planted there, they would act as a “natural fertilizer,” eliminating the need to add nitrogen fertilizer. If so, wheat could be grown successfully in an environmentally friendly way. 
The Study
In this study, the investigators decided on the following experimental design:
Control Group
Winter wheat was planted in pots of soil that received no prior treatment. 
Test Groups
	1.	Winter wheat was grown in clay pots in soil treated with an inorganic nitrogen fertilizer (45 kg/ha).
	2.	Winter wheat was grown in clay pots in soil treated with twice as much nitrogen fertilizer (90 kg/ha). 
	3.	Pea plants were grown in clay pots (Fig. 1.13a). The pea plants were then turned over into the soil, and winter wheat was planted in the same pots (Fig. 1.13b).
To ensure a controlled experiment, the conditions for the control group and the test groups were identical; the plants were exposed to the same environmental conditions and watered equally (Fig. 1.13c). During the following spring, the wheat plants were dried and weighed to determine the wheat yield in each of the pots.
The ResultsAfter the first year, the wheat yield for test groups 1 and 2 was greater than for the control group (Fig. 1.13d). To the surprise of investigators, wheat production following summer planting of peas did not demonstrate as high a yield as even the control group (aqua bar compared to gray bar.) 
Conclusion:The hypothesis is not supported. Wheat yield following the growth of peas is not as high as the yield following the use of nitrogen fertilizer at the end of year 1.
Continuing the Experiment
The researchers decided to continue the experiment using the same design and the same pots as before, to see if the buildup of residual soil nitrogen from pea plants would eventually increase the yield of wheat. Figure 1.13d shows the results after year 2: The wheat yield following the growth of peas (aqua bar) is better than that for the other groups.
Conclusion: The hypothesis is supported. At the end of two years, the summer planting of peas prior to the planting of wheat does result in a higher wheat yield.
The researchers continued their experiment for still another year. After year 3, the wheat yield had decreased in both the control group and the inorganic nitrogen fertilizer groups, while the wheat yield following the planting of peas was dramatically better (aqua bar compared to the other bars in year 3, Fig. 1.13d). 
The researchers suggested that their results showed that the soil had gradually improved after the planting of the peas. The researchers published their results in a -scientific journal1 because any alternative to the use of nitrogen fertilizer would be beneficial to our society, which depends on wheat as a staple food. Also, a regimen that improves rather than depletes the soil would enable agriculture to continue unabated in the future. 
1.5		Science and Society
Many scientists work in the field or the laboratory collecting data and coming to conclusions that sometimes seem remote from our everyday lives. Other scientists are interested in using the findings of past and present scientists to produce a product or develop a technique that does affect our lives. The application of scientific knowledge for a practical purpose is called technology. For example, virology, the study of viruses and their molecular chemistry, led to the discovery of new drugs that extend the life-spans of people who have AIDS. And cell biology research discovers the causes of cancer, allowing physicians to develop various cancer treatments. 
Most technologies have benefits but also drawbacks. Research has led to modern agricultural practices that are helping to feed the burgeoning world population. However, the use of nitrogen fertilizers leads to water pollution, and the use of pesticides, as you may know, kills not only pests but also other types of organisms. The scientist Rachel Carson wrote the book Silent Spring to make the public aware of the harmful environmental effects of pesticide use. 
Who should decide how, and even whether, a technology is put to use? Making value judgments is not a part of science. Ethical and moral decisions must be made by all people. Therefore, the responsibility for how to use the fruits of science must reside with people from all walks of life, and not with scientists alone. Scientists should provide the public with as much information as possible, but all citizens, including scientists, should make decisions about the use of technologies.
In the future we may need to decide whether we want to stop producing bioengineered organisms if they prove to be harmful to the environment. Also, through gene therapy, we are developing the ability to cure diseases and to alter the genes of our offspring. Perhaps one day we might even be able to clone ourselves. Should we do these things? So far, as a society, we continue to believe in the sacredness of human life, and therefore we have passed laws against doing research with fetal tissues or using fetal tissues to cure human ills. Even if the procedure for human cloning is perfected, we may also continue to rule against its use. Each of us must wrestle with this and other bioethical issues, and make decisions that we hope are beneficial to society.
The Chapter In Review
Summary
1.1		The Unity and Diversity of Life
Living things, often called organisms, share several common characteristics. Organisms
	•	are organized (have levels of organization).
	•	acquire materials and energy.
	•	respond to external stimuli.
	•	reproduce and develop.
	•	have adaptations.
Evolution explains the unity and diversity of life. Descent from a common ancestor explains why organisms share some characteristics, and adaptation to various ways of life explains the diversity of life-forms. 
1.2		How the Biosphere Is Organized
Populations within a community interact with one another and with the physical environment, forming an ecosystem. With an ecosystem, nutrients cycle, but energy flows unidirectionally and eventually becomes heat.
1.3		How Organisms Are Classified
According to the rules of taxonomy, species belong to the following categories (from the most inclusive to the least inclusive):
Domains
	•	Archaea: prokaryotes
	•	Bacteria: prokaryotes
	•	Eukarya: eukaryotes
Kingdoms in domain Eukarya:
	•	Protista: unicellular to multicellular organisms with various modes of nutrition
	•	Fungi: live on debris; molds and mushrooms
	•	Plantae: multicellular photosynthesizers
	•	Animalia: multicellular organisms that ingest food
To classify a particular organism, scientists use a consistent sequence of categories. A binomial name consists of the genus and the specific epithet. For example, here is how the names Homo sapiens and Zea mays are derived:
1.4		Science As a Way of Knowing
The scientific process includes a series of systemic steps known as the scientific method: 
	•	Observations, which use the senses and may also include studies done by others
	•	A hypothesis (a statement to be tested)
	•	New observations and experiments
	•	A conclusion reached by analyzing data to determine whether the results support or do not support the hypothesis.
A hypothesis confirmed by many different studies becomes known as a theory. Examples are the cell theory, the gene theory, and the theory of evolution, which is the unifying concept of biology. 
1.5		Science and Society
Scientific findings often lead to the development of a technology that can be of service to human beings. Technologies have both benefits and drawbacks. Every member of society needs to be prepared to participate in deciding whether, and how, a technology should be used. 
Thinking Scientifically
	1.	While shopping for fertilizer for the tomato plants in your garden, you have a choice between a name-brand and a generic brand. The labels indicate that they are identical in composition, but the advertising for the name-brand fertilizer claims that it is superior to all other fertilizers. How would you set up an experiment to test that claim?
	2.	Two peach varieties (Biscoe and Encore) were treated with a plant growth regulator that influences fruit softening. The three treatment application dates were 21, 14, and 7 days before harvest. Which variety showed effects that increased consistently from 21 to 7 days before harvest? Did the growth regulator work equally effectively in both cultivars? Which treatment was most effective?  
Testing Yourself
Choose the best answer for each question.
	1.	The smallest living unit is a(n)
	a. atom.	c. cell.
	b. molecule.	d. tissue.
	2.	In the following diagram, label the levels of biological organization: 
	3.	All of the chemical reactions that occur in a cell are called
	a. homeostasis.	c. heterostasis.
	b. metabolism.	d. cytoplasm. 
	4.	The process of turning solar energy into chemical energy is called
	a. work.	c. photosynthesis.
	b. metabolism.	d. respiration.
For questions 5-–9, choose one answer from the following key.
Key:
		a. unicellular organism
b. multicellular organism
c. neither
d. both
	5.	Capable of responding to the environment. 
	6.	Reproduces by uniting an egg with a sperm.
	7.	Contains tissues.  
	8.	Contains genes. 
	9.	Creates energy. 
	10.	In an ecosystem,
	a. energy flows and nutrients cycle.
	b. energy cycles and nutrients flow.
	c. energy and nutrients flow.
	d. energy and nutrients cycle.
	11.	Taxonomy is a biological discipline in which organisms are grouped according to their
	a. geographic location.	c. common ancestries.
	b. size.	d. gene number.
	12.	The first cells to evolve in the primitive Earth were most likely members of the domain
	a. Archaea.
	b. Bacteria.
	c. Eukarya.
	13.	Choose the correct way to represent the scientific name of corn.
	a. Zea Mays	e. Zea Mays
	b. zea mays	f. zea mays
	c. Zea mays	g. Zea mays
	d. zea Mays	h. zea Mays
Go to www.mhhe.com/maderessentials for more quiz questions.
Bioethical Issue
Clinical trials on drug efficacy are typically carried out on two groups of patients. One group receives the drug, while the other (the control group) receives a placebo. The control group determines the extent to which psychology affects people who believe they are taking the new drug. 
Suppose a new cancer drug has been developed. Many people sign up to participate in a clinical trial to test the drug’s ability to slow the progression of the disease. These people know that they may receive a placebo in place of the real drug, but they participate because they have run out of options. Is it right to give the placebo to some of the participants, knowing that their disease is going to progress during the course of the trial? What if the drug was one that alleviated pain in chronic pain sufferers? In this case, no disease progression would occur during the course of the trial, but participants taking the placebo would have to contend with serious pain.
Understanding the Terms
adaptation4
animal6
binomial name7
biodiversity7
biology8
biosphere5
cell2
class6
community5
conclusion9
control group8
data9
domain6
domain Archaea6
domain Bacteria6
domain Eukarya6
ecosystem5
energy3
evolution4
experimental design8
experimental variable8
extinction7
family6
fungus6
gene4
genus6
homeostasis3
hypothesis8
inductive reasoning8
kingdom6
metabolism3
model8
multicellular2
natural selection4
observation8
order6
organ2
organism2
organ system2
photosynthesis3
phylum6
plant6
population5
principle9
protist6
reproduce3
scientific theory9
species4, 6
taxonomy6
tissue2
unicellular2
Match the terms to these definitions:
a.	_______________	A scientist’s suggested explanation for a 
natural event. 
b.	_______________	A representation of a natural phenomenon studied by scientists when the real object is impossible to study. 
c.	_______________	A modification that helps equip organisms for their way of life.
d.	_______________	A group of interbreeding individuals. 
e.	_______________	The discipline of classifying organisms according to certain rules.
f.	_______________	The region of the Earth’s surface where all organisms are found.
g.	_______________	Information collected from a scientific experiment. 
A single teaspoon of soil may contain up to 1 billion microorganisms, each with the characteristics of life.
Only 2 million of the estimated 15 million species have been identified. Most unidentified species live in tropical rain forests.
The number of bacteria on your skin is roughly equal to the number of humans on Earth.
Figure 1.1Levels of biological organization.
Figure 1.2Acquiring nutrient materials and energy.
a. Osprey, a type of hawk, eating a fish. b. Humans harvesting crops.
Figure 1.3 A human family.
Whether they are unicellular or multicellular, all organisms reproduce. Offspring receive a copy of their parents’ DNA and therefore a copy of their genes.
Figure 1.4 A grassland, a terrestrial ecosystem.

In an ecosystem, chemical cycling (blue arrows) and energy ﬂow begin when plants use solar energy and inorganic nutrients to produce their own food (organic nutrients). Chemicals and energy are passed from one population to another in a food chain. Eventually, energy dissipates as heat (red arrows). With the death and decomposition of organisms, inorganic nutrients are returned to living plants once more. 
Figure 1.5Domain Archaea.
Archaea are capable of living in extreme environments. These are exterior and interior views of Methanosarcina mazei.
Figure 1.6Domain Bacteria.
Bacteria are structurally simple but metabolically diverse. These are exterior and interior views of Escherichia coli.
Figure 1.7Domain Eukarya, Kingdom Protista.
Many protists are unicellular. This is Euglena.
Figure 1.8Domain Eukarya, Kingdom Fungi.
Fungi are multicellular and break down organic debris. This is a shaggy mane mushroom.
Figure 1.9Domain Eukarya, Kingdom Plantae.
Plants are multicellular photosynthesizers. This is a rose.
Figure 1.10Domain Eukarya, Kingdom Animalia.
Animals are multicellular and ingest their food. This is a European lynx.
Figure 1.11Biologists.
Biologists work in a variety of settings. For example, (a) some botanists work in greenhouses; (b) some biologists, such as this biochemist, work in laboratories; and  (c) many ecologists and environmentalists collect data in the field.
Figure 1.12Flow diagram for the scientific method.
On the basis of new and/or previous observations, a scientist formulates a hypothesis. The hypothesis is 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.
Figure 1.13A controlled study.
a. Pea plants growing in clay pots at the end of the summer. b. After the pea plants were mixed into the soil, winter wheat was planted in the same pots.
Figure 1.13A controlled study, continued.
c. Winter wheat was grown in both control and test pots. d. Three years of data are given in this bar graph.
1 Bidlack, J. E., Rao, S. C., and Demezas, D. H. 2001. Nodulation, nitrogenase activity, and dry weight of chickpea and pigeon pea cultivars using different Bradyrhizobium strains. Journal of Plant Nutrition 24:549–60.

levels of classification
Category	Human	Corn
Domain	Eukarya	Eukarya
Kingdom	Animalia	Plantae
Phylum	Chordata	Anthophyta
Class	Mammalia	Liliopsida
Order	Primates	Commelinales

Family	Hominidae	Poaceae
Genus	Homo	Zea
Species*	H. sapiens	Z. mays
* To specify an organism, you must use the full binomial name, such as Homo sapiens.

Check Your Progress
	1.	List the levels of organization of a multicellular animal, beginning with molecules.
	2.	 List five features common to organisms.
	3.	Define evolution.
Answers: 1. molecules-cells-tissues-organs-organ systems-organism 2. Organisms are organized, acquire materials and energy, respond to external stimuli, reproduce and develop, and have adaptations.3. Evolution is descent of species from common ancestors, with genetic modifications that make each species more suited to its environment.
Check Your Progress
		Contrast a community with an ecosystem.
Answer: A community consists of different populations that interact in a particular place. An ecosystem is a community together with the physical environment with which it interacts.
Check Your Progress
	1.	List the eight classification categories, from least to most inclusive.
	2.	Explain why scientists prefer to refer to organisms by their scientific names rather than their common name.
	3.	List the four kingdoms in domain Eukarya.
Answers:1. species, genus, family, order, class, phylum, kingdom, domain. 2. For various reasons, the same organism can have different common names, or the same common name may be given to several different organisms. Each organism has only one scientific name, and that name is never used for any other organism.3. Protista, Fungi, Plantae, Animalia.
Check Your Progress
	1.	Explain how a scientist uses the scientific method to create a hypothesis.
	2.	Compare and contrast the control group with the test groups in a scientific study.
Answers:1. First, a scientist makes observations about some phenomenon in the natural world. Then, s/he uses inductive reasoning to formulate a hypothesis, a possible explanation for the phenomenon. Finally, s/he uses the information gained to create an explanation for the phenomenon.2. In an experiment, the control group is not exposed to the experimental variable, but the test groups are exposed to the experimental variable. Otherwise, if the control groups and the test groups were exposed to identical conditions, there would be no basis for comparing the results.