The characteristics of life By Regina Bailey Biology is the study of life in all of its grandeur, and concerns all life forms, from the very small algae to the very large elephant. But how do we know if something is living? For example, is a virus alive or dead? To answer these questions, biologists have created a set of criteria called the "characteristics of life." Living things include both the visible world of animals, plants, and fungi as well as the invisible world of bacteria and viruses. On a basic level, we can say that life is ordered — organisms have an enormously complex organization. We're all familiar with the intricate systems of the basic unit of life, the cell. Life can "work." No, this doesn't mean all animals are qualified for a job — it means that living creatures can take in energy from the environment. This energy, in the form of food, is transformed to maintain metabolic processes and for survival. Life grows and develops. This means more than just replicating or getting larger in size. Living organisms also have the ability to rebuild and repair themselves when injured. Life can reproduce. Have you ever seen dirt reproduce? I don't think so. Life can only come from other living creatures. Life can respond. Think about the last time you accidentally stubbed your toe. Almost instantly, you flinched back in pain. Life is characterized by this response to stimuli. Finally, life can adapt and respond to the demands placed on it by the environment. There are three basic types of adaptations that can occur in higher organisms. Reversible changes occur as a response to changes in the environment. Let's say you live near sea level and you travel to a mountainous area. You may begin to experience difficulty breathing and an increase in heart rate as a result of the change in altitude. These symptoms go away when you go back down to sea level. Somatic changes occur as a result of prolonged changes in the environment. Using the previous example, if you were to stay in the mountainous area for a long time, you would notice that your heart rate would begin to slow down and you would begin to breathe normally. Somatic changes are also reversible. The final type of adaptation is called genotypic (caused by genetic mutation). These changes take place within the genetic makeup of the organism and are not reversible. An example would be the development of resistance to pesticides by insects and spiders. In summary, life is organized, "works," grows, reproduces, responds to stimuli, and adapts. These characteristics form the basis of the study of biology. Question: A species of fish is found in two ponds. The species in the large pond grows larger than the species in the smaller pond. What is the most logical reason for the size difference in the fish? A. The fish in the large pond have adapted to the larger environment. B. Fewer fish are found in the large pond than in the small pond. C. People avoid trying to catch the fish in the large pond because it is so big. D. The fish in the large pond have more predators, so they have to grow larger.