1.1: Characteristics of Life
Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, distribution, and taxonomy. The field's scope is extensive and divided into several specialized disciplines, such as anatomy, physiology, ethology, genetics, and many more. All living things share a few key traits, including cellular organization, heritable genetic material and the ability to adapt/evolve, metabolism to regulate energy needs, the ability to interact with the environment, maintain homeostasis, reproduce, and the ability to grow and change.
The Complexity of Life
Despite its complexity, life is organized and structured. The cell theory in biology states that all living organisms are composed of one or more cells. The cell is the basic unit of life, and all cells arise from previously existing cells. Even single-celled organisms, such as bacteria, have structures that allow them to carry out essential functions, such as interacting with the environment and carrying out chemical reactions that maintain life or metabolism. In multicellular organisms, cells work together to form tissues, organs, organ systems, and entire organisms. This hierarchical organization can extend into populations, communities, ecosystems, and the biosphere.
Genetics and Adaptation
An organism's genetic material, the biological "blueprints" encoded in its DNA, is passed down to its offspring. Throughout several generations, the genetic material is shaped by the biotic (living) and abiotic (non-living) environment. This process is called adaptation. Offspring of well-adapted parents have a high likelihood of surviving in conditions similar to those in which their parents lived. Natural selection is the process in which inherited traits increase survival and reproduction. Natural selection is the central mechanism of evolution. For example, some kangaroo rats live in hot and dry areas with little rainfall. To avoid the blistering heat and conserve water, they burrow into the soil where it is colder and lower their metabolic rate to slow down evaporation. In this way, the kangaroo rat's genetics—encoding this behavior and passed down through generations—enables the animal to survive such extreme environmental conditions.
Organisms must also be able to interact successfully with their environment. This includes navigating the world around them in search of resources or potential mates and regulating their internal environments. Homeostasis is the ability of an organism to keep steady internal conditions. For example, humans maintain a constant body temperature. If they get cold, they shiver; if it's too hot, they sweat. Living things also carry out metabolism—the chemical processes that regulate energy needs. For instance, plants convert sunlight into sugar and store chemical energy in adenosine triphosphate.
Building Upwards from Basic Tenets
While "What is biology?" and "What is life" may seem like basic questions, they are essential to understand and are prerequisites to asking more complicated questions. For example, without understanding the basic tenets of life—such as how cells divide and replicate—it would be difficult to investigate what causes cancer. This knowledge also allows scientists to develop the required tools and methods to study biological processes.