The Science of Life
This is the most exciting time to be studying biology in the history of the field. The amount of information available about the natural world has exploded in the last 42 years since the construction of the first recombinant DNA molecule. We are now in a position to ask and answer questions that previously were only dreamed of. The 21st century began with the completion of the sequence of the human genome. The largest single project in the history of biology took about 20 years. Yet less than 15 years later, we can sequence an entire genome in a matter of days. This flood of sequence
data and genomic analysis is altering the landscape of biology. These and other discoveries are also moving into the clinic as never before with new tools for diagnostics and treatment.
With robotics, advanced imaging, and analytical techniques, we have tools available that were formerly the stuff of science fiction.
In this text, we attempt to draw a contemporary picture of the science of biology, as well as provide some history and experimental perspective on this exciting time in the discipline. In this introductory chapter, we examine the nature of biology and the
foundations of science in general to put into context the information
presented in the rest of the text.
Biology unifies much of natural science
The study of biology is a point of convergence for the information and tools from all of the natural sciences. Biological systems are the most complex chemical systems on Earth, and their many functions are both determined and constrained by the principles of chemistry and physics. Put another way, no new laws of nature can be gleaned from the study of biology—but that study does illuminate and illustrate the workings of those natural laws.
The intricate chemical workings of cells can be understood
using the tools and principles of chemistry. And every level of biological
organization is governed by the nature of energy transactions
first studied by thermodynamics. Biological systems do not
represent any new forms of matter, and yet they are the most complex
organization of matter known. The complexity of living systems
is made possible by a constant source of energy—the Sun.
The conversion of this radiant energy into organic molecules by
photosynthesis is one of the most beautiful and complex reactions
known in chemistry and physics.
The way we do science is changing to grapple with increasingly difficult modern problems. Science is becoming more interdisciplinary, combining the expertise from a variety of traditional disciplines and emerging fields such as nanotechnology. Biology
is at the heart of this multidisciplinary approach because biological problems often require many different approaches to arrive at solutions. Life defies simple definition In its broadest sense, biology is the study of living things—the science of life. Living things come in an astounding variety of shapes and forms, and biologists study life in many different ways. They live with gorillas, collect fossils, and listen to whales. They read the messages encoded in the long molecules of heredity and count how many times a hummingbird’s wings beat each second. What makes something “alive”? Anyone could deduce that a galloping horse is alive and a car is not, but why? We cannot say,
“If it moves, it’s alive,” because a car can move, and gelatin can wiggle in a bowl. They certainly are not alive. Although we cannot define life with a single simple sentence, we can come up with a series of seven characteristics shared by living systems:
■ Cellular organization. All organisms consist of one or more cells. Often too tiny to see, cells carry out the basic activities of living. Each cell is bounded by a membrane that
separates it from its surroundings.
■ Ordered complexity. All living things are both complex and highly ordered. Your body is composed of many different kinds of cells, each containing many complex molecular structures. Many nonliving things may also be complex, but they do not exhibit this degree of ordered complexity
■ Sensitivity. All organisms respond to stimuli. Plants grow toward a source of light, and the pupils of your eyes dilate when you walk into a dark room.
■ Growth, development, and reproduction. All organisms are capable of growing and reproducing, and they all possess hereditary molecules that are passed to their offspring,
ensuring that the offspring are of the same species.
■ Energy utilization. All organisms take in energy and use it to perform many kinds of work. Every muscle in your body is powered with energy you obtain from your diet.
■ Homeostasis. All organisms maintain relatively constant internal conditions that are different from their environment, a process called homeostasis. For example, your body temperature remains stable despite changes in outside temperatures.
■ Evolutionary adaptation. All organisms interact with other organisms and the nonliving environment in ways that influence their survival, and as a consequence, organisms
evolve adaptations to their environments.
Living systems show hierarchical organization
The organization of the biological world is hierarchical—that is,
each level builds on the level below it:
1. The cellular level. At the cellular level (figure 1.1),
atoms, the fundamental elements of matter, are
joined together into clusters called molecules.
Complex biological molecules are assembled into
tiny structures called organelles within membranebounded
units we call cells. The cell is the basic unit
of life. Many independent organisms are composed
only of single cells. Bacteria are single cells, for
example. All animals and plants, as well as most fungi
and algae, are multicellular—composed of more than
one cell.
2. The organismal level. Cells in complex multicellular
organisms exhibit three levels of organization. The
most basic level is that of tissues, which are groups of
similar cells that act as a functional unit. Tissues, in turn,
are grouped into organs—body structures composed
of several different tissues that act as a structural and
functional unit. Your brain is an organ composed of
nerve cells and a variety of associated tissues that form
protective coverings and contribute blood. At the third
level of organization, organs are grouped into organ
systems. The nervous system, for example, consists of
sensory organs, the brain and spinal cord, and neurons
that convey signals.
3. The populational level. Individual organisms can be categorized into several hierarchical levels within the living world. The most basic of these is the population—a group of organisms of the same species living in the same place. All populations of a particular kind of organism together form a species, its members similar in appearance and able to interbreed. At a higher level of biological organization, a biological community consists of all the populations of different species living
together in one place.
4. The ecosystem level. At the highest tier of biological organization, populations of organisms interact with each other and their physical environment. Together populations and their environment constitute an ecological system, or ecosystem. For example, the
biological community of a mountain meadow interacts with the soil, water, and atmosphere of a mountain ecosystem in many important ways.
5. The biosphere. The entire planet can be thought of as an ecosystem that we call the biosphere. As you move up this hierarchy, the many interactions occurring at lower levels can produce novel properties. These so-called emergent properties may not be predictable. Examining individual cells, for example, gives little hint about the whole animal.
Many weather phenomena, such as hurricanes, are actually emergent
properties of many interacting meteorological variables. It is
because the living world exhibits many emergent properties that it
is difficult to define “life.”
The previous descriptions of the common features and organization
of living systems begins to get at the nature of what it is to
be alive. The rest of this book illustrates and expands on these basic
ideas to try to provide a more complete account of living
systems.
