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- Herausgeber: John Wiley & Sons
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
- Veröffentlichungsjahr: 2017
The ultimate guide to understanding biology Have you ever wondered how the food you eat becomes the energy your body needs to keep going? The theory of evolution says that humans and chimps descended from a common ancestor, but does it tell us how and why? We humans are insatiably curious creatures who can't help wondering how things work--starting with our own bodies. Wouldn't it be great to have a single source of quick answers to all our questions about how living things work? Now there is. From molecules to animals, cells to ecosystems, Biology For Dummies answers all your questions about how living things work. Written in plain English and packed with dozens of enlightening illustrations, this reference guide covers the most recent developments and discoveries in evolutionary, reproductive, and ecological biology. It's also complemented with lots of practical, up-to-date examples to bring the information to life. * Discover how living things work * Think like a biologist and use scientific methods * Understand lifecycle processes Whether you're enrolled in a biology class or just want to know more about this fascinating and ever-evolving field of study, Biology For Dummies will help you unlock the mysteries of how life works.
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Biology For Dummies®, 3rd Edition
Published by: John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030-5774, www.wiley.com
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Published simultaneously in Canada
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ISBN 978-1-119-34537-4 (pbk); ISBN 978-1-119-34538-1 (ebk); ISBN 978-1-119-34541-1 (ebk)
Biology For Dummies®
To view this book's Cheat Sheet, simply go to www.dummies.com and search for “Biology For Dummies Cheat Sheet” in the Search box.
Table of Contents
Cover
Introduction
About This Book
Foolish Assumptions
Icons Used in This Book
Beyond the Book
Where to Go from Here
Part 1: Biology Basics
Chapter 1: Exploring the Living World
It All Starts with a Cell
Life Begets Life: Reproduction and Genetics
Making the Connection between Ecosystems and Evolution
Getting Up Close and Personal with the Anatomy and Physiology of Animals
Comparing Plants to People
Chapter 2: How Life Is Studied
Living Things: Why Biologists Study Them and What Defines Them
Making Sense of the World through Observations
Seeing Science as the Constant Sharing of New Ideas
Tracking Down Scientific Information
Chapter 3: The Chemistry of Life
Exploring Why Matter Matters
Recognizing the Differences between Atoms, Elements, and Isotopes
Molecules, Compounds, and Bonds
Acids and Bases (Not a Heavy Metal Band)
Carbon-Based Molecules: The Basis for All Life
Chapter 4: The Living Cell
An Overview of Cells
Peeking at Prokaryotes
Examining the Structure of Eukaryotic Cells
Cells and the Organelles: Not a Motown Doo-wop Group
Presenting Enzymes, the Jump-Starters
Chapter 5: Acquiring Energy to Run the Motor
What’s Energy Got to Do with It?
Photosynthesis: Using Sunlight, Carbon Dioxide, and Water to Make Food
Cellular Respiration: Using Oxygen to Break Down Food for Energy
Energy and Your Body
Part 2: Let’s Talk about Sex, Baby: Cell Reproduction and Genetics
Chapter 6: Dividing to Conquer: Cell Division
Reproduction: Keep On Keepin’ On
Welcome to DNA Replication 101
Cell Division: Out with the Old, In with the New
How Sexual Reproduction Creates Genetic Variation
Chapter 7: Making Mendel Proud: Understanding Genetics
Why You’re Unique: Heritable Traits and the Factors Affecting Them
“Monk”ing Around with Peas: Mendel’s Laws of Inheritance
Diving into the Pool of Genetic Terminology
Bearing Genetic Crosses
Studying Genetic Traits in Humans
Moving Beyond Mendel
Chapter 8: Reading the Book of Life: DNA and Proteins
Proteins Make Traits Happen, and DNA Makes the Proteins
Moving from DNA to RNA to Protein: The Central Dogma of Molecular Biology
Mistakes Happen: The Consequences of Mutation
Giving Cells Some Control: Gene Regulation
Chapter 9: Engineering the Code: DNA Technology
Understanding Just What’s Involved in DNA Technology
Mapping the Genes of Humanity
Genetically Modifying Organisms
Part 3: It’s a Small, Interconnected World
Chapter 10: Exploring the Living World: Biodiversity and Classification
Biodiversity: Recognizing How Our Differences Make Us Stronger
Meet Your Neighbors: Looking at Life on Earth
Climbing the Tree of Life: The Classification System of Living Things
Chapter 11: Observing How Organisms Get Along
Ecosystems Bring It All Together
Studying Populations Is Popular in Ecology
Moving Energy and Matter around within Ecosystems
Chapter 12: Evolving Species in an Ever-Changing World
What People Used to Believe
How Charles Darwin Challenged Age-Old Beliefs about Life on Earth
The Evidence for Biological Evolution
Why So Controversial? Evolution versus Creationism
How Humans Evolved
Part 4: Systems Galore! Animal Structure and Function
Chapter 13: Pondering the Principles of Physiology
Studying Function at All Levels of Life
Wrapping Your Head around the Big Physiological Ideas
Chapter 14: Moving and Shaking: Skeletal and Muscular Systems
Doing the Locomotion, Animal-Style
The Types of Skeletal Systems
Why Muscles Are So Essential
Chapter 15: Going with the Flow: Respiratory and Circulatory Systems
Passing Gas: How Animals “Breathe”
Circulation: Nutrients In, Garbage Out
Getting to the Heart of Simpler Animals
Exploring the Human Heart and Circulatory System
A Bloody-Important Fluid
Chapter 16: Checking Out the Plumbing: Animal Digestive and Excretory Systems
Obtaining Food and Breaking It Down
The Ins and Outs of Digestive Systems
Traveling through the Human Digestive System
Absorbing the Stuff Your Body Needs
What’s for Dinner? Making Wise, Nutritious Food Choices
Exploring the Human Excretory System
Chapter 17: Fighting Back: Human Defenses
Microbial Encounters of the Best and Worst Kinds
Built to Protect You: Innate Human Defenses
Learning a Lesson: Adaptive Human Defenses
Giving Your Defenses a Helping Hand
Aging and Ailing: Changes in the Immune System
Chapter 18: The Nervous and Endocrine Systems, Messengers Extraordinaire
The Many Intricacies of Nervous Systems
What a Sensation! The Brain and the Five Senses
Following the Path of Nerve Impulses
The Endocrine System: All Hormones Are Not Raging
Chapter 19: Reproduction 101: Making More Animals
This Budding’s for You: Asexual Reproduction
The Ins and Outs of Sexual Reproduction
How Other Animals Do It
Developing New Humans
Differentiation, Development, and Determination
Part 5: It’s Not Easy Being Green: Plant Structure and Function
Chapter 20: Living the Life of a Plant
Presenting Plant Structure
Obtaining Matter and Energy for Growth
Going It Alone: Asexual Reproduction
Mixing Sperm and Eggs: Sexual Reproduction
Chapter 21: Probing into Plant Physiology
How Nutrients, Fluids, and Sugars Move through Plants
Sending Signals with Plant Hormones
Part 6: The Part of Tens
Chapter 22: Ten Great Biology Discoveries
Seeing the Unseen
Discovering Penicillin, the First Antibiotic
Protecting People from Smallpox
Defining DNA Structure
Finding and Fighting Defective Genes
Discovering Modern Genetic Principles
Evolving the Theory of Natural Selection
Formulating Cell Theory
Amplifying DNA with PCR
Editing DNA with CRISPR
Chapter 23: Ten Ways Biology Affects Your Life
Keeping You Fed
Putting Microbial Enzymes to Work
Designing Genes
Powering the Planet
Causing and Treating Infectious Disease
Staying Alive
Providing You with Clean Water
Changing Physically and Mentally
Creating Antibiotic-Resistant Bacteria
Facing Extinction
About the Author
Connect with Dummies
End User License Agreement
Guide
Cover
Table of Contents
Begin Reading
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Introduction
Life is all around you, from invisible microbes and green plants to the other animals with whom you share the Earth. What’s more, these other living things aren’t just around you — they’re intimately interconnected with your life. Plants make your food and provide you with oxygen, microbes break down dead matter and recycle materials that all living things need, and insects pollinate the plants you rely on for food. Ultimately, all living beings rely on other living beings for their survival.
What makes biology so great is that it allows you to explore the interconnectedness of the world’s organisms and really understand that living beings are works of art and machines rolled into one. Organisms can be as delicate as a mountain wildflower, as curious as a grasshopper, or as awe-inspiring as a majestic elephant. And regardless of whether they’re plants, animals, or microbes, all living things have numerous working parts that contribute to the function of the whole being. They move, obtain energy, use raw materials, and make waste, whether they’re as simple as a single-celled organism or as complex as a human being.
Biology is the key you need to unlock the mysteries of life. Through it, you discover that even single-celled organisms have their complexities, from their unique structures to their diverse metabolisms. Biology also helps you realize what a truly miraculous machine your body is, with its many different systems that work together to move materials, support your structure, send signals, defend you from invaders, and obtain the matter and energy you need for growth.
About This Book
Biology For Dummies, 3rd Edition, takes a look at the characteristics all living things share. It also provides an overview of the concepts and processes that are fundamental to living things. We make sure to emphasize the most important ideas in biology while taking a look at the diversity of life on planet Earth and our place in it.
Within this book, you may note that some web addresses break across two lines of text. If you’re reading this book in print and want to visit one of these web pages, simply key in the web address exactly as it’s noted in the text, pretending as though the line break doesn’t exist. If you’re reading this as an e-book, you’ve got it easy — just click the web address to be taken directly to the web page.
Foolish Assumptions
As we wrote this book, we tried to imagine who you are and what you need in order to understand biology. Here’s what we came up with:
You’re a high school student taking biology, possibly in preparation for an advanced placement test or college entrance examination. If you’re having trouble in biology class and your textbook isn’t making much sense, try reading the relevant section of this book first to give yourself a foundation and then go back to your textbook or notes.
You’re a college student who isn’t a science major but is taking a biology class to help fulfill your degree requirements. If you want help following along in class, try reading the relevant sections in this book before you go to a lecture on a particular topic. If you need to fix a concept in your brain, read the related section after class.
You’re someone who just wants to know a little bit more about the living world around you. Good news … this book is your oyster! Read it at your leisure, starting with whatever topic fascinates you most. We include several examples of how biology impacts everyday life to help keep your interest piqued.
Icons Used in This Book
We use some of the familiar For Dummies icons to help guide you and give you new insights as you read the material. Here’s the scoop on what each one means.
The information highlighted with the Remember icon is stuff we think you should permanently store in your mental biology file. If you want a quick review of biology, scan through the book reading only the paragraphs marked with Remember icons.
The Technical Stuff icon marks extra information that isn’t necessary to understanding the material in the chapter. If you want to take your understanding of biology to a higher level, or if you just want to build your knowledge base of interesting facts, incorporate these paragraphs into your reading. If you just want the basics and don’t want to bother with nonessential information, skip them.
The Tip icon marks pointers that help you remember the facts presented in a particular section so you can better commit them to memory.
Beyond the Book
In addition to the material in the print or e-book you’re reading right now, this product also comes with some access-anywhere goodies on the web. Check out the free Cheat Sheet for more on human biology and physiology, natural selection and biological evolution, and biological reproduction and cell division. To get this Cheat Sheet, simply go to www.dummies.com and type Biology For Dummies Cheat Sheet in the Search box.
Where to Go from Here
Where you start reading is up to you. However, we do have a few suggestions:
If you’re currently in a biology class and having trouble with a particular topic, jump right to the chapter or section featuring the subject that’s confusing you.
If you’re using this book as a companion to a biology class that’s just beginning, you can follow along with the topics being discussed in class.
Whatever your situation, the table of contents and index can help you find the information you need.
Part 1
Biology Basics
IN THIS PART …
Take a look at the big picture of life on Earth.
Go behind the scenes of scientific investigation.
Explore the connections between chemistry and biology.
Discover life at the level of a single cell.
Delve into the details of how cells get energy.
Chapter 1
Exploring the Living World
IN THIS CHAPTER
Seeing how cells are part of all living things
Finding out the fundamentals of where babies come from and why you have the traits you do
Recognizing that all of Earth’s ecosystems are interconnected
Surveying animal anatomy and physiology
Exploring the similarities and differences between plants and people
Biology is the study of life, as in the life that covers the surface of the Earth like a living blanket, filling every nook and cranny from dark caves and dry deserts to blue oceans and lush rain forests. Living things interact with all of these environments and each other, forming complex, interconnected webs of life. For many people, a hike in the forest or a trip to the beach is a chance to reconnect with the natural world and enjoy the beauty of life.
In this chapter, we give you an overview of the big concepts of biology. Our goal is to show you how biology connects to your life and to give you a preview of the topics we explore in greater detail later in this book.
It All Starts with a Cell
Quick. What’s the smallest living thing you can think of? (Here’s a hint: Try to recall the basic properties of life; if you can’t, head to Chapter 2 to discover what they are.) Your mind may automatically call up images of ants, amoebas, or bacteria, but that’s not quite the answer. The absolute smallest unit of life is a single cell.
Everything an organism’s body does happens because its cells make those actions happen, whether that organism is a single-celled E. coli bacteria or a human being made up of approximately 10 trillion cells.
Of course, the number of cells you have isn’t the only difference between you and E. coli. The structure of your cells is a little bit different — your cells have more specialized internal compartments, such as the nucleus that houses your DNA (we cover cell structure in Chapter 4). Yet you have some distinct similarities as well. Both you and E. coli are made up of the same raw materials (flip to Chapter 3 to find out what those are) and have DNA as your genetic material (more on DNA in Chapter 8). You also use food the same way (see Chapter 5), and you build your proteins in the same manner (see Chapter 8).
Life Begets Life: Reproduction and Genetics
You began life as a single cell, when a sperm cell from your dad met an egg cell from your mom. Your parents made these reproductive cells through a special type of cell division called meiosis (we explain meiosis in detail in Chapter 6). When their reproductive cells combined, your dad and mom each donated half of your genetic information — 23 chromosomes from mom and 23 from dad — for a total of 46 chromosomes in each of your cells. The genes on those 46 chromosomes determined your characteristics, from your physical appearance to much of your behavior. The science of genetics tracks the inheritance of genes and studies how they determine traits (see Chapter 7). Through genetics, you can understand why your skin is a certain color or why some traits seem to run in your family.
Your genes are found in your DNA, which is in turn found in your chromosomes. Each chromosome consists of hundreds of different blueprints that contain the instructions for your cells’ worker molecules (which are mostly proteins). Each type of cell in your body uses the blueprints found in your genes to build the proteins it needs to do its particular job. So what exactly does all that mean? Here it is, plain and simple: DNA determines your traits because it contains the instructions for the worker molecules (proteins) that make your traits happen.
Scientists are discovering more and more about DNA; they’re also developing tools to read and alter the DNA in cells (see Chapter 9). Chances are you’re already experiencing the impacts of scientists’ work with DNA, even if you don’t know it. Why? Because scientists use recombinant DNA technology to alter organisms used in food and medicines. This technology allows them to take genes from one organism and place them into the cells of another, changing the characteristics of the receiving organism. For example, scientists alter the cells of bacteria with human genes, turning them into tiny living factories that produce human proteins needed to treat diseases.
Making the Connection between Ecosystems and Evolution
As you discover in Chapter 10, the amazing diversity of life on Earth helps ensure that life continues in the face of environmental change. Each type of organism plays a role in the environment, and each one is connected to the other. Green organisms such as plants combine energy and matter to make the food on which all life depends, herbivores eat plants, predators hunt prey, and decomposers such as bacteria and fungi recycle dead matter so it becomes available again to other living things. (For more on the interconnectedness of all living things on Earth, head to Chapter 11.)
Organisms such as plants form the foundation of every web of life (ecosystem) because they can combine energy and matter from the environment to make food. All organisms use food to get the energy they need to stay alive and the matter they need to grow. Ultimately, energy flows from the sun to plants, to organisms that eat other organisms, and then back out to the atmosphere (and ultimately outer space) as heat. At the same time, matter constantly cycles from the environment to the bodies of living things, then back out to the environment again. (For more on the flow of matter and energy, head to Chapter 11.)
Humans are part of the natural world, and like all living things, use resources from the environment and produce wastes. However, the human species is unusual in its ability to use technology to extend its reach, drawing heavily on the natural resources of the Earth and changing environments to suit its needs. The human population has expanded to cover most of the Earth, and the numbers just keep on growing.
Yet as humans draw more heavily upon the Earth’s resources, we’re putting stress on many other species and possibly driving them to extinction. The great lesson of biological evolution (a topic we cover in Chapter 12) is that not only do populations change over time but they’re also capable of going extinct. The challenge that humans face today is discovering ways to get what we need but still live in balance with the Earth’s various ecosystems.
Getting Up Close and Personal with the Anatomy and Physiology of Animals
All animals work hard to maintain homeostasis, or internal balance, as change occurs in the environment around them (see Chapter 13 for more on homeostasis). In a complex, multicellular animal like you, all of your organ systems must work together to maintain homeostasis.
Following is a rundown of all of your organ systems, including what they do and what they consist of:
Skeletal system:
Provides support, helps with movement, and forms blood cells. Made up of your bones (see
Chapter 14
).
Muscular system:
Enables movement. Consists of your skeletal, smooth, and cardiac muscles (see
Chapter 14
).
Respiratory system:
Brings in oxygen and expels carbon dioxide. Made up of your lungs and airways (see
Chapter 15
).
Circulatory system:
Transports materials throughout the body. Consists of your heart, blood, and blood vessels (see
Chapter 15
).
Digestive system:
Takes up nutrients and water and eliminates wastes. Made up of your stomach, intestines, liver, and pancreas (see
Chapter 16
).
Excretory system:
Maintains the balance of water and electrolytes in your body and removes wastes. Consists of your kidneys and bladder (see
Chapter 16
).
Integumentary system:
Serves as your first line of defense against infection. Made up of your skin (see
Chapter 17
).
Immune system:
Defends against foreign invaders. Consists of your thymus, spleen, lymphatic vessels, and lymph nodes (see
Chapter 17
).
Nervous system:
Controls your body functions via electrical signals. Made up of your brain, spinal cord, and nerves (see
Chapter 18
).
Endocrine system:
Produces hormones that control your body functions. Consists of your glands (see
Chapter 18
).
Reproductive system:
Is responsible for sexual reproduction. Made up of ovaries, fallopian tubes, a uterus, a cervix, a vagina, and a vulva if you’re female, and testes, a scrotum, vas deferens, a prostate gland, seminal vesicles, and a penis if you’re male (see
Chapter 19
).
Comparing Plants to People
At first glance, plants seem pretty different from people, but actually humans and plants occupy nearby branches on the tree of life. Both humans and plants engage in sexual reproduction, meaning they produce new offspring from the fusion of sperm and eggs that contain half the genetic material of the parents (see Chapter 20 for more information on how plants reproduce). Also like you, plants have systems for moving materials throughout their bodies (flip to Chapter 21 for the scoop on this), and they even control their functions with hormones.
Of course, plants also have major differences from humans. Most importantly, they make their own food using carbon dioxide, water, and energy from the Sun, whereas humans have to eat other organisms to survive. As a byproduct of their food production, plants give off oxygen as waste. Humans gladly breathe oxygen in and return the favor by breathing out carbon dioxide that the plants can use to make food (see Chapter 5 for more on photosynthesis and respiration and how they lead to this gas exchange between humans and plants).
Chapter 2
How Life Is Studied
IN THIS CHAPTER
Studying life
Using observations to solve the world’s mysteries
Recognizing science as an ever-changing thing
Discovering where to find scientists’ research and conclusions
Biology wouldn’t have gotten very far as a science if biologists hadn’t used organized processes to conduct their research or if they hadn’t communicated their research results with others. This chapter explores the characteristics that distinguish living things from the nonliving materials in the natural world. It also introduces you to the methods scientists (whether they’re biologists, physicists, or chemists) use to investigate the world around them and the tools they use to communicate what they’ve discovered.
Living Things: Why Biologists Study Them and What Defines Them
Biologists seek to understand everything they can about living things, including
The structure and function of all the diverse living things on planet Earth
The relationships between living things
How living things grow, develop, and reproduce, including how these processes are regulated by DNA, hormones, and nerve signals
The connections between living things, as well as the connections between living things and their environment
How living things change over time
How DNA changes, how it’s passed from one living thing to another, and how it controls the structure and function of living things
Defining what it means to be alive
An individual living thing is called an organism. Organisms are part of the natural world — they’re made of the same chemicals studied in chemistry and geology, and they follow the same laws of the universe as those studied in physics. What makes living things different from the nonliving things in the natural world is that they’re alive. Granted, life is a little hard to define, but biologists have found a way.
All organisms share eight specific characteristics that define the properties of life:
Living things are made of cells that contain DNA.
A
cell
is the smallest part of a living thing that retains all the properties of life. In other words, it’s the smallest unit that’s alive.
DNA,
short for
deoxyribonucleic acid,
is the genetic material, or instructions, for the structure and function of cells. (We fill you in on cells, including the differences between plant and animal cells, in
Chapter 4
, and we tell you all about the structure of DNA in
Chapter 3
.)
Living things maintain order inside their cells and bodies.
One law of the universe is that everything tends to become random over time. According to this law, if you build a sand castle, it’ll crumble back into sand over time. You never see a castle of any kind suddenly spring up and build itself or repair itself, organizing all the particles into a complicated castle structure. Living things, as long as they remain alive, don’t crumble into little bits. They constantly use energy to rebuild and repair themselves so that they stay intact. (To find out how living things obtain the energy they need to maintain themselves, turn to
Chapter 5
.)
Living things regulate their systems.
Living things maintain their internal conditions in a way that supports life. Even when the environment around them changes, organisms attempt to maintain their internal conditions. Think about what happens when you go outside on a cool day without wearing a coat. Your body temperature starts to drop, and your body responds by pulling blood away from your extremities to your core in order to slow the transfer of heat to the air. It may also trigger shivering, which gets you moving and generates more body heat. These responses keep your internal body temperature in the right range for your survival even though the outside temperature is low. (When living things maintain their internal balance, that’s called
homeostasis;
you can find out more about homeostasis in
Chapter 13
.)
Living things respond to signals in the environment.
If you pop up suddenly and say “Boo!” to a rock, it doesn’t do anything. Pop up and say “Boo!” to a friend or a frog, and you’ll likely see him or it jump. That’s because living things have systems to sense and respond to signals. Many animals sense their environment through their five senses just like you do, but even less familiar organisms, such as plants and bacteria, can sense and respond. (Have you ever seen a houseplant bend and grow toward sunlight? Then you’ve seen one of the responses triggered by a plant cell detecting the presence of light.) Want to know more about the systems that help plants and animals respond to signals? Flip to
Chapter 18
to read all about the human nervous system and
Chapter 21
to discover the details about plant hormones.
Living things transfer energy among themselves and between themselves and their environment.
Living things need a constant supply of energy to grow and maintain order. Organisms such as plants capture light energy from the Sun and use it to build food molecules that contain chemical energy. Then the plants, and other organisms that eat the plants, transfer the chemical energy from the food into cellular processes. As cellular processes occur, they transfer energy back to the environment as heat. (For more on how energy is transferred from one living thing to another, check out
Chapter 11
.)
Living things grow and develop.
You started life as a single cell. That cell divided to form new cells, which divided again. Now your body is made of approximately 100 trillion cells. As your body grew, your cells received signals that told them to change and become special types of cells: skin cells, heart cells, liver cells, brain cells, and so on. Your body developed along a plan, with a head at one end and a “tail” at the other. The DNA in your cells controlled all of these changes as your body developed. (For the scoop on the changes that occur in animal cells as they grow and develop, see
Chapter 19
.)
Living things reproduce.
People make babies, hens make chicks, and plasmodial slime molds make plasmodial slime molds. When organisms reproduce, they pass copies of their DNA onto their offspring, ensuring that the offspring have some of the traits of the parents. (Flip to
Chapter 6
for full details on how cells reproduce and
Chapter 19
for insight into how animals, particularly humans, make more animals.)
Living things have traits that evolved over time.
Birds can fly, but most of their closest relatives — the dinosaurs — couldn’t. The oldest feathers seen in the fossil record are found on a feathered dinosaur called
Anchiornis huxleyi.
Older dinosaur fossils like those of the sauropods show no evidence of feathers
.
From observations like these, scientists can infer that having feathers is a trait that wasn’t always present on Earth; rather, it’s a trait that developed at a certain point in time. So, today’s birds have characteristics that developed through the evolution of their dinosaur ancestors. (Ready to dig into the nitty-gritty details of evolution? See
Chapter 12
.)
Getting savvy about systems
Different types of biologists study living things at different levels of organization, from the very tiny to the very large. Cell biologists might focus on individual cells, or even particular structures inside a cell. Physiologists study whole organisms or focus on a particular system within the body. Ecologists go big and study entire populations of organisms, or the interactions between populations and their environment. Each of these types of scientists chooses which area or system to focus on based on the questions he or she wants to answer.
A system is a group of related parts that work together. As an example, consider your own body. You are a system. You have a boundary (your skin) that keeps all of you separate from the outside world. Within your body, you have many smaller systems like your nervous system or your cardiovascular system that work together so that your whole body functions. To truly understand how one of your organ systems works to help keep you healthy, we need to look not just at that system, but also how it interacts with the other parts of your body.
Systems thinking is an approach that seeks to understand the whole system by looking at the connections between the parts of the system. Systems thinking is a very powerful approach for solving complex problems because it makes people widen their perspective and consider many different components that could contribute to the situation. By taking a wider view and considering the big picture, people are more likely to identify how they can change a system to solve a problem.
For example, let’s say you visit your doctor and find out that your blood pressure is high. Easy fix, right? Just start taking medication to lower your blood pressure. That seemingly quick solution doesn’t look at the causes of the problem, and might have some side effects. Instead, your doctor might start asking you questions to try to figure out how your cardiovascular system (where the blood pressure is detected) is interacting with your other systems, such as
How much salt do you eat? Salt from food enters your digestive system but then ends up in your blood, which can raise your blood pressure.
Are you stressed today? Stress can cause your endocrine system to release hormones that will raise your blood pressure.
How much exercise do you get? Regular exercise uses your musculoskeletal system and strengthens your heart so it doesn’t have to pump as hard, which lowers your blood pressure.
By getting answers to questions like these, your doctor is taking a systems thinking approach to considering your high blood pressure. Based on your answers, your doctor may be able to identify the likely causes of the problem and help you identify the best solution, or combination of solutions (which may include medication), to correct the problem.
Scientists all over the world are using systems thinking as a new way to analyze problems, from understanding human development and aging, to understanding disease, to understanding complex global issues like climate change and public health.
Making Sense of the World through Observations
The true heart of science isn’t a bunch of facts — it’s the method that scientists use to gather those facts. Science is about exploring the natural world, making observations using the five senses, and attempting to make sense of those observations. Scientists, including biologists, use two main approaches when trying to make sense of the natural world:
Discovery science: When scientists seek out and observe living things, they’re engaging in discovery science, studying the natural world and looking for patterns that lead to new, tentative explanations of how things work (these explanations are called hypotheses). If a biologist doesn’t want to disturb an organism’s habitat, he or she may use observation to find out how a certain animal lives in its natural environment. Making useful scientific observations involves writing detailed notes about the routine of the animal for a long period of time (usually years) to be sure that the observations are accurate.
Many of the animals and plants you’re familiar with were first identified during a huge wave of discovery science that took place in the 1800s. Scientists called naturalists traveled the world drawing and describing every new living thing they could find. Discovery science continues today as biologists attempt to identify all the tiniest residents of planet Earth (bacteria and viruses) and explore the oceans to see the strange and fabulous creatures that lurk in its depths.
Hypothesis-based science:
When scientists test their understanding of the world through experimentation, they’re engaging in
hypothesis-based science,
which usually calls for following some variation of a process called the scientific method (see the next section for more on this). Modern biologists are using hypothesis-based science to try and understand many things, including the causes and potential cures of human diseases and how DNA controls the structure and function of living things.
Hypothesis-based science can be a bit more complex than discovery science, which is why we spend the next two sections introducing you to two important elements of hypothesis-based science: scientific method and experiment design.
Introducing the scientific method
The scientific method is basically a plan that scientists follow while performing scientific experiments and writing up the results. It allows experiments to be duplicated and results to be communicated uniformly. Here’s the general process of the scientific method:
First, make observations and come up with questions.
The scientific method starts when scientists notice something and ask questions like “What’s that?” or “How does it work?” just like a child might when he sees something new.
Then form a hypothesis.
Much like Sherlock Holmes, scientists piece together clues to try and come up with the most likely hypothesis (explanation) for a set of observations. This hypothesis represents scientists’ thinking about possible answers to their questions. Say, for example, a marine biologist is exploring some rocks along a beach and finds a new worm-shaped creature he has never seen before. His hypothesis is therefore that the creature is some kind of worm.
One important point about a scientific hypothesis is that it must be testable, or falsifiable. In other words, it has to be an idea that you can support or reject by exploring the situation further using your five senses.
Next, make predictions and design experiments to test the idea(s).
Predictions set up the framework for an experiment to test a hypothesis, and they’re typically written as “if … then” statements. In the preceding worm example, the marine biologist predicts that if the creature is a worm, then its internal structures should look like those in other worms he has studied.
Test the idea(s) through experimentation.
Scientists must design their experiments carefully in order to test just one idea at a time (we explain how to set up a good experiment in the later “Designing experiments” section). As they conduct their experiments, scientists make observations using their five senses and record these observations as their results or data. Continuing with the worm example, the marine biologist tests his hypothesis by dissecting the wormlike creature, examining its internal parts carefully with the assistance of a microscope, and making detailed drawings of its internal structures.
Then make conclusions about the findings.
Scientists interpret the results of their experiments through deductive reasoning, using their specific observations to test their general hypothesis. When making deductive conclusions, scientists consider their original hypothesis and ask whether it could still be true in light of the new information gathered during the experiment. If so, the hypothesis can remain as a possible explanation for how things work. If not, scientists reject the hypothesis and try to come up with an alternate explanation (a new hypothesis) that could explain what they’ve seen. In the earlier worm example, the marine biologist discovers that the internal structures of the wormlike creature look very similar to another type of worm he’s familiar with. He can therefore conclude that the new animal is likely a relative of that other type of worm.
Finally, communicate the conclusions with other scientists.
Communication is a huge part of science. Without it, discoveries can’t be passed on, and old conclusions can’t be tested with new experiments. When scientists complete some work, they write a paper that explains exactly what they did, what they saw, and what they concluded. Then they submit that paper to a scientific journal in their field. Scientists also present their work to other scientists at meetings, including those sponsored by scientific societies. In addition to sponsoring meetings, these societies support their respective disciplines by printing scientific journals and providing assistance to teachers and students in the field.
DISCOVERY SCIENCE OF THE 20TH CENTURY
Although discovery science about the types of plants and animals on Earth had its heyday in the 1800s, discovery science about life on a level that’s too small to see with the naked eye is ongoing. One incredibly important project that employed modern discovery science is the Human Genome Project, which set out to map where each trait is found on the 46 human chromosomes.
Instead of traveling across the oceans to explore the world and catalog living things like the discovery scientists of 200 years ago, scientists from all over the world set out to explore the very tiny, but very complex, landscape of the 46 human chromosomes that contain the collection of all the genes found in humans. Each of the 25,000 genes they located provides information about inherited traits. The traits range from little things, such as whether you can curl your tongue or not, to truly important things, such as whether you have a genetic risk for developing breast cancer or cystic fibrosis. By finding out where genes are located, scientists can turn their attention to using this newfound information to develop hypotheses about cures and gene therapies.
Designing experiments
Any scientific experiment must be repeatable by other scientists so they can confirm or challenge the original scientist’s work. Conclusions from scientific experiments only become part of the scientific knowledge base after they’ve been supported by repeated testing.
When a scientist designs an experiment, she tries to develop a plan that clearly shows the effect or importance of each factor tested by her experiment. Any factor that can be changed in an experiment is called a variable.
Three kinds of variables are especially important to consider when designing experiments:
Experimental variables:
The factor you want to test is an
experimental variable
(also called an
independent variable
).
Responding variables:
The factor you measure is the
responding variable
(also called a
dependent variable
).
Controlled variables:
Any factors that you want to remain the same between the treatments in your experiment are
controlled variables.
Scientific experiments help people answer questions about the natural world. To design an experiment:
Make observations about something you’re interested in and use inductive reasoning to come up with a hypothesis that seems like a good explanation or answer to your question.
Inductive reasoning uses specific observations to generate general principles, like those in a hypothesis.
Think about how to test your hypothesis, creating a prediction about it using an “if … then” statement.
Decide on your experimental treatment, what you’ll measure, and how often you’ll make measurements.
The condition you alter in your experiment is your experimental variable. The changes you measure are your responding variables.
Create two groups for your experiment: an experimental group and a control group.
The experimental group receives the experimental treatment; in other words, you vary one condition that might affect this group. The control group should be as similar as possible to your experimental group, but it shouldn’t receive the experimental treatment.
Set up your experiment, being careful to control all the variables except the experimental variable.
Make your planned measurements and record the quantitative and qualitative data in a notebook.
Quantitative data is numerical data, such as height, weight, and number of individuals who showed a change. It can be analyzed with statistics and presented in graphs. Qualitative data is descriptive data, such as color, health, and happiness. It’s usually presented in paragraphs or tables.
Be sure to date all of your observations.
Analyze your data by comparing the differences between your experimental and control groups.
You can calculate the averages for numerical data and create graphs that illustrate the differences, if any, between your two groups.
Use deductive reasoning to decide whether your experiment supports or rejects your hypothesis and to compare your results with those of other scientists.
Report your results, being sure to explain your original ideas and how you conducted your experiment, and describe your conclusions.
As an example of how you design an experiment, imagine you’re a marathon runner who trains with a group of friends. You wonder whether you and your friends will be able to run marathons faster when you eat pasta the night before the race. To answer your question, follow the scientific method and design an experiment.
Form your hypothesis.
Your hunch is that loading up on pasta will give you the energy you need to run faster the next day. Translate that hunch into a proper hypothesis, which looks something like this: The time it takes to run a marathon is improved by consuming large quantities of carbohydrates prerace.
Treat one group with your experimental variable.
In order to test your hypothesis, convince half of your friends to eat lots of pasta the night before the race. Because the factor you want to test is the effect of eating pasta, pasta consumption is your experimental variable.
Create a control group that doesn’t receive the experimental variable.
You need a comparison group for your experiment, so you convince half of your friends to eat a normal, nonpasta meal the night before the race. For the best results in your experiment, this control group should be as similar as possible to your experimental group so you can be pretty sure that any effect you see is due to the pasta and not some other factor. So, ideally, both groups of your friends are about the same age, same gender, and same fitness level. They’re also eating about the same thing before the race — with the sole exception being the pasta. All the factors that could be different between your two groups (age, gender, fitness, and diet) but that you try to control to keep them the same are your controlled variables.
Measure your responding variable.
Race time is your responding variable because you determine the effect of eating pasta by timing how long it takes each person in your group to run the race. Because scientists carefully record exact measurements from their experiments and present that data in graphs, tables, or charts, you average the race times for your friends in each of the two groups and present the information in a small table. (Race time is a quantitative variable; you could also record qualitative variables like how your friends felt during the race.)
Compare results from your two groups and make your conclusions.
If your pasta-eating friends ran the marathon an average of two minutes faster than your friends who didn’t eat pasta, you may conclude that your hypothesis is supported and that eating pasta does in fact help marathon runners run faster races.
Before you can consider your research complete, you need to look at a few more factors:
Sample size: The number of individuals who receive each treatment in an experiment is your sample size. To make any kind of scientific research valid, the sample size has to be rather large. If you had only four friends participate in your experiment, you’d have to conduct your experiment again on much larger groups of runners before you could proudly proclaim that consuming large quantities of carbohydrates prerace helps marathon runners improve their speed.
Replicates:
The number of times you repeat the entire experiment, or the number of groups you have in each treatment category, are your
replicates.
Suppose you have 60 marathon-running friends and you break them into six groups of 10 runners each. Three groups eat pasta, and three groups don’t, so you have three replicates of each treatment. (Your total sample size is therefore 30 for each treatment.)
Statistical significance:
The mathematical measure of the validity of an experiment is referred to as
statistical significance.
Scientists analyze their data with statistics in order to determine whether the differences between groups are significant. If an experiment is performed repeatedly and the results are consistently similar between repeats and consistently distinct between experimental and control groups, the results are said to be significant. In your experiment, if the race times for your friends were very similar within each group, so that pretty much all of your pasta-eating friends ran faster than your non-pasta-eating friends, then that two-minute difference actually meant something. But what if some pasta-eating friends ran slower than non-pasta-eating friends and one or two really fast friends in the pasta group lowered that group’s overall average? Then you might question whether the two minutes was really significant, or whether your two fastest friends just got put in the pasta group randomly.
Error:
Science is done by people, and people make mistakes, which is why scientists always include a statement of possible sources of error when they report the results of their experiments. Consider the possible errors in your experiment. What if you didn’t specify anything about the content of the normal meals to your non-pasta-eating friends? After the race, you might find out that some of your friends ate large amounts of other sources of carbohydrates, such as rice or bread. Because your hypothesis was about the effect of carbohydrate consumption on marathon running, a few non-pasta-eating friends eating rice or bread would represent a source of error in your experiment.
Whether a scientist is right or wrong isn’t as important as whether he or she sets up an experiment that can be repeated by other scientists who expect to get the same result.
ONE MAN’S ERROR IS ANOTHER MAN’S STARTING POINT
In the early 1900s, a Russian researcher named A.I. Ignatowski fed rabbits a diet of milk and eggs. He found that the rabbits’ aortas developed the same kind of plaques that form in people with atherosclerosis. Ignatowski wasn’t ignorant, but he assumed that the atherosclerosis was caused by the proteins in the milk and eggs. He was wrong.
A younger researcher who was working in the same pathology department at the time, a Russian named Nikolai Anichkov, knew of Ignatowski’s work. Anichkov and some of his colleagues repeated Ignatowski’s study with one small change: They split the rabbits into three different groups. The first group was fed a supplement of muscle fluid, the second group was fed only egg whites, and the third group was fed only egg yolks. Only the yolk-eating rabbits developed plaques in their aortas. The young researchers ran the experiment again; this time they analyzed the atherosclerotic plaques to look for any concentrated chemical substances. In 1913, Anichkov and his colleagues discovered that cholesterol in the egg yolk was responsible for creating plaques in the aorta. Their discovery built on and refined Ignatowski’s original work and added new information to medical science. This is a great example of how science works: Each scientist contributes a piece of the puzzle, but you need the work of many different scientists to reveal the whole picture.
Seeing Science as the Constant Sharing of New Ideas
The knowledge gathered by scientists continues to grow and change slightly all the time. Scientists are continually poking and prodding at ideas, always trying to get closer to “the truth.” They try to keep their minds open to new ideas and remain willing to retest old ideas with new technology. Scientists also encourage argument and debate over ideas because the discussion pushes them to test their ideas and ultimately adds to the strength of scientific knowledge. Following are some of the facts about scientific ideas that illustrate how science is ever-evolving:
Today’s scientists are connected to scientists of the past because new scientific ideas are built upon the foundations of earlier work. For instance, a scientist working in a particular area of biology reads all the scientific publications he can that relate to his work to be sure he has the best understanding possible of what has already been done and what’s already known. That way, he can plan research that will advance the understanding in his field and add new knowledge to the scientific knowledge base.
Some scientific ideas are very old but still applicable today.
Occasionally, new technology enables scientists to test old hypotheses in new ways, leading to new perspectives and changes in ideas. Case in point: Up until the 1970s, scientists looking through microscopes thought only two main types of cells made up living things. When scientists of the ’70s used new technology to compare the genetic code of cells, they realized that living things are actually made up of three main types of cells — two of the types just happen to look the same under a microscope. Of course, old ideas aren’t always proved completely wrong — for example, scientists still recognize the two structural types of cells — but big ideas can shift slightly in the face of new information.
When many lines of research support a particular hypothesis, the hypothesis becomes a scientific theory. A scientific theory is an idea that’s supported by a great deal of evidence and hasn’t been proven false despite repeated tests. Scientific theories don’t change as often as scientific hypotheses due to the significant evidence backing them up, but even scientific theories can shift in light of new evidence. Ideally, scientists always keep an open mind and look at new evidence objectively.
CONFLICTING REPORTS MEAN SCIENCE IS WORKING
Sure, it’s aggravating when the media reports conflicting findings — such as margarine is better for your cholesterol level but it also produces harmful fatty acids that contribute to heart disease — but conflicting news reports are a sign that science is alive and well. For example, when scientists figured out that high cholesterol levels contributed to heart disease, they correctly determined that a product created from vegetable oil rather than animal fat — in other words, margarine rather than butter — was a healthier choice if you were trying to lower your cholesterol level.
But scientists don’t just leave things alone. They keep wondering, questioning, and pondering. They’re curious guys and gals, which is why they kept researching margarine. Recently, they discovered that when margarine breaks down, it releases trans fatty acids, which were found to be harmful to the heart and blood vessels. So, margarine has bad aspects that may outweigh the good. Yes, this can make decisions at the grocery store more confusing, but it can also lead to better health for everyone. Case in point: After the information about trans fatty acids became known, food companies started developing new ways to make margarine and other foods so that they don’t contain trans fatty acids.
Tracking Down Scientific Information
Scientists publish their work in part because scientists in different areas of the world may be trying to answer the same questions and could benefit from seeing how someone else approached the problem. The other part is that if scientists didn’t put their work out there, flaws and all, no one would ever know the work was being done. The sections that follow provide an overview of the different sources scientists use to communicate with each other (and the rest of the world).
Journals: Not just for recording dreams
Hundreds of scientific journals cover every topic and niche imaginable in the fields of biology, chemistry, physics, engineering, and so on. They’re published by numerous organizations, including professional groups, universities or medical centers, and medical and scientific publishing companies. Regardless of their subject matter or where they come from, all scientific journals have one common characteristic: They’re all considered a primary source of scientific information, meaning they contain a full description of the original research written by the original researchers.
Anyone researching a topic, whether he’s a student or a scientist, consults the journals first. They contain the original research papers, which means you can always find the latest information in a specific field in a journal. The research papers are written following the scientific style of an abstract
