1.0 Biology; Biology and Scientific Methods

Quantitative Data

data that represents a quantity; numeric data

Qualitative Data

data that represents qualities or characteristics that can't be expressed by a number

photosynthesis

the process by which plants and certain other organisms use the energy of sunlight to convert carbon dioxide and water into sugar and oxygen

Cellular respiration

the process of breaking down glucose for the production of ATP in the presence of oxygen

Metabolism

the total of all chemical reactions within an organism

Scientists follow a variety of methods to answer questions about the natural world.

While there is no single recipe to follow in a scientific investigation, scientists rely on a number of common approaches to observe and question the natural world. In testing those questions, scientists provide many answers—and often raise even more questions to investigate.

1.02 Biology and Scientific Methods Scientists follow a variety of methods to answer questions about the natural world. The Scientific Method makes observations and asks questions, forms a hypothesis, performs an experiment, gathers and analyzes data, draws conclusions, and communicates. If, after drawing conclusions, the hypothesis is wrong, the scientific method wants us to alter the hypothesis/form a new hypothesis and perform the experiment again.

Why do leaves change color in the fall? Can crops be made more insect resistant and cars more fuel efficient? In this lesson, you'll learn how scientific methods help us identify and answer questions about the world we live in.

The sun is the main source of energy for most living things. Most life on earth depends on the sun's energy.

Can you imagine a distance of 150 million km? How long might it take to travel that far? Earth's circumference is a mere 13,000 km. The fact is that your very life, along with more than 99 percent of all living things on earth, depends on energy that travels 150 million km each second of each day. That energy travels from the sun. Not only does the sun's energy travel that immense distance, but it also takes different forms. It lights up the planet. It provides heat. Plants use it to make food.

Organelle

a differentiated structure within a cell, such as a mitochondrion, vacuole, or chloroplast, that performs a specific function

Tissue

a group of cells that are similar in structure and that work together to perform a certain function

Organ

a group of different tissues that work together to perform a specific function

Biome

a large area dominated by characteristic plants and animals, such as a rain forest, desert, or tundra

experiment

a set of organized steps that scientists follow under controlled conditions to test a theory or hypothesis

homeostasis

a state of balance reached through reactions within a cell or organism

Most of what we know about the natural world comes from the application of scientific methods.

Nearly everything you'll learn in this biology course was discovered through scientific methods. The first steps of a scientific method—making observations and asking questions, developing hypotheses, and designing experiments—are the groundwork for a successful investigation.

Organisms take in energy from their environment and use it to grow, reproduce, and maintain structure.

he stone plant grows in African deserts. If you came across a stone plant, your first impression might be that it was just a pile of pebble. If you were to wait long enough, however, the plant would eventually produce a flower—a reproductive structure that gives you a clue that it is actually a living organism and not a rock. Explore two phases of the plant's life cycle. Stone Plants (Here is a picture: http://davesgarden.com/guides/pf/showimage/64887/ ) Like all living things, stone plants require energy to maintain their existing structures, such as leaves, to build new structures, such as flowers, to grow, and to reproduce. That energy comes from the environment. In fact, living things meet the challenges of getting and using energy as one of the primary activities of life.

Variable

in an experiment, a factor that is unknown or can change

Control Group

in an experiment, a group that a scientist can compare to another group that is identical except for one property or factor

Independent Variable

in an experiment, the factor that a scientist deliberately manipulates

Dependent Variable

in an experiment, the variable that depends on the other variables

1.10 Structure and Function The structure of an organism's parts relates to the function of the parts. The structure of an organism's parts depends on the function of those parts.

Can you imagine a bicycle with square tires or a suitcase with no handle? Those objects are designed for a purpose, so they have a special structure. Tires are round, for example, because round is the best shape for the job. A similar relationship exists between the structure of an organism's parts and the function of those parts.

The parts of a scientific method work together in a cycle.

The final steps of an experimental scientific method—gathering and analyzing data, drawing conclusions, communicating results, and refining hypotheses—are all important steps in advancing the field of biology. Combined with the first steps, a scientific method operates as a cycle: By drawing conclusions about one study, scientists often think of new questions to investigate.

Multicell organisms have levels of organization.

A key principle of life is that internally multicell organisms are organized in levels. These levels are the cell, tissue, organ, and organ system. Many specialized cells make up a tissue. The body contains four basic types of tissue, each made of a specific, specialized cell type: Epithelial tissues are cells that cover body surfaces. Connective tissues support and strengthen other tissues. Muscle tissues cause the body to move. Nerve tissues run through the other three, receiving and processing information.

adenosine triphosphate (ATP)

ATP; the molecule that delivers usable chemical energy for almost all processes and reactions that a cell must undergo to survive

Communities and ecosystems include different types of organisms that interact with one another.

A coral reef, a river's edge in a tropical rain forest, or a water hole in a prairie might not look very organized, but ecologists studying these and other ecosystems look for and identify patterns that explain how the parts of these ecosystems fit together and function as a whole. Any ecosystem is made of a group of communities. A community is a group of species that interact and live in the same place. Those communities are made up of populations —groups of individuals of the same species. A biome is a larger geographic area containing several ecosystems and dominated by specific kinds of animals and plants. This reef ecosystem is made up of communities of many different species: fish, coral, algae, and others.

Tooth structure relates to function. A shark uses its teeth to tear flesh. A walrus uses its long tusks to pull itself over ice. A zebra uses its teeth to grind up tough plants. Humans use their teeth for both tearing and grinding. Tongue Adaptations: Tongues have a variety of shapes and structures, too. A snake's forked tongue has sensory nerves that capture chemicals from the air and help the snake smell what's around it. The backward-facing spikes on a penguin's tongue help push slippery fish down the penguin's throat. A chameleon's long tongue can flick out and capture insects from a distance.

A shark's multiple rows of pointed, serrated teeth are sharp as razors. Those teeth are made for one thing only—to tear flesh. A walrus's massive canine teeth, called tusks, are long and pointed. Walruses use their tusks for defending themselves and pulling themselves across the ice. Think about the flat teeth of a gazelle or zebra. Why do they have that shape? The teeth of plant-eating animals are shaped to grind up tough plant fibers. As for humans, we eat meat and plants, and we have both flat and pointed teeth. In fact, you can guess what kind of food an animal eats simply by looking at the structure of its teeth.

Observations of the natural world lead to questions. The long straming tail feathers on the barn swallow mark it as a male. The female does not have these extra long side feathers on its tail. Barn Swallows Barn swallows live in temperate zones all across the world, from North America to northern Europe, Asia, and Africa. They live in open areas like agricultural zones, and they nest in barns, under the eaves of houses, and even in caves.

A team of Swedish scientists observed that male barn swallows have significantly longer tails than female barn swallows, so they raised a question: Does the length of a male's tail influence a female's choice of mate? This simple observation and the subsequent question led Anders Møller and his team to design a series of experiments on barn swallows' tail length. Those scientists eventually found answers to the tail-length question and many other questions along the way. Their work has played an important role in our understanding of the significance of ornamentation among animals. Explore the difference in tail length between female and male barn swallows: Barn Swallow Tails

Scientists draw conclusions based on their data. The Scientific Process: Make Observations and Ask Questions Form Hypotheses Perform Experiments Gather and Analyze Data Draw Conclusions Communicate Alter Hypotheses/Form New Hypotheses

All that time spent conducting experiments should lead somewhere, right? Most of the time, scientists are able to look at the data they collected during an experiment and draw conclusions from it. Sometimes, however, scientists have no choice but to conclude that they haven't answered their question. They might need to collect more data, restate their hypothesis, or design a different experiment. Usually science moves forward in a series of small steps, with each step generating just as many questions as answers. Science rarely progresses as a series of major groundbreaking discoveries, one after another. Perhaps a newly discovered gene is found in people who develop cancer, but that's not enough information to conclude that it causes cancer. Or maybe a new drug only clears up pimples in girls, but it doesn't work in boys. Turn to page 10 in your reference book for an overview of scientific methods.

A hypothesis is often based on an "if-then" statement. Behavioral ecologists, scientists who study animal interactions, might measure the number of offspring in this nest to determine an individual spider's breeding success.

An "if-then" statement provides a handy setup for experimental testing. One possible hypothesis for the barn swallows' tail length could be, "If a male has long tail feathers, then he is likely to have more offspring than a male with short tail feathers." An "if-then" statement identifies the variable of interest in a study (tail length) and also identifies what kind of data to collect (number of offspring). For this study, you would collect data on the number of offspring a male has to test the effects of changing the variable—tail length.

Organisms respond to their environments.

Another characteristic of life is response to the environment. Why do you think response is important to living organisms? Think about what you just learned about homeostasis. If the environment changes dramatically, it might become difficult for an organism to maintain homeostasis, even if its internal systems are working properly. For example, hundreds of species of songbirds migrate south every winter. Why do they do this? One reason is that their food supply disappears in the winter. Many songbirds feed on insects, many of which enter a state similar to hibernation in the fall. Hidden deep away in burrows, they're just not available for birds to eat. Birds respond by migrating to warmer climates where insects are still available as food. Summer tanagers have adapted to catch bees and wipe them on a branch to remove their stingers.

Organization is a key principle in the study of life. From cells to entire organisms, the components of living things are organized to function as a unit.

At the most basic level, many of the questions biologists ask have to do with organization: How are the components of living things put together, and how do those components work together? Scientists ask: What is the function of a newly discovered gene? Where inside of a cell is energy produced? How do muscle cells power movement? How do the parts of an ecosystem fit together and function as a whole? Each question addresses an aspect of organization in the biological world. By understanding the principles of organization, biologists try to piece together a better understanding of the connections between living things and between the parts of any single living organism.

Organisms have evolutionary adaptations that help them survive and reproduce in their environment, which affects the ways they interact within populations, communities, ecosystems, and biomes.

Biological organization extends beyond the level of the organism to include populations, communities, ecosystems, and biomes. By understanding how organisms function within each level, scientists may explain how ecosystems function and predict the effects of disrupting ecosystems. Evolutionary adaptations help species survive and reproduce in a given environment, and populations of species evolve within a particular environmental context. The currency of that evolutionary change is DNA, the genetic material that is passed from parents to offspring.

Cellular respiration breaks down glucose into usable energy. Cellular Respiration Transcript: Positioned in the center of the space is the title, Cellular respiration. Under the title is a drawing of a bank. The bank has four windows, four pillars, and a large sign above the pillars. The sign says, Energy Bank. Moving toward the bank from the left edge of the space is a drawing of a check with the word glucose on it. The movement suggests that the check will be deposited in the bank. The check disappears in the bank. When that happens, the windows flash light and dark and light and dark several times. Then several green rectangles, which are stacked one on top of the other, emerge from the right side of the bank and move toward the right and out of the space. The green rectangles give the appearance of paper money. The letters A T P appear on the stack.

But glucose is not a direct source of energy. Glucose is stored chemical energy. It's something like money in the bank: It's there, but you have to go get it before you can spend it. Glucose is the fundamental molecule for yet another process that results in usable energy— cellular respiration. Cellular respiration breaks down glucose and releases energy. It transforms glucose into a form of energy that cells can use directly to fuel their various needs. The chemical energy that cells use is called adenosine triphosphate (ATP). You will learn much more about ATP in future lessons.

Changes in inherited characteristics over many generations lead to evolution. Every organism's genetic makeup is encoded in molecules of DNA that are passed on through the generations. Coevolution: Plants and Pollinators: Scientists suggest that many plants and pollinators have coevolved, meaning their traits have evolved together. For example, hummingbirds pollinate flowers that are red and waxy and have a deep throat. The shape of a hummingbird's beak helps it reach nectar deep within a flower.

DNA is the currency of heredity: It is the molecule that contains the genetic information passed from parents to offspring. In this way, you also can call DNA the currency of evolution. Changes in the characteristics inherited by all individuals in a population over a long period of time can lead the population to evolve.

Scientists develop hypotheses from their questions about the natural world. Ornamentation—flashy colors and extravagant displays—may serve several purposes including attraction of a mate.

If you were to ask the same question Møller and his team did about tail length in barn swallows, how might you investigate it experimentally? To begin, you'd restate the question as a hypothesis—a tentative explanation of an observed phenomenon. But on which information would you base your tentative explanation? By looking at research that other scientists have done with a variety of animals, you might learn that ornamentation—like bright colors, huge antlers, or a long tail—might increase a male's success at finding a mate and producing offspring. Knowing what others have learned about ornamentation among animals will help you form a working hypothesis about the importance of tail length among barn swallows.

Scientists refine their hypotheses and design new investigations. Follow up Studies: Follow-up studies showed that male barn swallows with long tails had fewer blood-sucking parasites on their bodies—and so did their offspring. But why would long tails and parasite resistance be correlated? Scientists still don't know, but perhaps someday, we'll find the answer.

Even after scientists have published a study, they still have more work to do. Often, new questions arise from a study's conclusions. For example, why would female barn swallows prefer to mate with males with long tails as opposed to short ones? What does a long tail indicate about a male? Møller and his colleagues asked that follow-up question and found some surprising results. This type of follow-up is an essential part of any scientific method: Studies frequently lead to new investigations and other questions. By communicating and questioning the conclusions of scientific investigations, the field of biology continues to move forward. A barn swallow flying in the sky: Although Moller and others have taught us much about the behavior of barn swallows and other animals, there is still much more to discover.

Living things meet the challenges of getting and using energy as one of the primary activities of life. It is probably obvious to you that strenuous activity such as rock climbing requires a lot of energy. Although you may be partially immobilized, a lot of energy is required to mend a broken ankle. When you're resting, or even fast asleep, your body requires energy for all of the processes of life.

Everything you do in an average day—from getting out of bed in the morning to reading the words on this computer screen—requires energy. Even when you are at rest, many chemical reactions are happening in your body. These chemical reactions make it possible for your body to use the energy in the food you eat for all the processes of life. Did you skin your knee while out biking? Your body uses energy to repair the wound. Are you still growing taller? Your body needs energy for growth, too. And even if you're not growing taller, your body still uses energy to maintain your bones, muscles, and skin. When you think about it, your body even needs energy to obtain energy. When you pick up a slice of pizza, your muscles use energy to move the pizza from the plate to your mouth. You use energy to chew. You even need energy to digest your meal.

Organization is one of the defining principles in biology.

From the level of the cell to the level of the ecosystem, biologists try to understand the rules that govern how organisms are put together and how organisms function together in the environment. By looking to the structure of the cell and the levels of organization in multicell organisms, scientists have begun to piece together some of the underlying principles of how life works.

Some organisms are made of only one cell, yet they still meet the challenges of life. Each individual Streptococcus bacteria cell is capable of carrying out all of the processes of life.

Have you ever had the infection strep throat? How about an ear infection? Illnesses like these and many others are caused by single-cell organisms called bacteria. A single bacterial cell is capable of growing, developing, reproducing, and responding to its environment. Bacterial cells also have a complex metabolism and maintain homeostasis. While they are too tiny to see with the naked eye, bacteria and other single-cell organisms are just as capable of carrying out all processes of life as you are.

Homeostasis involves regulating many different conditions in the body. Turkey Vulture A turkey vulture defecates on its own legs. By doing so in hot weather, this species not only removes wastes from its system, but also helps keep itself cool as the moisture evaporates, cooling blood in its legs.

Homeostasis is about a lot more than just maintaining body temperature. Organisms also require a balance of water, energy, and nutrients to stay alive. Different systems in the body, such as the excretory system, help maintain homeostasis by controlling the balance of water and minerals in the body, controlling metabolism, and getting rid of wastes. You might not even recognize the ways in which your body maintains homeostasis. When you eat, cells in your body produce wastes as they break down food molecules for energy. Your body must get rid of those wastes so that your cells remain functional. All living things need to establish and maintain homeostasis.

Disruption to part of an ecosystem can affect the whole ecosystem. When released in a U.S. pond, the voracious northern snakehead fish from Asia can quickly kill off all native fish. Introduced to Australia to devour pesty insects, cane toads are now a major pest since they eat everything, including small mammals. European starlings thrive in the United States, where they compete for nesting holes with several native species. Introduced to the United States, beautiful but aggressive mute swans compete fiercely with native trumpeter and tundra swans..

If one of the organs in your body stops functioning properly, your entire body may be affected. In much the same way, if a population in an ecosystem is changed in some way—increasing, decreasing, or disappearing—the effects may be felt throughout the entire ecosystem. For example, if a pollinator species—animals that help plants reproduce by carrying pollen from one flower to another—disappears from an ecosystem, some types of plants won't be able to reproduce. This, in turn, may remove an important food source for many animals in the ecosystem. Likewise, introducing a foreign species, such as those shown in the gallery at right, may upset an ecosystem's balance.

A well-designed experiment includes an experimental group and a control or baseline group. Well-Designed Experiments: Every field of science relies on experiments that are well designed. For example, the field of drug development relies on experiments with new medications. In these trials, scientists learn how effective a new medication is by comparing an experimental group of patients who receive a drug to a control group of patients who do not.

If you want to know how changing a variable like tail length affects an experiment's outcome, such as the number of offspring a male bird has, you need to compare the experimental group, in which the variable has been changed, to a baseline or control group, in which the variable is not changed. Does tail length affect the number of offspring that a male barn swallow has? Møller's team set up two experimental groups to answer this question: They glued long feathers to a normal bird's tail in one group, and clipped short a normal bird's tail feathers in the other. They also established two control groups of birds with normal-length tails.

An experiment includes variables that are tested, as well as variables that are kept constant.

In any experiment, you should always be sure that you are only testing the variable you want to test. You can ensure this by controlling your experiment. For example, if you wanted to know which of two fertilizers worked better for your tomato plants, you would give one group of plants fertilizer A and the other group fertilizer B. You also would establish a control group of plants that receive no fertilizer. You would keep all other growth conditions—amount of light, amount of water, and type of soil—the same. This way, you know that any differences you see in plant growth can be accounted for by the fertilizers alone. (Picture: Three plants in three pots marked as fertilizer A, fertilizer B, and No fertilizer and each having a light shining on them) To make sure you're testing only for the role of fertilizer in the experiment, light, water, and other conditions must remain constant.

Scientific methods have changed over time. An error in the preparation of a lab sample led Alexander Fleming to the discovery of the antibiotic penicillin. Aristotle's Philosophy: Aristotle observed that, where he lived, many species of birds seemed to disappear in the fall, only to reappear in the spring. Following his approach of natural philosophy, he reasoned that some species hibernate in hollow trees or even in the mud of wetlands during the cold season. When the weather warmed up, he reasoned, they aroused from their torpor to reappear. We now know that the coming and going of most birds is due to annual migrations.

In his study of wasps, Tinbergen followed a process that today we would recognize as a scientific method. But the Greek philosopher Aristotle, who lived thousands of years ago, would have approached Tinbergen's question very differently. One of the cornerstones of Aristotle's approach—which he called natural philosophy—was the idea that the human mind could find the answers to questions about the natural world based on reasoning alone. In Aristotle's time, experimentation was seen as unnatural. This idea prevailed until a period in the 1600s known as the Scientific Revolution, which focused on evidence obtained either through experiments or careful observations. The Scientific Revolution helped change how we approach the natural world. Turn to page 2 in your reference book for more details on how scientific thought and ideas have changed over time.

Scientists need to be sure that the manipulation itself doesn't affect the outcome of an experiment.

In the barn swallow study, what if the glue used to attach feathers smelled funny and kept females away? Then males with glued-on tails wouldn't mate, and you wouldn't learn anything about the impact of tail length on mating success. Møller and his team went an extra step to make sure that the very act of clipping or adding tail feathers didn't affect the results. They established two control groups. In one group, they left the tail feathers untouched. In the other group, they clipped the tail feathers but reattached them to the same bird with glue. By doing that, Møller's team could be sure that the manipulation itself didn't affect the outcome of the experiment.

Scientists plan what kind of data to gather when they design experiments. Moller and his team meticulously recorded the number of offspring in each barn swallow nest.

In the last lesson, you learned that Anders Møller and his team of Swedish scientists hypothesized, "If a male barn swallow has long tail feathers, then he is likely to have more offspring than a male with short tail feathers." To test their hypothesis, those scientists designed an experiment that included two experimental groups: normal birds that had their tails lengthened by gluing on extra feathers, and normal birds that had their tails clipped short. The experiment also included two control groups of birds with normal-length feathers. What kind of data would the scientists have needed to gather as the next part of their investigation? Look back to their hypothesis for clues. They expected that males with longer tails would have more offspring. To find out if their hypothesis was correct, they needed to gather data on each male barn swallow's number of offspring.

1.08 The Characteristics of Life 3 Organisms interact with one another to form more levels of biological organization: populations, communities, ecosystems, and biomes. Living organisms make up populations that make up communities that combine with nonliving things to make up ecosystems.

In the late 1960s, biologist Robert Paine found that the ochre sea star, which lives off the coast of Washington State, is a keystone species in its community. If it is removed, the distribution and abundance of all other organisms in its habitat change. This discovery is just one of many that helps us understand biological organization beyond the level of the organism.

Organisms sense, respond to, and interact with their environment.

In the late winter and early spring, temporary ponds called vernal pools form as snow melts in woodlands across the northeastern and midwestern United States. Mole salamanders sense and respond to these changes in their environment, and travel to the pools where, on rainy nights in the spring, they mate and lay eggs in the water. Responding to the environment is one of the basic characteristics of life. Response allows organisms to maintain homeostasis. In the case of the mole salamander, responding to the environment also makes possible another basic characteristic of life—reproduction.

Organ structure relates to function. Heart: Structure: The heart is a muscle with four chambers. Function: The heart pumps blood through your body. Lungs: Structure: Lungs are large and spongy. Function:Lungs take in and release air. Stomach: Structure: The stomach is a large sac lined with acid-resistant tissue. Function:The stomach contains acids that break down food into smaller particles.

Let's look at some of the different organs in the human body. How does the structure of each organ relate to its function?

The dependent variable is the variable that is measured in an experiment. Transcript from Video: With Fertilizer and Without Fertilizer Positioned in the center of the space side by side are two pots of soil. Positioned above each pot is a floodlight that shines down on the pot. Both pots have a stake with a sign. The sign on the stake in the left pot is, Fertilizer. The sign on the stake in the right pot is, No Fertilizer. Each pot contains the first shoot of a seedling. The shoots have an inverted U shape. The tops have not yet emerged from the soil. The shoot on the left is little bit larger than the shoot on the right. Positioned vertically in the far right of the space is a centimeter ruler. As time passes, the seedlings pop out of the soil and grow their first leaf. At that point, the seedling on the right is two centimeters tall. The seedling on the left is three centimeters tall. The seedlings grow a second leaf. At that point, the seedling on the right is about two and a half centimeters tall. The seedling on the left is about three and a half centimeters tall. The two leaves on each plant open. The leaves on the plant in the left pot are larger than the leaves on the plant in the right pot. The stems of the plants grow taller and two more leaves begin to sprout on each plant. At this time, the plant in the pot on the right is about three and a half centimeters tall. The plant in the pot on the left is about four and a half centimeters tall. By the time the second pairs of leaves are full grown, the plant in the pot on the right is about five and a half centimeters tall. The plant in the pot on the left is about seven and a half centimeters tall. At that point, the plant in the pot on the right stops growing. The plant in the pot on the left continues to grow until it is about nine and half centimeters tall and has two more leaves for a total of six leaves. This demonstration illustrates the effect of fertilizer on plant growth.

In the sunflower example, you would have manipulated growing conditions to see how changes in growing conditions affect plant height. You would have gathered data on plant height to see if plant height changes with respect to the amount of fertilizer the plant received. In the experiment, you could say that you are investigating how plant height depends on the amount of fertilizer. In other words, plant height is the dependent variable. You did not manipulate plant height yourself—it came about as a result of changes in the independent variable, the amount of fertilizer.

The independent variable is the variable that is manipulated in an experiment. The picture shows two potted plants, one with fertilizer and one with no fertilizer: At the beginning of the experiment, with all other factors being equal, the manipulation of the amount of fertilizer makes it the independent variable.

It seems as though there are a lot of variables to keep track of in an experiment, doesn't it? It is important that you understand them, because when the time comes to analyze your data, you need to be sure you know which variable is which. The independent variable in any experiment is always the factor that you actively change or manipulate. For example, assume you wanted to know how much fertilizer makes sunflowers grow taller. You would manipulate the amount of fertilizer, making it the independent variable.

Energy can flow through many organisms. The sun is the main source of energy for most organisms.

Let's see how all of this information fits together. Every organism is composed of cells. Your body alone contains trillions of cells, all working to keep you alive and growing. Cells need energy to do their jobs. Nearly all of the energy that living things use can be traced back to the sun. Some living things convert the energy of sunlight into chemical energy in the form of glucose. From there, the energy moves through other organisms. For example, a raspberry bush captures energy from the sun. A field mouse eats the raspberries and a caterpillar feeds on the bush's leaves. An owl eats the mouse and a toad eats the caterpillar. In this way, the sun's energy cycles through every living thing on the planet.

Living things convert energy from one form to another. Countless, constant chemical reactions taking place in your body allow you to do all the wonderful things you do.

Living organisms, from the tiniest bacterium to the tallest redwood, are like chemical factories. Countless chemical reactions occur inside the bodies of living organisms every minute of every day. These reactions involve processes for capturing the sun's energy, processing the chemical energy of food, building molecules, breaking down molecules, and shuttling molecules and other substances from one place to another. The total of all these chemical reactions is metabolism. Metabolism involves building things up, as well as breaking things down. You can think of metabolism as all the processes that break down raw materials, such as the food you eat, and build up all the chemicals your cells can use. Turn to page 16 in your reference book to learn more about the characteristics of life.

Living things require energy for all life functions. Every action requires energy.

Look around you. Your computer, cell phone, desk, and even the clothes you're wearing—at some point someone had to purchase all of those things with money. People spend money on objects and on services like a haircut or a car wash. Other living organisms have to spend, too, but they spend energy instead of money. Every single action a living thing does requires energy. A giant manta ray flapping its wings, a spider weaving a web, a cheetah breathing in hot African air—all actions, external and internal, are fueled by energy. But where does all of that energy come from?

Adaptations help organisms survive and reproduce in a given environment. In spring, often with snow still on the ground, salamanders come out of hibernation and seek a vernal pool. The female salamander lays several masses of 7 to 40 eggs about 6 in. below the water surface. The larval form of salamander has legs and the body shape of the adult, but with tail fins along the body and prominent external gills. When they first leave the water, juvenile salamanders retain signs of their gills for awhile. Two years after emerging, adult salamanders are ready to repeat the breeding cycle.

Mole salamanders have adaptive mating behaviors that allow them to reproduce in their environment. Adult salamanders live in leaf litter in the forest, but travel to vernal ponds to mate and lay eggs in the water. This is an evolutionary adaptation, a characteristic or behavior that is inherited or passed from parents to their offspring. Organisms with characteristics and behaviors that help them survive in their environment are more likely to reproduce and pass those characteristics to their offspring than organisms without those traits. This process, one concept in the theory of evolution, is known as natural selection.

Organisms take in light or chemical energy from their environment and use it to grow, reproduce, and maintain structure. Plants absorb energy from sunlight and convert it to chemical energy to produce food compounds. Plant-eating animals convert the plant food into chemical energy to power their own activities. The original light energy is again passed on as chemical energy when predators devour plant eaters. Life in the Dark: Hydrothermal Vent: Some locations on the ocean floor are home to organisms that never see the light of day. They obtain their energy not from the sun but from chemical compounds that seep through the ocean floor from deep within the earth.

Most of life on earth gets its energy, in one way or another, from the sun. And remember, energy comes in different forms. Plants, algae, and a few other organisms have structures that allow them to capture light energy. They convert this light energy, along with carbon dioxide and water, into chemical energy to drive reactions that produce complex molecules such as sugars, which provide chemical energy when broken down. When animals eat plants, they eat those food molecules. And when animals eat other animals that have eaten plants, they obtain chemical energy that originated with the sun's energy. Next time you eat a meal, think about the chemical energy in the food you're eating.

You can see the relationship between structure and function in types of cells. Red Blood Cells: Structure: Red blood cells are shaped like smooth discs. Function: Blood flows smoothly through arteries and veins. Skin Cells: Structure: Skin cells are shaped like plates of armor. Function: Skin covers and protects everything under its surface. Nerve Cells: Structure: Nerve cells are long and have armlike extensions. Function: Nerves pick up and send information. Fat Cells: Structure: Fat cells are expandable. Function: Fat stores energy that the body can use later. Muscle Cells: Structure: Muscle protein cells are elongated and can interlock. Function: Muscles contract and relax to move your body.

Not only are you made up entirely of cells, but your cells have different structures. How does the structure of a cell relate to its function?

Data can be quantitative or qualitative.

Numeric data—number of eggs or height of a plant—is called quantitative data. This kind of data represents a quantity of some variable, such as eggs, chicks, or plant height. Not all investigations will produce quantitative data. Some data is qualitative data: It represents qualities or characteristics that can't be expressed by a number. Is a mouse's fur smooth and full, or rough and patchy?

Scientists analyze data in different ways. Scientists often analyze their data by looking for patterns that help them to see a bigger picture that answers their original question.

Once you have performed an experiment and gathered data, what's the next step? Data isn't much help if it's just sitting in a pile of notebooks or in a disorganized spreadsheet. Scientists analyze the data they gather to look for patterns. To analyze data, they may arrange it as statistics in tables or charts that help them see patterns. Statistical analysis of their data on the differences they see between a control group and an experimental group can help scientists arrive at answers to their original question.

Photosynthesis is a process by which plants transfer light energy (sunlight) into chemical energy. The school picture shows a leaf with glucose in the center surrounded by circular arrows. Arrows point in labeled sunlight energy, carbon dioxide, and water. An arrow points out labeled oxygen.

One form of the sun's energy is radiant energy—the energy of light. Radiant energy in the form of sunlight strikes the leaf of a plant and triggers a whole cascade of events that ends in the production of a chemical form of energy—molecules of glucose. The plant uses the glucose to power all of its processes. The process by which plants transfer the energy of sunlight, along with carbon dioxide and water, into glucose is called photosynthesis.

Scientists draw conclusions by analyzing their data. Table shows Independent Variable =Dependent Variable Tail Length Number of Offspring Elongated 8 offspring Normal 5 offspring Reglued 5 offspring Shortened 3 offspring

One of the most basic questions to ask when analyzing data is, did manipulating the independent variable change the dependent variable? Møller and his team analyzed their data to see if manipulating tail length (the independent variable) had an impact on the number of an individual barn swallow's offspring (dependent variable). Now, look at the chart for the final data from the barn swallow study. What is your conclusion based on the data? Do you agree with Møller's conclusion that the data support his original hypothesis, "If a male barn swallow has long tail feathers, then he is likely to have more offspring than a male with short tail feathers"?

All living things depend on a source of energy for survival.

Organisms need energy to survive and grow. The primary source of energy is the sun. The common pattern of energy flow through the environment is this: Light from the sun drives photosynthesis; photosynthesis changes light, water, and carbon dioxide into glucose; organisms ingest glucose in the form of food; cells transfer digested food into ATP. Living organisms need energy to carry out all activities. Some living things get energy from sunlight. Others get energy from consuming other life-forms. A few get energy from chemicals. Living things cannot always use that energy directly; they convert some of that energy into the chemical compounds that support life.

Scientists communicate their findings. Scientists communicate their findings so that others may restudy, improve, or expand them. Pacific Yew In 1958, the National Cancer Institute launched a study that investigated more than 30,000 plants such as the Pacific yew for potential anticancer compounds

People like to talk about what's new, and scientists are no different from the rest of us: They share their news. This process is important for a number of reasons. For the field of biology to move forward, new discoveries need to be shared with other experts. If Tinbergen hadn't shared his discoveries with other scientists, we might not know as much about how animals learn. In a similar vein, we would not know much at all about the human genome if the scientists who decoded it kept that information to themselves. Sometimes information needs to be shared for the public good. For example, in the 1960s, scientists discovered that extracts from the bark of the Pacific yew prevented tumors from growing. Sharing this information made it possible for other scientists to determine the exact material in the bark that had this antitumor property. Today it is the active ingredient in a top-selling anticancer drug Taxol.

Evolution can help explain how communities and ecosystems are organized. Camels adapted to the desert with padded feet, a fat-storing hump, and nostrils that keep out sand.

Populations of organisms evolve within the context of a particular environment. This means those organisms are adjusted to the conditions—climate, vegetation, and neighboring species—where they live. Would you expect to find a polar bear in the middle of the mountainous cloud forests of Costa Rica? No—polar bears live in the Arctic, and their bodies are adapted to life there. Their white fur helps them blend in with snow and ice, and a thick layer of fat insulates their bodies from the cold. From the structure of their bodies to their behaviors, the entire community of organisms that calls the Arctic home is adapted to life there. Most scientists suggest that the diversity of life we see today came about through the long process of evolution, as populations adapted to conditions in the many different habitats on earth.

1.07 The Characteristics of Life 2 Scientists use biological organization to better understand the connections between living things and between the parts of any single living organism. A cell can be a single-celled organism or it can be part of a multi-cell organism that has specialized cells that make up tissues that make up organs that make up organ systems.

Rebecca Heald investigates structures that play a role in cell division. Ralph Fregosi examines how the nervous system controls breathing. Cynthia Hunter studies relationships between species on Hawaii's coral reefs. While each scientist studies a distinctly different field of biology, one theme unites their work: the principles of biological organization, from the cell to the ecosystem.

1.03 Scientific Processes 1 At the core of any scientific method is a question that can be tested experimentally. An experimental scientific method makes observations and asks questions, forms a hypothesis, designs an experiment, identifies variables, establishes experimental groups and control groups, performs an experiment, gathers and analyzes data, draws conclusions and communicates. If the hypothesis was wrong, the scientific method tells us to alter the hypothesis/form a new hypothesis and to start to design the experiment again (and continue the process).

Science is a multifaceted process based on observation and research, which lead to questions, hypotheses, experiments, and, one hopes, solid conclusions.

Scientists use many scientific methods to answer their questions about the natural world. Here are some of the ways you can use the scientific method: A biologist in the field studies the wing structure of a bat. Scientists often grow bacteria and viruses for laboratory experiments. Using a dip net, a scientist studies pond plants and animals in Australia. While studying a marine life, a biologist hitches a ride on a shark. Two scientists record data on plant growth in a controlled growing environment. Surrounded by banks of computers, a researcher looks for patterns in the data she collected and organized.

Scientific methods are not simply recipes or series of steps that scientists follow to answer questions about the natural world. Scientific methods actually refer to many processes that scientists follow in investigating phenomena—from the function of genes in your body to the function of organisms in an ecosystem. And scientific methods aren't just limited to scientists. You can adopt scientific processes in your approach to everyday life.

The basic unit of life is the cell.

Scientists often say the cell is the fundamental unit of life. But what does this mean? The cell is the most basic and essential part of an organism. The cell is the factory where the components of an organism are assembled, and it is the power plant that provides the organism with the energy it needs to survive. The cell contains genetic material, which gives the cell the blueprints for growth and development, and is passed from parents to offspring. How do cells provide these services? Cells are organized entities that contain numerous specialized structures called organelles that carry out many of the processes of life. Some organelles produce energy; others package wastes; others work as assembly lines, building molecules called proteins. Turn to page 48 in your reference book for more information on organelles.

Observation is a key process in science. Biologist Jane Goodall has studied chimpanzee behavior for more than 30 years. After stripping leaves from a twig, a chimpanzee "fishes" for ants in a tree. As ants crawl on the twig, the chimp eats the insects as if using an eating utensil.

Scientists sometimes rely heavily on observations to form conclusions about phenomena in the natural world. Biologist Jane Goodall, for example, has made careful observations of behaviors and interactions among the members of a chimpanzee population in eastern Africa. Goodall observed chimpanzees making and using tools. Until then, scientists thought only humans had that skill. Her observation was a significant breakthrough for the fields of animal behavior and primatology—the study of primates. In a similar way, many other scientific investigations start with observations of the natural world.

The structure of each component in a living organism reflects its function. Video Transcript: Screen 1: 00:00:00.00 Narrator: The chaffinch has a short, thick cone-like beak. Its shape is ideal for picking out seeds from pine cones. There's a relationship between the structure, or form of the chaffinch's beak and the function of the bird's beak. Let's look at some other birds to see how their beaks' form relates to their function. 00:00:22.00 The pelican's beak has a large expandable sac that allows it to net fish. 00:00:28.00 The strong, wide, flat beak of the duck is well suited for gathering and holding food. Bumps along the edge of the duck's beak filter water out without losing the food. 00:00:41.00 The long, sensitive, upturned beak of the pied avocet is ideal for catching small crustaceans. 00:00:49.00 The woodpecker's stout, chisel-like beaks allow it to drill holes in trees to obtain food or make a home. 00:00:57.00 The hawk's hooked beak can tear through the flesh of their prey. 00:01:02.00 The large, strong, curved beak of the macaw is designed to crush nuts and seeds. 00:01:10.00 His short, stout, cone-shaped beak makes it easy for the cardinal to open seeds and nuts. 00:01:17.00 The hummingbird's long and narrow beak lets it reach deep into flowers to drink nectar. 00:01:24.00 All of these birds have beaks, but each beak is different. The shape of each beak relates to the food the bird eats. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: There is a chaffinch bird on a pile of pinecones. The chaffinch is small and bluish-grey with brown, black and white markings. It occasionally pecks at the pinecones. 00:00:11.00 Narrator: The chaffinch has a short, thick cone-like beak. Its shape is ideal for picking out seeds from pine cones. There's a relationship between the structure, or form of the chaffinch's beak and the function of the bird's beak. Let's look at some other birds to see how their beaks' form relates to their function. 00:00:33.00 Description: There is a brown pelican in the water. The pelican catches something in the water and throws its head back to swallow it. There is a sac on the bottom-side of the beak. 00:00:44.00 Narrator: The pelican's beak has a large expandable sac that allows it to net fish. 00:00:49.00 Description: There are brown ducks along the water's edge. They are skimming the top of the water with their beaks. 00:00:56.00 Narrator: The strong, wide, flat beak of the duck is well suited for gathering and holding food. Bumps along the edge of the duck's beak filter water out without losing the food. 00:01:09.00 Description: There are pied avocets along the edge of the water. The bird is white with black markings and has long legs. One bird pulls something out of the water with its beak. 00:01:20.00 Narrator: The long, sensitive, upturned beak of the pied avocet is ideal for catching small crustaceans. 00:01:27.00 Description: There is a red, black, and white woodpecker perched on the side of a tree. It drills a hole in the side of the tree. 00:01:36.00 Narrator: The woodpecker's stout, chisel-like beaks allow it to drill holes in trees to obtain food or make a home. 00:01:43.00 Description: There is a brown and white hawk tearing apart a dead animal. 00:01:48.00 Narrator: The hawk's hooked beak can tear through the flesh of their prey. 00:01:52.00 Description: There is a colorful macaw perched on a plant. It has a piece of plant in its beak. 00:01:58.00 Narrator: The large, strong, curved beak of the macaw is designed to crush nuts and seeds. 00:02:05.00 Description: There is a red cardinal eating seeds. 00:02:08.00 Narrator: His short, stout, cone-shaped beak makes it easy for the cardinal to open seeds and nuts. 00:02:15.00 Description: There is a green, white, and black hummingbird flying in place. Its beak is in a long red flower. 00:02:23.00 Narrator: The hummingbird's long and narrow beak lets it reach deep into flowers to drink nectar. 00:02:29.00 Description: There are images of each bird described in the video. 00:02:33.00 Narrator: All of these birds have beaks, but each beak is different. The shape of each beak relates to the food the bird eats.

Scientists sometimes talk about structure-function relationships in living organisms. What does this mean? It refers to how the shape or architecture of a part of an organism relates to its function. The shape (structure) of a bird's beak, for example, often reflects how the bird eats (function). Likewise, the structure of your small intestine relates to its function in nutrient absorption. The small intestine is lined with millions of small projections of tissue that provide ample surface area for the absorption of nutrients from food. Like the bird's bill, the architecture of the small intestine enables the organ to perform its function. Explore some of the different shapes and functions of bird beaks.

Living organisms require energy, carry out many different chemical reactions, maintain homeostasis, and respond to their environments.

Staying alive is a lot of work. Energy is required for every single one of life's processes, from growth and development to reproduction to maintenance of the body's structures. It takes energy to release energy from the food we eat, and even to find food in the first place. In addition to finding and using energy, living organisms must also maintain homeostasis to function correctly. Different body systems help maintain homeostasis; organisms can respond to their environment in ways that maintain homeostasis, as well.

All organisms need to convert one kind of energy into another. The sun's energy cycles through the environment as predators eat plant eaters.

Take a moment to review how organisms get the energy they need to live. Plants capture light energy (sunlight) and transfer it during photosynthesis into chemical energy in the form of glucose. Animals eat plants and other organisms to get energy. They digest the food they eat, and their bodies break it down into glucose. Cellular respiration transfers the energy stored in glucose into ATP, the chemical energy that cells use to drive the processes of life.

1.01 Semester Introduction Biology Reference Guide: http://k12.kitaboo.com/eBookWs/ebook/science/science03/Launch.html#

Take a quick look at what you will study this academic semester. Unit 1 introduces biology Opens in modal popup window as a science, explaining the step-by-step processes that scientists follow as they seek to understand nature. You will also learn about key characteristics of life and energy. Unit 2 reviews some basic facts about chemistry that apply to all living things. You will learn about key chemical components of living things, including carbohydrates, proteins, lipids, and nucleic acids such as DNA and RNA. Unit 3 introduces cells—the building blocks of all living things. You will explore cell structure and function, including how cells get and use energy, how materials cross a cell membrane, and how cells reproduce. Units 4 and 5 deal with how living things pass traits from one generation to another. It begins with the work of Gregor Mendel, a pioneer in the field of genetics, and progresses through the modern understanding of genetics at the cellular level. Unit 6 is a semester review and test.

Living organisms maintain a constant set of conditions inside their bodies. Homeostasis African elephants flap their large ears in the air to help cool the blood that flows through them. Emerging from cold ocean waters, Galápagos marine iguanas absorb heat from the hot rocks and the sun. A dog stays cool by panting. Evaporation cools its tongue and the air drawn into the dog's lungs. A fawn avoids overheating by resting quietly in the shade, out of the direct sunlight. Since pigs don't really sweat like humans do, they rely on other sources of water for cooling evaporation. Turtles line up on a log to catch some warming rays from the sun. Surviving the cold Weddell Seal: When the air temperature gets too cold, Weddell seals seek refuge in warmer seawater, below the ice. They remain close to holes in the surface so they can breath.

The Weddell seal lives in one of the harshest places on earth: Antarctica. There, the wind chill can drop to -57°C, which is nearly three times as cold as the freezer in your kitchen. Yet Weddell seals maintain a consistently warm body temperature, just like you. This ability to maintain a constant set of internal conditions despite changes in the environment is homeostasis. Maintaining homeostasis is crucial to the health of all living organisms. Homeostasis can be thought of as a process in an entire organism, such as the Weddell seal, or in any one cell of an organism. For example, to work properly, most of the chemical reactions that take place in a cell and that are important to life require certain conditions, such as a limited range of temperatures or the right balance of acids and nonacidic substances. Cells have to maintain those conditions—that is, maintain homeostasis—for the cell to work properly. Explore some of the ways different animals maintain homeostasis.

All life is made of cells. Many processes of metabolism occur inside an organism's cells. Elodea cells carry out all the processes of life.

The cell is the smallest structure that has the ability to carry out all the processes of life. Cells grow and develop, reproduce, pass along genetic information, carry out chemical reactions, and respond to the environment. The organisms you see around you each day are made of billions, or even trillions, of cells. Other organisms, like bacteria, are made up of only one cell. Many of the structures inside cells carry out important roles in an organism's metabolism. Structures inside of a plant cell, for example, capture the sun's energy. Other structures convert this sunlight into chemical energy. Still other parts of the cells convert this to more usable forms of chemical energy.

The control group is key to interpreting the results of an experiment. All other conditions being equal, fertilized tomato plants usually yield more tomatoes.

The control group in an experiment gives you something to compare your experimental group to. That comparison allows you to verify your hypothesis. If your experimental manipulation produces a different outcome than what you see in your control group, then your manipulation had some kind of effect: The drug cured the common cold, or the fertilizer made your plant produce more tomatoes. For this reason, it is very important to make sure that your experimental conditions don't artificially affect your results.

Most experiments investigate how changing the independent variable affects the dependent variable. The CHART shows a row of Independent Variable= Dependent Variable: Longer Tail= Larger # of Offspring Normal Tail= Average # of Offspring Shorter Tail= Smaller # of Offspring

The independent variable is the variable that is carefully manipulated by the researcher in some way. Tail length is the independent variable in the barn swallow study. The dependent variable—the number of offspring—is the variable that is measured. It may help to think of the dependent variable as the variable that is dependent on the manipulation of the independent variable.

Some organisms use chemicals as a primary source of energy. The bodies of deep-sea tube worms contain bacteria that transfer chemicals into energy. A significant discovery: Scientists discovered hydrothermal vents and giant tube worms only recently, in 1977. The discovery of bacteria that produce food through chemosynthesis was one of the most significant in years.

There are a few organisms that do not depend directly on the sun's energy. At the bottom of the ocean are structures called hydrothermal vents—cracks in the surface of the earth from which hot water and sulfur-rich chemicals spew into the ocean. The bodies of giant tube worms that live near those vents contain bacteria that use the chemicals to make glucose. They do so in a process called chemosynthesis . Chemicals, rather than sunlight, are the primary source of energy for those deep-sea bacteria.

The platypus is a marvel of the living world.

This odd-looking animal is a duck-billed platypus—a marvel of the living world. The platypus is native to Tasmania and parts of Australia. It's unusual in that it is a mammal that lays eggs. To fully understand this animal—and all living things, from the familiar to the unusual—you have to immerse yourself in the science of cell biology, among other biological sciences. This semester's lessons are designed to help you make progress toward that goal.

A hypothesis can be tested through experimentation. For many studies of bird behavior, biologists trap birds in mist nets.

To test the hypothesis "If a male has long tail feathers, then he is likely to have more offspring than a male with short tail feathers," you might begin by identifying which characteristics or variables to investigate. In this case, tail length is the characteristic of interest. Møller and his colleagues tested their hypothesis by experimentally manipulating tail length in a group of barn swallows, and observing which males were the most successful at finding mates and having offspring. In those experiments, the only variable that Møller and his team wanted to test was tail length. To keep all other variables the same, the team observed all birds in the same setting; the scientists didn't manipulate any other parts of the birds, such as wing feathers, color, or beak size. Turn to page 10 in your reference book for an overview of scientific methods.

Experiments help scientists test their hypotheses.

To test their hypotheses, scientists perform carefully planned procedures called experiments. Tinbergen set up an experiment to test his hypothesis that wasps use visual clues or landmarks to find their nests. While the female was inside the nest, he arranged a number of pinecones in a ring around the nest. After the wasp left to hunt, he moved the pinecones and arranged them in a similar ring several feet away from the nest. When the female returned, she flew not to her nest, but to the center of the ring of pinecones. The experiment required the comparison of different sets of circumstances. By showing wasps one set of landmarks and then moving those landmarks to a new location (changing the circumstances), Tinbergen was able to figure out what clues help wasps find their way home. He also tested the hypothesis that wasps can learn to recognize new landmarks.

Scientists ask questions based on their observations of the natural world. Nikko Tinbergen observed wasp behavior, asked a question about it, and began seeking answers.

True to her name, the female digger wasp digs a nest in the ground in which she lays her eggs. She leaves the nest, hunts, and returns to feed the larvae growing in the nest. After observing the wasp's behavior, biologist Nikolaas "Nikko" Tinbergen asked, "How does she know where her nest is located?" Tinbergen's study is a good example of the process of science. Tinbergen made observations of the natural world and posed a question based on those observations. To find an answer, he then developed a hypothesis that digger wasps rely on landmarks to find their nests, and developed an experiment to explore that hypothesis.

Multicell organisms have specialized cells. To see the various kinds of cells that make up your hand, turn to pages 74 and 75 in your reference book.

Unlike bacteria, you are made up of trillions of cells. But not all cells in your body look and behave in the same way. For example, cells that make up your skin look and act very differently than the cells that make up your nervous system. Skin cells are fairly flat in shape and contain a pigment called melanin, which helps protect your skin from ultraviolet rays. Most cells in your nervous system, on the other hand, are long and branched, and do not contain melanin. Skin cells and nerve cells are examples of specialized cells. They have all the components you'd expect to find in a cell, such as a nucleus and other structures. However, they also perform unique functions that are enhanced by their structure.

Scientists communicate their results to other scientists and to the public. Scientific information from a variety of sources is often used by public figures to alert us to the dangers of, and solutions to, environmental problems. What if? Sometimes, the results of a study do not agree with the hypothesis. What happens then? The scientist should conclude that the results don't actually support the hypothesis. Then, she would alter her hypothesis, design a new experiment, and begin a new study.

When Møller's team finished their study, one of the first things they did was write up a report of their findings and publish it in a scientific journal. Scientific journals are magazines that contain research reports from scientists in a particular field. They are read not only by scientists, but also by the media, government officials, and people in industry or other organizations. Publishing in a journal is just one way in which scientists communicate their findings. You probably know that scientists sometimes communicate not only with other scientists, but with the general public as well.

1.04 Scientific Processes 2 Collecting and analyzing data, forming conclusions, and communicating results are important steps in a scientific method.

When you turn on the TV and see reports about climate change or the latest medical breakthrough, you're observing one important part of a scientific method: communication. Long before those scientists informed the public about their research, however, they performed rigorous experiments to test their hypotheses.

People respond to changes in their environment. Shivering, sweating, getting sprinkled, and bundling up are all ways humans maintain the correct body temperature. High Altitude Adaptation Mountaineer: A breath of air on top of a mountain contains up to 40% fewer oxygen molecules than a breath of fresh air at sea level. For this reason, mountaineers spend several days allowing their bodies to respond to the lower levels of oxygen available at high altitude. Over those days, the body produces extra red blood cells, which carry oxygen throughout the body. This way, very little oxygen that is inhaled is wasted.

You also respond to changes in your environment, although you might not have thought about it in terms of homeostasis. On a hot summer day you begin to sweat—a mechanism by which your body tries to get rid of excess heat. On a cold day, you might feel yourself shiver. Why? Shivering is a process by which your body tries to generate heat by causing rapid muscle contractions. By changing your behavior, you also help your body maintain homeostasis. Something as simple as wearing a heavy coat in the winter helps your body maintain its internal conditions.

Specialized cells and tissues make up organs, and groups of organs make up organ systems.

You can probably name many organs—the next level of organization. Your heart, lungs, brain, and kidneys are all organs. An organ is made up of two or more tissues and has a specific function. Most organs in your body have a combination of all four types of tissue: epithelial, connective, muscle, and nerve. The highest level or organization in your body is the organ system. Organs in your body are arranged into organ systems, or groups that function together. For example, your digestive system includes the mouth, stomach, and intestines, each of which plays a role in breaking down food and extracting nutrients from it. Turn to page 148 in your reference book for more information on digestive systems.

Organisms pass along the genetic material DNA to their offspring. Blond hair is just one of the genetic traits passed on from these parents to their children.

You have just learned that evolutionary adaptations are passed from parents to offspring. This process is called heredity, and it is one of the basic characteristics of life. All living organisms pass genetic information to their offspring. For heredity to work, a parent must pass along to the next generation all the information necessary to generate another organism like itself. This information is encoded in the molecule deoxyribonucleic acid (DNA). This molecule contains genes that provide the instructions for growth and development. In other words, genes play an important role in determining an organism's characteristics.

Life on earth is organized into populations, communities, ecosystems, and biomes. From Cells to Biomes Characteristics of Life: Living things meet the challenges of getting and using energy, growing, reproducing, and maintaining their structure. Living things share the following essential characteristics: cellular organization, metabolism, homeostasis, growth and development, response, and heredity. Multicell Organization: Organisms with many cells have opportunities and challenges that single-cell organisms do not have. A living thing that has many cells can have new capabilities, more complex responses, and the benefits of being larger. However, multicellularity most often requires specialized tissues and organs to meet the challenges of life, including those brought on by the new structures and increased size. Cellular Organization: The cell is the fundamental unit of life. Some organisms are unicellular. Those that are multicellular generally have cells that perform specialized functions. These cells may be arranged into tissues, the tissues arranged into organs, and organs arranged into systems with major functions. Populations and Ecosystems: Individuals exist in populations. All the different populations in an area form a community. The community and the local environment make up an ecosystem, which may change over time. Large geographic areas dominated by specific kinds of plants and animals are called biomes. Organism Interactions: Individuals interact with their living and nonliving environments. They compete for limited resources, such as space, food, water, and mates. Individuals are involved in relationships with other life-forms and respond to their environment through innate and learned behaviors.

You have learned about the levels of structural organization in multicell organisms: cells, tissues, organs, organ systems, and the organism itself. But the study of biological organization does not end with the organism. Organisms interact with one another to form still more levels of organization: populations, communities, ecosystems, and biomes. By studying how organisms interact with one another at each level, scientists are learning to describe and understand how ecosystems work. An ecosystem is a limited geographical area that has similar biotic and abiotic factors. An ecosystem can be as small as a log or as big as an immense forest. Knowing about populations and ecosystems is helpful in developing plans for the protection of endangered species, developing policies to minimize the environmental impact of new developments such as housing and businesses, and even combating the spread of exotic or disease-carrying species. Explore some examples of how ecosystems are organized:

Organisms convert most foods into glucose. The food animals eat is digested into smaller particles, some of which are ultimately transferred into glucose.

You know the old saying "You are what you eat"? Everyone knows that energy comes from the food they eat. Think about the pizza you had last night or that apple you just munched on. For a coyote, food might be a rabbit or a mouse. For a deer or gazelle, food might be grass or leaves. But no food provides energy immediately. Organisms must first digest large pieces of food into smaller ones. In the process, the energy in many of those food particles is ultimately transferred into glucose.

Scientists ask questions and develop hypotheses. Robert Koch, after studying the reports of earlier scientists, developed the germ theory of disease. Nikko Tingbergen Nikko Tinbergen was awarded a Nobel Prize in 1973 in recognition of the significance of his research on animal behavior. He is considered one of the fathers of ethology, the scientific study of animal behavior.

You may already have learned that scientists test their hypotheses through experiments. But where do their hypotheses come from? A hypothesis is an assumption about what will happen during an experiment or an observation. It's not a wild guess, however, but one based on reason and experience. Scientists don't just make up a hypothesis out of the blue. Often, they base hypotheses on observations they've already made, or they study the work of other scientists to learn what kinds of questions haven't yet been tested. A hypothesis can also stem from a question a scientist has. In his study of digger wasp behavior, Tinbergen questioned how wasps find their nests. He hypothesized that wasps use visual clues, so he tested the hypothesis that wasps use visual clues or landmarks to find their nests. He also tested the hypothesis that wasps can learn to recognize new landmarks.

1.06 The Characteristics of Life All living things must meet the challenges of getting and using energy, growing, reproducing, and maintaining their structure. Seven shared characteristics of all living things include: metabolism heredity cellular organization homeostasis reproduction response growth and development

You probably have an intuitive understanding of life. Living organisms grow, they move, and they change over time, right? Well, there's more to it than that. Sand dunes on the beach grow, move, and change over time, but they're not alive. What's the difference? Read on to learn about the characteristics that separate living and nonliving things.

Living organisms are made of organic compounds that contain carbon. The cells of all organisms, whether a microscopic amoeba or the largest plants and animals, are made up of organic compounds.

You've just learned about the levels of structural organization found in living organisms. But what exactly are cells, tissues, and organs made of? Living organisms are made of types of molecules called organic compounds. Each of these molecules is based on the element carbon. All living organisms are made up primarily of four major types of molecules: lipids, carbohydrates, proteins, and nucleic acids. For now, just remember that living organisms, from the smallest bacteria to the largest whale, are made of molecules that contain carbon.

1.09 Energy and Life Every living thing needs energy to survive. The sun's energy is absorbed by plants and transferred into glucose. Animals eat the plants whose energy is transferred into ATP.

Your body performs thousands of tasks that do not require your conscious effort, such as blinking, making new skin cells, and sending messages to your brain. Whether you act consciously or not, every single thing you do requires energy. The same is true for all living things. Energy plays a crucial role in life.

Population

all of the members of one species that live in a common area and whose population dynamics are different from those of other populations

Community

all of the populations that live and interact with each other in a particular area

hypothesis \hiy-PAH-thuh-sis\

an assumption that is made as a result of gathering data through sampling

Organism

any living thing that takes in food, grows, and reproduces

The structure of an organism's body parts relates to the function of those parts. The Marine Iguana: Dark Skin: After swimming in the cold ocean, the marine iguana needs to warm up quickly. Dark skin color absorbs more heat from the sun than light skin color. Blunt Snout: The marine iguana eats algae that grows on underwater rocks. Its blunt snout helps the lizard get close to the rock to get a good grip on the algae. Partially Webbed Feet: The marine iguana gets its food from the ocean. Its partially webbed feet help it swim. A Different Adaptation Land Iguana: Unlike the marine iguana of the Galápagos Islands, the land iguana does not get its food from the ocean. Land iguanas have longer snouts and no webbing on their feet. Transcript (Video with Audio Description) Screen 1: 00:00:00.00 Description: There is a scene of a rocky beach with approximately 40 iguanas. 00:00:06.00 Narrator: The Galapagos marine iguana has a number of beneficial mutations that allow it to swim under water to eat the algae that grows on rocks. Their skin is dark black, so it warms quickly in the sunlight, preparing the marine iguana to swim in the cold ocean water. 00:00:27.00 Description: The iguana has spikes along its back 00:00:37.00 Description: A white arrow points to the feet of the iguana. 00:00:42.00 Narrator: Their feet are webbed to help them swim. 00:00:47.00 Description: A white arrow points to the snout of the iguana 0:00:51.00 Narrator: The snout of the marine iguana is blunt, allowing its teeth to get as close to the rocks as possible. 00:01:09.00 Description: A white arrow points to the tail of the iguana. 00:01:14.00 Narrator: The tail is flattened and moves side to side like a fish to propel the iguana through the water. Ending Time: 00:01:21.00

magine taking a trip to a remote island. You notice some strange-looking lizards hanging out on the beach. As you observe one lizard closely, you begin to notice certain things, such as its skin color and the shape of its feet. You wonder why the lizard's body looks the way it does. Study the lizard in the photo and its labeled body parts. Why might the lizard's body have that particular shape or color? When you have some answers, explore further to read how the structure of each body part relates to how the lizard uses that part.

chemosynthesis

the creation of glucose using energy from a chemical source rather than from sunlight