INTRODUCTION TO
BIOLOGY
Figure 1.1 This NASA image is a composite of several satellite-based views of Earth. To make the whole-Earth image,
NASA scientists combine observations of different parts of the planet. (credi
...
INTRODUCTION TO
BIOLOGY
Figure 1.1 This NASA image is a composite of several satellite-based views of Earth. To make the whole-Earth image,
NASA scientists combine observations of different parts of the planet. (credit: modification of work by NASA)
Chapter Outline
1.1: Themes and Concepts of Biology
1.2: The Process of Science
Introduction
Viewed from space, Earth (Figure 1.1) offers few clues about the diversity of life forms that reside there. The first forms of
life on Earth are thought to have been microorganisms that existed for billions of years before plants and animals appeared.
The mammals, birds, and flowers so familiar to us are all relatively recent, originating 130 to 200 million years ago. Humans
have inhabited this planet for only the last 2.5 million years, and only in the last 200,000 years have humans started looking
like we do today.
1.1 | Themes and Concepts of Biology
By the end of this section, you will be able to:
• Identify and describe the properties of life
• Describe the levels of organization among living things
• List examples of different sub disciplines in biology
Biology is the science that studies life. What exactly is life? This may sound like a silly question with an obvious answer,
but it is not easy to define life. For example, a branch of biology called virology studies viruses, which exhibit some of the
characteristics of living entities but lack others. It turns out that although viruses can attack living organisms, cause diseases,
and even reproduce, they do not meet the criteria that biologists use to define life.
Chapter 1 | Introduction to Biology 5
From its earliest beginnings, biology has wrestled with four questions: What are the shared properties that make something
“alive”? How do those various living things function? When faced with the remarkable diversity of life, how do we organize
the different kinds of organisms so that we can better understand them? And, finally—what biologists ultimately seek to
understand—how did this diversity arise and how is it continuing? As new organisms are discovered every day, biologists
continue to seek answers to these and other questions.
Properties of Life
All groups of living organisms share several key characteristics or functions: order, sensitivity or response to stimuli,
reproduction, adaptation, growth and development, regulation, homeostasis, and energy processing. When viewed together,
these eight characteristics serve to define life.
Order
Organisms are highly organized structures that consist of one or more cells. Even very simple, single-celled organisms are
remarkably complex. Inside each cell, atoms make up molecules. These in turn make up cell components or organelles.
Multicellular organisms, which may consist of millions of individual cells, have an advantage over single-celled organisms
in that their cells can be specialized to perform specific functions, and even sacrificed in certain situations for the good
of the organism as a whole. How these specialized cells come together to form organs such as the heart, lung, or skin in
organisms like the toad shown in Figure 1.2 will be discussed later.
Figure 1.2 A toad represents a highly organized structure consisting of cells, tissues, organs, and organ systems.
(credit: "Ivengo(RUS)"/Wikimedia Commons)
Sensitivity or Response to Stimuli
Organisms respond to diverse stimuli. For example, plants can bend toward a source of light or respond to touch (Figure
1.3). Even tiny bacteria can move toward or away from chemicals (a process called chemotaxis) or light (phototaxis).
Movement toward a stimulus is considered a positive response, while movement away from a stimulus is considered a
negative response.
6 Chapter 1 | Introduction to Biology
This OpenStax book is available for free at http://cnx.org/content/col11487/1.9
Figure 1.3 The leaves of this sensitive plant (Mimosa pudica) will instantly droop and fold when touched. After a few
minutes, the plant returns to its normal state. (credit: Alex Lomas)
Watch this video (http://openstaxcollege.org/l/thigmonasty) to see how the sensitive plant responds to a touch stimulus.
Reproduction
Single-celled organisms reproduce by first duplicating their DNA, which is the genetic material, and then dividing it equally
as the cell prepares to divide to form two new cells. Many multicellular organisms (those made up of more than one cell)
produce specialized reproductive cells that will form new individuals. When reproduction occurs, DNA containing genes is
passed along to an organism’s offspring. These genes are the reason that the offspring will belong to the same species and
will have characteristics similar to the parent, such as fur color and blood type.
Adaptation
All living organisms exhibit a “fit” to their environment. Biologists refer to this fit as adaptation and it is a consequence
of evolution by natural selection, which operates in every lineage of reproducing organisms. Examples of adaptations are
diverse and unique, from heat-resistant Archaea that live in boiling hot springs to the tongue length of a nectar-feeding moth
that matches the size of the flower from which it feeds. All adaptations enhance the reproductive potential of the individual
exhibiting them, including their ability to survive to reproduce. Adaptations are not constant. As an environment changes,
natural selection causes the characteristics of the individuals in a population to track those changes.
Growth and Development
Organisms grow and develop according to specific instructions coded for by their genes. These genes provide instructions
that will direct cellular growth and development, ensuring that a species’ young (Figure 1.4) will grow up to exhibit many
of the same characteristics as its parents.
Chapter 1 | Introduction to Biology 7
Figure 1.4 Although no two look alike, these kittens have inherited genes from both parents and share many of the
same characteristics. (credit: Pieter & Renée Lanser)
Regulation
Even the smallest organisms are complex and require multiple regulatory mechanisms to coordinate internal functions,
such as the transport of nutrients, response to stimuli, and coping with environmental stresses. For example, organ systems
such as the digestive or circulatory systems perform specific functions like carrying oxygen throughout the body, removing
wastes, delivering nutrients to every cell, and cooling the body.
Homeostasis
To function properly, cells require appropriate conditions such as proper temperature, pH, and concentrations of diverse
chemicals. These conditions may, however, change from one moment to the next. Organisms are able to maintain internal
conditions within a narrow range almost constantly, despite environmental changes, through a process called homeostasis
or “steady state”—the ability of an organism to maintain constant internal conditions. For example, many organisms
regulate their body temperature in a process known as thermoregulation. Organisms that live in cold climates, such as the
polar bear (Figure 1.5), have body structures that help them withstand low temperatures and conserve body heat. In hot
climates, organisms have methods (such as perspiration in humans or panting in dogs) that help them to shed excess body
heat.
Figure 1.5 Polar bears and other mammals living in ice-covered regions maintain their body temperature by generating
heat and reducing heat loss through thick fur and a dense layer of fat under their skin. (credit: "longhorndave"/Flickr)
Energy Processing
All organisms (such as the California condor shown in Figure 1.6) use a source of energy for their metabolic activities.
Some organisms capture energy from the Sun and convert it into chemical energy in food; others use chemical energy from
molecules they take in.
8 Chapter 1 | Introduction to Biology
This OpenStax book is available for free at http://cnx.org/content/col11487/1.9
Figure 1.6 A lot of energy is required for a California condor to fly. Chemical energy derived from food is used to power
flight. California condors are an endangered species; scientists have strived to place a wing tag on each bird to help
them identify and locate each individual bird. (credit: Pacific Southwest Region U.S. Fish and Wildlife)
Levels of Organization of Living Things
Living things are highly organized and structured, following a hierarchy on a scale from small to large. The atom is the
smallest and most fundamental unit of matter. It consists of a nucleus surrounded by electrons. Atoms form molecules. A
molecule is a chemical structure consisting of at least two atoms held together by a chemical bond. Many molecules that
are biologically important are macromolecules, large molecules that are typically formed by combining smaller units called
monomers. An example of a macromolecule is deoxyribonucleic acid (DNA) (Figure 1.7), which contains the instructions
for the functioning of the organism that contains it.
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