Is It Alive? (Part Two – Metabolism)

It Sounds Familiar…

We’ve probably heard this word used mainly in fitness and diet-based conversations. I’ve heard many people say they can eat anything at anytime and not gain weight because they have a “fast” metabolism. I’ve also heard people say they can simply look at a candy bar and gain weight because they have a very “slow” metabolism. So just what is this metabolism thing and how is it a characteristic of life?

So What Is It?

Metabolism is the process of using energy to both break apart and make molecules. In other words, it takes energy to digest the food you eat. This process is called catabolism – using some of the body’s energy to break down the food we eat (read: food coma).

On the other hand, it also takes energy to make or build molecules, such as protein in muscle tissue. This is called anabolism. (Think anabolic steroids – building muscle mass). Last time you worked out, did you sweat, grunt or strain? Congratulations, you’re alive!

All biological organisms have an active metabolism, that is, they all use energy. We couldn’t live without it. Even the smallest organisms (bacteria) utilize energy to eat and also to build certain biomolecules, such as proteins and carbohydrates.

Where It All Starts

Where does all this energy come from to “power” life on Earth? Ultimately, the sun. The plants use the sun’s energy to make a special sugar molecule called glucose. This process is called photosynthesis. Animals then eat the plants (the herbivores) while other animals (called carnivores) eat the herbivores. So we can see how the energy contained in the food we order from McDonald’s (burgers and fries) ultimately came from a source about 93 million miles away!

So What About…

“Well what about solar panels?” you ask, “They use the sun’s energy also.” True. While technology like solar panels also use the sun’s energy, they don’t have a biological metabolism because they don’t make or synthesize biomolecules from the energy they consume. The solar panels simply store the energy and convert it into a human-friendly form: electricity.

What about your gas-guzzling vehicle? Or have you ever had to charge your mobile phone? These objects use energy, but they don’t have a metabolism. Your vehicle breaks down the gasoline through combustion (burning), but it doesn’t make any large molecules in return. Its “metabolism” is a “one-way street.” As for your mobile phone, well, those things are just plain magic; I don’t suppose anyone knows how those things really work…simply amazing…

So while there may be objects in our world that have the ability to use energy, they may not be considered alive because the object must have most, if not all, of the seven characteristics of life. Stay tuned for the next articles as we continue to answer the question, “Is It Alive?”

Articles in this series, “Is It Alive?”

• Part 1 – Organization
• Part 2 – Metabolism
• Part 3 – Homeostasis
• Part 4 – Response
• Part 5 – Growth
• Part 6 – Reproduction
• Part 7 – Adaptation

Please visit my BioBlog @ SantiagoRLopez.com for other biology-related material.