Study Guide

Biology Study Guide

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    Biology Introduction

  • Introduction

    biology Introduction Video

    We can see it all now: high school biology class. We are picturing uncomfortable metal stools; lectures on lab safety; NOVA videos; those giant, take-over-your-entire-face safety goggles that are always scratched beyond belief. They suck on your eyeballs and oh, lest we forget about the might-as-well-be-permanent goggle marks you will be sporting for the PE class that comes right after bio lab. Luckily for you, we don't have any of that stuff. OK, there may be a few NOVA videos. However, we threw in some Bill Nye, too, just to even things out.

    Welcome to Shmoop's Biology 101, your virtual home for all things vegetable, animal, and mineral. Before we jump into the beastin' world of Biology, let's go through some pros and cons of the online version, as opposed to the real thing.


    • You will not need to shower eight times to get the smell of formaldehyde out of your hair after dissecting those frogs.
    • You will not need to worry about shattering a beaker and going into DEFCON 1 as your teacher assembles a perimeter around the broken glass.
    • You will not be accidentally electrocuted while trying to plug in a microscope after one of your idiot classmates breaks off some metal in the socket. (Trust us, it happens. And it hurts.)
    • You can eat while studying. We don't know about your school, but that was generally frowned upon in our biology classes.
    • You can wear your pajamas! Or, nothing at all, if you really want to. Just remember to turn off your webcams first. We know that bizness isn't allowed at your regular, old, non-virtual high school.  
    • No cleaning the mess afterward. Score.


    • We can't replicate that oh-so-unique biology classroom smell. Actually, maybe that's a pro.
    • There are no opportunities for sparkly vampire lab partners, à la Twilight. Maybe study with a buddy to stave off those feelings of loss. What will you do without your lover with the creepy stare and an apparent anger management problem?
    • No killing things. This should also be a pro. Who put this here?
    • No touching dead things. Again, probably a pro. Rock on, Internet.
    • We cannot replicate the truly enlightening experience of having a semi-narcoleptic lab partner. All we have to say is, keep away all sharp objects.
    • No microscopes. We are not gonna lie. Microscopes are beyond awesome.
    • No furry bunnies, lamp-lovin' lizards, or suicidal fish that have nightmares…we mean, pleasant dreams…about students poking them, shouting at them, and forgetting to feed them. PetCo is just down the street.
    • No field trips to the zoo. Another legit con. Request a zoo field trip by emailing

    Well, that settles it. Bunch of pros and…one or two cons. Looks like you are stuck using Shmoop for all of your biology needs. Although, there is nothing like a good squirt of frog juice right in your left goggle...

  • What is Biology?

    Biology is the study of life. As if you haven’t heard that line a hundred times before. But, Biology doesn’t stop there; you will find an amazing variety of topics and ideas on Planet Bio. Here is a little taste of what we will be investigating:

    • What, exactly, does it mean to be alive? Personally, we would have a hard time imagining a life where we didn't have the ability to kick virtual butt on our PS3s, but peonies and pandas might disagree.
    • How do living things "work"? What makes them tick? Or chirp, or bark, or bray? (Sorry.)
    • How do living things reproduce and grow? Awkward lesson on the birds and the bees, coming right up…
    • How do living things interact with each other? Do they friend each other and like each other's statuses? Probably not.
    • Where did life come from, and how has it changed over time? We're talking about more than just the rise and fall and rise again of parachute pants.

    From the beginning (where else would this bad boy start?)…

  • Life is Complex

    What is Life?

    Nope, you are not in philosophy class. Even though "What is life?" is the kind of mind-draining question we could spend days talking about over espresso and pain au chocolot, a biologist would tell you that all living things—organisms, creatures, beasties, take your pick—have five characteristics in common. That's right; you are not officially alive if you cannot do the five things on this and the following four pages. Hand-eye coordination is not among them. You can breathe again.

    Living things are complex and organized.

    Living creatures are well-oiled machines. Despite the nicely packaged outward appearance, living creatures have various different levels of organization that are extremely complex.

    Starting at the lowest level of organization, subatomic particles—such as protons, neutrons, and electrons—make up atoms. Atoms, in turn, can combine with other atoms to form a dizzying variety of molecules. Molecules get together and form cellular structures, including organelles, or as we like to call them, "mini organs."

    Many different organelles work together inside a cell. The cell is the most basic functional unit of life.

    In a multicellular organism, a group of cells that all share the same tasks is called a tissue, and one or more tissues form an organ. Organs are organized into organ systems, and a whole organism has many organ systems working together to get things done.

    However, a single-celled individual lacks tissues, organs, and organ systems, but it still has the same levels of organization below the cellular level: protons, neutrons, electrons, atoms, and molecules.

    Many individuals living in the same place form a population, and all the interbreeding populations of a certain kind of living organism make up a species. When populations of different species interact, they form a community…and have lots of parties.

    An ecosystem includes all the living organisms in a certain area in addition to the nonliving parts of their environment, which usually includes many different communities. Finally, the highest level of organization is the biosphere—encompassing all the living things on Earth. Phew.

  • Life uses Energy

    Living things gain and use matter and energy. Like, "Red Bull gives you wings"?

    We have established that all living critters have several levels of organization. Since you continually reorganize your impeccably kept biology notebook as if you were a squirrel hopped up on caffeine, we know you have no doubt that maintaining organization requires energy—lots and lots of energy.

    Think of all the calendars, day planners, and lists that you have made in your lifetime (or haven't made, if you aren't the planning type). Organization is hard! Cells acquire matter and energy to not only maintain their structures and functions but also to grow and reproduce. Bow chicka wow wow. The matter and energy acquired by a living organism are used in chemical reactions, and the sum of all these chemical reactions in one living organism is referred to as its metabolism.

    Living organisms get their matter and energy from the environment. Depending on the type of organism, matter in the form of nutrients can be "sipped" from air, soil, water, and/or food. Energy, on the other hand, is created either by photosynthesis or by extracting it from other living organisms. That would explain why little ol' humans like us feel mighty sluggish after going a few hours without eating.

    Some living creatures—like plants and many unicellular organisms—perform photosynthesis: they convert light from the sun directly into usable energy. Other living things—like fungi, non-photosynthetic unicellular organisms, and animals—eat other living things. Not very neighborly, but hey, it’s a dog-eat-dog-food world…

  • Life is Maintained

    Living things maintain a relatively constant condition, called homeostasis.

    Cells are very picky, and constancy is key to proper functioning for these little guys. When thinking about the need for constancy, consider what might happen if you stopped brushing your teeth or showering every day. Your life would probably be thrown into chaos. You'd lose friends (yeah, as much as you'd like to believe that it's your personality that keeps 'em coming back, personal hygiene is pretty important). You'd get cavities and weird diseases. You might even be unlucky enough to develop what we call "Pig-Pen-itis," a disorder that curses you with perpetually orbiting dust clouds and stink lines. Nobody wants that, so our bodies try really hard to keep us in homeostasis.

    The chemical processes that take place inside cells are highly sensitive to surrounding conditions. This is because variations in temperature, pH, and concentrations of various substances, like salt, can affect the function of enzymes. Enzymes are the VIPs, or "very important proteins," of the protein world. They catalyze, or set in motion, chemical reactions, processes where one set of chemicals becomes a different set of chemicals. Enzymes can alter the rates at which all those reactions occur. In rare circumstances, enzymes may stop working, which is majorly bad news for the cell that they live in.

    As important as constancy is, the reality is that a cell’s environment can change quickly. Just think about the changes your body encounters when you plunge into the cold ocean after basking in the hot sun, or when you wipe out on your surfboard and accidentally swallow a mouthful of salty water. If your cells didn’t have a way to cope with these situations, you’d be toast. Soggy, salty toast. Fortunately, living organisms have all kinds of strategies up their figurative sleeves to maintain homeostasis.

    Temperature regulation is a great example. Endothermic organisms, or those who can generate heat internally, use their metabolisms to keep body temperatures constant. Most mammals and birds are endothermic. When the ambient (environmental) temperature is a little too cold, endotherms increase their metabolism, which produces more heat. On the other hand, when the ambient temperature becomes too hot, many animals release sweat to help cool themselves. Under most environmental conditions, the body temperature in these animals remains almost perfectly constant. Nice work, endotherms.

  • Life Reproduces

    Living things reproduce. Scandalous.

    On to reproduction! Don't worry; we won't get too cringeworthy on you. Reproduction is important in biology because, well, it’s the key to the success of any species. Right? Take a deep breath, because we're going to say this once and then never mention it again: Where would you be if your parents hadn't done some propagating nine months before you were born? Ew.

    Ask most people to define success, and you are likely to hear some recurring themes: fame, fortune, making a difference, retiring by age 35 to a beachside paradise with an unending supply of delicious tropical fruits. You get the picture. But, from a purely biological standpoint, the only thing you really need to do is procreate.

    Reproduction is essential for the perpetuation of life, and it is one of the traits that all living organisms under the sun share. Living organisms pass their genetic material from generation to generation, and the genetic material we are talking about here is deoxyribonucleic acid, mercifully called DNA for short. DNA resides in the nucleus of the cell and contains the genetic blueprint that controls all of a cell’s activities.

  • Life Evolves

    Living things change over time; this process is called evolution.

    Any single living organism, over the course of its life, will experience changes. For humans, unfortunately timed voice cracking is probably the most embarrassing among them. But this individual development is not to be confused with changes in populations of living things over geologic (read: long) periods.

    Because of the genetic variation inherent in all populations, over time traits will change, and future generations of a population may look, behave, and function differently from their ancestors. Who knows? Maybe in a thousand years, everyone will have six fingers on their right hands. Some species will go extinct. New species will appear. This process is called evolution, and the most important concept in evolution is natural selection.

    Charles Darwin, who had a beard that could give Dumbledore a run for his money, and his colleague Alfred Russel Wallace first proposed natural selection in 1859. Darwin—or Charlie, as we like to call him—usually gets more credit because, well, he thought of it first. You’ll read a lot more later about natural selection and other mechanisms of evolution, but in a nutshell, natural selection is based on four main points:

    1. In most species, more offspring are produced than will ultimately survive and reproduce. Sad, but true.
    2. Variation exists within a species. Human variation is obvious to us, but we tend not to realize that populations of other organisms vary, too. Variation exists in every living species, from skunks to amoebas to lima beans.
    3. Taking points 1 and 2 a step further, variation contributes to who survives and who doesn’t. In other words, those who succeed in surviving and reproducing themselves are successful in part because of the specific traits they possess.
    4. Some of the traits that vary and contribute to success are heritable, meaning they can be passed on from generation to generation. How many times does Harry Potter hear that he has his mother’s eyes?

    Putting this all together, here’s the bottom line: not everyone is going to make it, and of those who do, not everyone will be equally successful, or "reproductively prolific." Since there is variation in the population, some individuals will have traits that make them better able to survive and reproduce. Maybe they’re faster at escaping from predators, keener at sniffing out food, or more tolerant of harsh conditions. These individuals will be the ones that pass their traits along to their offspring.

    Over time, whoever can produce the most offspring that live to reproduce will be the one whose traits prevail in a population. Natural selection is the idea that traits are selected based on the benefit they provide to their possessor; that benefit, in turn, depends on environmental conditions, like predators, disease, resource availability, climate, and so on. The possibilities are endless.

  • Major Biology Themes

    Not surprisingly, several of the points introduced earlier as characteristics of life are also big recurring themes in biology. Who would have guessed, right? It's not like we planned it this way or anything. *shifty eyes*

    What exactly do we mean by "big recurring themes"? Well, you will see all of these ideas over and over again, in a bunch of different contexts and situations. Let's get cracking.

    1. Evolution

    Evolution is an important theme in biology. If you go looking for it, you'll be able to find an aspect of every living creature that is a product of evolution. How did life get to be the way that it is? Evolution, that's how.

    2. Levels of organization

    How do systems, processes, and events at one level of organization affect other levels? Are units at one level just the sum of units at other levels, or are there emergent properties unique to certain levels? As you may have guessed by our strategic bolding, the latter choice is the answer.

    3. Regulation

    Let’s face it: life is a control freak. Everything is regulated, and when regulation fails, the results are generally not good. How does regulation work at the different levels of organization, such as molecules, organs, and ecosystems? That's the question we ask when considering this theme.

    4. Structure and function

    How do biological structures relate to the functions they perform? Is a specific structure ideal or optimal for that function? If not, how might this less-than-optimal structure be explained by evolution?

    5. Unity and diversity

    Certain structures and processes may be common to many or all life forms, but nature has modified them in diverse ways, resulting in a tremendous range of variation.

    This list of themes isn’t complete yet, and as you bask in your newfound, undying love of biology, you will no doubt come up with themes of your own. Try to keep these ideas in the back of your mind—preferably forever, but if that’s not possible then at least as long as you’re learning biology. They will enable you to keep everything you learn in perspective, so that you can see how all the little tidbits of information fit into the big picture. That’s what biology is all about: little, teensy tiny tidbits and how they fit into a bigger picture. Oh, and organization, organization, and more organization.

  • The Scientific Method

    Who are biologists, and how do they study biology? Contrary to popular belief, biologists are not boring, soulless, and socially awkward people wearing white lab coats and crooning to baby lizards. Well, not all of them, anyway…

    In reality, biologists are as diverse as the organisms they study, and range from lab-dwelling DNA amplifiers and tree-swinging insect collectors to SCUBA-diving underwater cave explorers. We'd like to apply for that job. Please? We swear, we would totally rock at it. And we're qualified because we know what SCUBA stands for. That's totally all we need to know to be underwater cave explorers, right? Biologists can be found in numerous habitats, including universities, governments, pharmaceutical labs, zoos, medical facilities, national parks, and museums, to name a few.

    Since biology is a science (shocker), biologists use the scientific method to formulate and test questions about the natural world. Oh yes, Shmoopers, believe it or not, there is a process for figuring things out in biology. The scientific method is usually presented as a linear process:

    Observation leads to a hypothesis, which is tested by an experiment, which yields a conclusion.

    But, as neat, orderly, and easy as this seems, this is not usually how science plays out. The scientific method is a tremendously complex and creative process that involves asking questions, making observations, doing experiments, and soliciting feedback. Scientists are constantly revising their questions, hypotheses, and experiments as new information is gathered. Doesn't that sound like fun?

    All of you can read more about the scientific method here.

  • Why Should I Care?

    Biology affects your life in lots of ways. For instance, understanding how your organs and organ systems work together can help you maintain a healthy lifestyle. Learning how cells communicate with each other, how cellular processes are controlled and coordinated, and what regulates cell growth can help you understand many common diseases and identify the ways that drug therapies work. A solid appreciation for the inter-connectedness of life at the population, community, and ecosystem levels can help you learn more about the environment and how you alter it.

    Ultimately, if you become knowledgeable about the science that underlies disease, environmental issues, and hot-button research initiatives, like stem cell research, you will be a more thoughtful and valuable contributor to debates that surround how this research is used and understood. Biology isn’t just for biologists: it’s useful—even fundamental—to everyone living on this lovely planet.

    In addition to these practical benefits, you may find that once you know biology, you better appreciate just how beautiful, complex, and amazing the natural world is. In this sense, biology is not so different from art or poetry. A painter may appreciate a beautiful flower by painting it; a poet may garner the same appreciation by writing about it; and a biologist appreciates the flower by understanding how it works and how it came to be, even if that seems a little nerdy.

    And, if these aren’t compelling enough reasons to study biology, consider the variety of smart, unique pickup lines that are inspired by biology:

    "Nice genes."

    "You are the light pulling my cotyledons through the soil of life."

    "You increase my metabolism like oxygen to a facultative anaerobe."

    Try those on your crush. Who says scientists can’t be romantics?

    A final word

    When the going gets tough, remember: compared to the rest of the animal kingdom, you have a huge brain to body size ratio. Don't let evolution down. Use that gray matter to its full potential. You got this.

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