Apologia Biology Sample
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Apologia Biology Sample
Module #1: Biology, The Study Of Life
Introduction
In this course, you're going to take your first detailed look at the science of biology. Biology, the study of life itself, is a vast subject, with many subdisciplines that concentrate on specific aspects of biology. Microbiology, for example, concentrates on those life forms and biological processes that are too small for us to see with our eyes; biochemistry studies the chemical processes that make life possible, and population biology deals with the dynamics of many life forms interacting in a community. Since biology is such a vast field of inquiry, most biologists end up specializing in one of these subdisciplines. Nevertheless, before you can begin to specialize, you need a broad overview of the science itself. That's what this course is designed to give you.
What is Life?
Well, if biology is the study of life, we need to determine what life is. Now to some extent, we all have an idea of what life is. If I were to ask you whether or not a rock is alive, you would easily answer "No!" On the other hand, if I were to ask you whether or not a blade of grass is alive, you would quickly answer "Yes!" Most likely, you can intuitively distinguish between life and non-life.
Even though this is the case, scientists must be a little more deliberate in defining what it means to be alive. Thus, scientists have developed several criteria for life. If something meets all of these criteria, then we can scientifically say that it is alive. If it fails to meet even one of the criteria, it is not alive. These criteria are:
1. All life forms contain deoxyribonucleic acid (DNA).
2. All life forms have a method by which they extract energy from the surroundings and convert it into energy that sustains them.
3. All life forms can sense changes in their surroundings and respond to those changes.
4. All life forms reproduce.
When put together, these criteria define life, as far as science is concerned. Now if you're not sure exactly what each of these criteria mean, don't worry. I will discuss each of them in detail.
DNA and Life
Our first criterion states that all life contains DNA. Now I'm sure you've at least heard about DNA. It is probably, however, still a big mystery to you at this point. Why is DNA so special when it comes to life? Basically, DNA provides the information necessary to take a bunch of lifeless chemicals and turn them into a living system. You see, if I were to analyze an organism and determine every chemical that made up the organism, and if I were then to go into a laboratory and make all of those chemicals and throw them into a big pot, I would not have made something that is alive. I would not have even made something that resembles the organism I studied. Why?
In order to make life, we must take the chemicals that make it up, and we must organize them in a way that will promote the other life functions mentioned in our list of criteria for life. In other words, just the chemicals themselves cannot extract and convert energy (criterion #2), sense and respond to changes (criterion #3), and reproduce (criterion #4). In order to perform those functions, the chemicals must be organized so that they work together in just the right way. Think about it this way: suppose you went to a store and bought a bicycle. The box said "some assembly required." When you got it home, you unpacked the box and piled all of the parts on the floor. At that point, did you have a bicycle? No, of course not. In order to make the bicycle, you had to assemble the pieces in just the right way, according to the instructions. When you got done, all of the parts were in just the right place and worked together with just the right parts. This makes your bike.
In the same way, DNA is the set of instructions that takes the chemicals which make up life and arranges them in just the right way so as to produce a living system. Without this instruction set, the chemicals that make up a life form would be nothing more than a pile of goo. However, directed by the information in DNA, these molecules can work together in just the right way to make a living organism. Now of course, the exact way in which DNA does this is a little complicated. Nevertheless, in an upcoming module, we will spend some time studying DNA and how it works in detail.
Energy Conversion and Life
In order to live, organisms need energy. This is why our second criterion states that all life forms must be able to absorb energy from the surroundings and convert it into a form of energy that will sustain their life functions. This process is called metabolism.
Metabolism - The process by which a living organism takes energy from its surroundings and uses it to sustain itself, develop, and grow
How is metabolism accomplished? It's a long process that actually begins with the sun.
Almost all of the energy on this planet comes from the sun, which bathes the earth with its light. When you take chemistry, you'll learn a lot more about light. For right now, however, all you need to know is that light is pure energy. Thus, the light that comes from the sun is, in fact, the main energy source for all living organisms on our planet. Green plants (and some other things you will learn about later) take this energy and, by a process called photosynthesis, convert that energy into food for themselves.
Photosynthesis - The process by which a plant uses the energy of sunlight and certain chemicals to produce its own food. Oxygen is often a byproduct of photosynthesis.
Now we'll be looking at photosynthesis in great detail towards the end of the course. Thus, if the definition is a little confusing to you, don't worry about it. What you need to know at this point is that photosynthesis allows plants to convert the energy of sunlight into food.
If plants absorb their energy from the sun, where do other life forms get their energy? Well, that depends. Some organisms eat plants. By eating plants, these organisms take in the energy that plants have stored up in their food reserves. Thus, these organisms are indirectly absorbing energy from the sun. They are taking the energy from plants in the form of food, but that food ultimately came from sunlight. Organisms that eat only plants are called herbivores.
Herbivores - Organisms that eat plants exclusively
So you see that even though herbivores don't get their energy directly from sunlight, without sunlight, there would be no plants, and therefore there would be no herbivores.
If an organism does not eat plants, it eats organisms other than plants. These organisms are called carnivores.
Carnivores - Organisms that eat only organisms other than plants
Even though carnivores eat other organisms, their energy ultimately comes from the sun. After all, the organisms that carnivores eat have either eaten plants or have eaten other organisms who have eaten plants. The plants, of course, get their energy from the sun. In the end, then, carnivores also indirectly get their energy from the sun.
Finally, there are organisms that eat both plants and other organisms. We call these omnivores.
Omnivores - Organisms that eat both plants and other organisms
Ultimately, of course, these organisms also get their energy from the sun.
Think about what we just did in the last few paragraphs in this module. We took all of the organisms that live on this earth and placed them into one of three groups: herbivores, carnivores, or omnivores. This kind of exercise is called classification. When we classify organisms, we are taking a great deal of data and trying to organize it into a fairly simple system. In other words, classification is a lot like filing papers. When you file papers, you place them in folders according to similarities that they have. In this case, we have taken all of the organisms on earth and put them into one of three folders based on what they eat. This is one of the most important contributions biology has made in understanding God's creation. Biology has taken an enormous amount of data and has arranged it into many different classification systems. These classification systems allow us to see the similarities and relationships that exist between organisms in God's creation. Figure 1.1 illustrates the classification system you have just learned.
In biology, there are hundreds and hundreds of different ways that we can classify organisms, depending on what kind of data we are trying to organize. For example, the classification system we just talked about groups organisms according to what they eat. Thus, organisms that eat similar things are grouped together. In this way, we learn something about how energy is distributed from the sun to all of the creatures on earth.
This is not, however, the only way we can classify organisms to learn how energy is distributed from the sun to all of the creatures on earth. We could, alternatively, classify organisms according to these groups: producers, consumers, and decomposers.
Producers - Organisms that produce food directly from sunlight
Consumers - Organisms that eat living producers and/or other consumers for food
Decomposers - Organisms that break down the dead remains of other organisms
In this system, plants are producers because they make their food directly from the sun's light. Omnivores, herbivores, and carnivores are all consumers, because they eat producers and other consumers. Certain bacteria and fungi (the plural of "fungus"), organisms we'll learn about in detail later, take the remains of dead organisms and break them down into simple chemicals. Thus, these creatures are the decomposers. Once the decomposers have done their job, the chemicals that remain are once again used by plants to start the process all over again. This, classification scheme, illustrated in Figure 1.2, gives us a nice view of how energy comes to earth from the sun and is distributed to all creatures in God's creation.
There are, of course, differences between this classification (producers, consumers, and decomposers) system and the one you learned previously (omnivores, herbivores, and carnivores). The first difference you should notice between this classification scheme and the one you just studied is that, in this case, we include plants, bacteria, and fungi in the classification. In the previous classification system, we could only classify organisms that ate plants or ate other organisms. There was no grouping in which to put the plants, the bacteria, or the fungi. Does this mean that the second classification system is better than the first? Not really. They each tell us different information. For example, if I need to look at the differences that exist between animals, then the first classification scheme is best. Some animals are herbivores (cows, for example), some animals are carnivores (tigers, for example), and some animals are omnivores (humans, for example). In the second classification system, all animals are consumers. So the second classification system doesn't tell us much about the differences that exist between animals. If, however, we want to study how energy flows from the sun to every creature in Creation, the second classification system is the one to use.
As a point of terminology, producers are often called autotrophs, because they make their own food. Consumers and decomposers, on the other hand, are often called heterotrophs because they have to eat other organisms for food.
Autotrophs - Organisms that are able to make their own food Heterotrophs - Organisms that depend on other organisms for their food
In a little while, these two terms will become very important, so you need to know them.
Before you go on to the next section, answer the "on your own" questions below. These questions will be scattered through out the modules in this course. They allow you to reflect on the things you have just read about, cementing the concepts into your mind.
ON YOUR OWN
1.1 Classify the following organisms as herbivores, carnivores, or omnivores:
a. tigers b. horses c. humans d. sheep
1.2 Classify the following organisms as producers, consumers, or decomposers: a. flowers b. yeast (a fungus) c. lions d. humans
Sensing and Responding to Change
Our third criterion for life is that it senses and responds to change in its surroundings. It is important to realize that in order to meet this criterion, an organism's ability to sense changes is just as important as its ability to respond. After all, even a rock can respond to changes in its environment. If a boulder, for example, is perched on the very edge of a cliff, even a slight change in the wind patterns around the boulder might be enough for it to fall off of the cliff. In this case, the boulder is responding to the changes in its surroundings. The reason a boulder doesn't meet this criterion is that the boulder cannot sense the change.
Living organisms are all equipped with some method of receiving information about their surroundings. Typically, they accomplish this feat with receptors.
Receptors - Special structures or chemicals that allow living organisms to sense the conditions of their surroundings
Your skin, for example, is full of receptors. Some allow you to distinguish between hard and soft substances when you touch them. Other receptors react to hot and cold temperatures. Thus, if you have your hand under a stream of water coming from a water faucet, your receptors react to the temperature of the water. The receptors send information to your brain and you can then react to the temperature. If the water is too hot or too cold, you can remove your hand from the stream to avoid the discomfort.
A living organism's ability to sense and respond to change in its surrounding environment is a critical part of survival, because God's creation is always changing. Weather changes, seasons change, landscape changes, and the community of organisms in a given region changes. As a result, living organisms must be able to sense these changes and adapt, or they would not be able to survive.
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