MODULE #1: Biology: The Study of Life
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. The production and use of this energy is called metabolism
(muh tab' uh liz uhm).
Metabolism – The sum total of all processes in an organism which convert energy and matter from outside sources and use that energy and matter to sustain the organism's life functions
Metabolism can be split into two categories: anabolism and catabolism.
Anabolism – The sum total of all processes in an organism which use energy and simple chemical building blocks to produce large chemicals and structures necessary for life
Catabolism – The sum total of all processes in an organism which break down chemicals to produce energy and simple chemical building blocks
Although these definitions might seem hard to understand, think about them this way: when you eat food, your body has to break it down into simple chemicals in order to use it. Once it is broken down, your body will either burn those simple chemicals to produce energy or use them to make larger chemicals. The entire process of breaking the chemicals down and then burning them to produce energy is part of your body's catabolism. Once your body has that energy, it will use some of it to take simple chemicals and build large, complex chemicals that are necessary for your body to work correctly. The process of making those complex chemicals from simple chemicals is part of your body's anabolism. As we progress throughout the course, we will discuss specific examples of anabolism and catabolism, and that will help you better understand the distinction between them. One way to remember these two definitions is to notice that “catabolism” has the same prefix as “catastrophe,” so they both involve things being broken down.
Obviously, then, the energy that an organism gets from its surroundings is important. Where does it come from? Ultimately, 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 a form of energy and that it is 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 (foh' toh sin thuh' sis), convert that energy into food for themselves.
Photosynthesis – The process by which green plants and some other organisms use the energy of sunlight and simple chemicals to produce their own food
We'll be looking at photosynthesis in great detail in a later module. 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 and certain other organisms to convert the energy of sunlight into food. Photosynthesis is a part of anabolism, because the organism takes simple chemicals and converts them into food, which is composed of larger chemicals.
If plants and other photosynthetic organisms 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 (ur' bih vorz).
Herbivores – Organisms that eat only plants
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 (kar' nih vorz).
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 that 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 (ahm nih' vors).
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 past few paragraphs. We took a large number 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 their similarities. In this case, we have taken many 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 biologists have made in understanding God's creation. Biologists have taken an enormous amount of data and have arranged it into many different classification systems. These classification systems allow us to see the similarities and relationships that exist between organisms in creation. Figure 1.1 illustrates the classification system you have just learned.
Click for a video about herbivores, carnivores, and omnivores
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 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 their own food
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 own food from chemicals and 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 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.
Click for an animation about producers, consumers, and decomposers
There are, of course, differences between this classification system (producers, consumers, and decomposers) 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, using this system, 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. Each one tells us different information. For example, if we need to look at the differences that exist among animals, then the first classification scheme is best. Some animals are herbivores (cows, for example), some animals are carnivores (lions, for example), and some animals are omnivores (gorillas, 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 among animals. If, however, we want to study how energy flows from the sun to every creature in creation, the second classification system gives more information about this process.
As a point of terminology, producers are often called autotrophs (aw' toh trohfs), the Greek roots of which literally mean “self-feeder.” Consumers and decomposers, on the other hand, are often called heterotrophs (het' er uh trohfs), which literally means “other-feeder.”
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 throughout the modules in this course. They allow you to reflect on the things you have just read about, cementing the concepts in your mind.