Unformatted text preview: Introduction to Biology:
Week one: Biology 102 Themes and Concepts of 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 From its earliest beginnings, biology has wrestled with four
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
how did this diversity arise and how is it continuing? 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. 1: Themes and Concepts of Biology 2: The Process
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 singlecelled 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.
Sensitivity or Response to Stimuli
Organisms respond to diverse stimuli. For example, plants can
grow toward a source of light or respond to touch (Figure 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
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 as diverse as unique heat-resistant Archaea
that live in boiling hot springs to the tongue length of a nectarfeeding 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
Growth and Development
All 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 4) will grow up to
exhibit many of the same characteristics as its parents.
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
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 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
All organisms (such as the California condor shown in Figure
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. 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 7), which contains the
instructions for the functioning of the organism that contains
A flow chart shows the hierarchy of living organisms. From
smallest to largest, this hierarchy includes: 1 An atom, with
protons, neutrons and electrons. 2 Molecules such as the
phospholipid shown, made up of atoms. 3 Organelles, such as Golgi apparatus and nuclei, that exist inside cells. 4 Cells,
such as a red blood cell. 5 Tissues, such as human skin tissue.
6 Organs such as the stomach and intestine make up the
human digestive system, an example of an organ system. 7
Organisms, populations and communities. In a park, each
person is an organism. Together, all the people make up a
population. All the plant and animal species in the park
comprise a community. 8 Ecosystems: The ecosystem of
Central Park in New York includes living organisms and the
environment in which they live. 9 The biosphere: encompasses
all the ecosystems on Earth.
Some cells contain aggregates of macromolecules surrounded
by membranes; these are called organelles. Organelles are
small structures that exist within cells and perform specialized
functions. All living things are made of cells; the cell itself is
the smallest fundamental unit of structure and function in
living organisms. (This requirement is why viruses are not
considered living: they are not made of cells. To make new
viruses, they must invade and hijack a living cell—only then
can they obtain the materials they need to reproduce.) Some
organisms consist of a single cell and others are multicellular.
Cells are classified as prokaryotic or eukaryotic. Prokaryotes
are single-celled organisms that lack organelles surrounded by
a membrane and do not have nuclei surrounded by nuclear
membranes; in contrast, the cells of eukaryotes do have
membrane-bound organelles and nuclei.
In most multicellular organisms, cells combine to make
tissues, which are groups of similar cells carrying out the
same function. Organs are collections of tissues grouped
together based on a common function. Organs are present not
only in animals but also in plants. An organ system is a
higher level of organization that consists of functionally
related organs. For example, vertebrate animals have many
organ systems, such as the circulatory system that transports
blood throughout the body and to and fromthe lungs; it includes organs such as the heart and blood vessels.
Organisms are individual living entities. For example, each
tree in a forest is an organism. Single-celled prokaryotes and
single-celled eukaryotes are also considered organisms and
are typically referred to as microorganisms. Figure 8: Levels of Biological Organization
From an atom to the entire Earth, biology examines all aspects of life.
"Molecule": modification of work by Jane Whitney; "organelles": modification of work by
Louisa Howard; "cells": modification of work by Bruce Wetzel, Harry Schaefer, National
Cancer Institute; "tissue": modification of work by "Kilbad"/Wikimedia Commons;
"organs": modification of work by Mariana Ruiz Villareal, Joaquim Alves Gaspar;
"organisms": modification of work by Peter Dutton; "ecosystem": modification of work
by "gigi4791"/Flickr; "biosphere": modification of work by NASA
All the individuals of a species living within a specific area are collectively called a
population. For example, a forest may include many white pine trees. All of these pine
trees represent the population of white pine trees in this forest. Different populations
may live in the same specific area. For example, the forest with the pine trees includes
populations of flowering plants and also insects and microbial populations. A community
is the set of populations inhabiting a particular area. For instance, all of the trees,
flowers, insects, and other populations in a forest form the forest's community. The
forest itself is an ecosystem. An ecosystem consists of all the living things in a particular
area together with the abiotic, or nonliving, parts of that environment such as nitrogen
in the soil or rainwater. At the highest level of organization (Figure 8), the biosphere is
the collection of all ecosystems, and it represents the zones of life on Earth. It includes
land, water, and portions of the atmosphere. The Diversity of Life
The science of biology is very broad in scope because there is a tremendous diversity of
life on Earth. The source of this diversity is evolution, the process of gradual change
during which new species arise from older species. Evolutionary biologists study the
evolution of living things in everything from the microscopic world to ecosystems.
In the eighteenth century, a scientist named Carl Linnaeus first proposed organizing the
known species of organisms into a hierarchical taxonomy. In this system, species that
are most similar to each other are put together within a grouping known as a genus.
Furthermore, similar genera (the plural of genus) are put together within a family. This
grouping continues until all organisms are collected together into groups at the highest
level. The current taxonomic system now has eight levels in its hierarchy; from lowest to
highest, they are: species, genus, family, order, class, phylum, kingdom, domain. Thus
species are grouped within genera, genera are grouped within families, families are
grouped within orders, and so on (Figure 9). Figure 9: Taxonomic Hierarchy Example: Dog
This diagram shows the levels of taxonomic hierarchy for a dog, from the broadest
category—domain—to the most specific—species.
The highest level, domain, is a relatively new addition to the system since the 1990s.
Scientists now recognize three domains of life, the Eukarya, the Archaea, and the
Bacteria. The domain Eukarya contains organisms that have cells with nuclei. It includes
the kingdoms of fungi, plants, animals, and several kingdoms of protists. The Archaea,
are single-celled organisms without nuclei and include many extremophiles that live in
harsh environments like hot springs. The Bacteria are another quite different group of
single-celled organisms without nuclei (Figure 10). Both the Archaea and the Bacteria
are prokaryotes, an informal name for cells without nuclei. The recognition in the 1990s
that certain "bacteria," now known as the Archaea, were as different genetically and
biochemically from other bacterial cells as they were from eukaryotes, motivated the
recommendation to divide life into three domains. This dramatic change in our
knowledge of the tree of life demonstrates that classifications are not permanent and
will change when new information becomes available.
In addition to the hierarchical taxonomic system, Linnaeus was the first to name
organisms using two unique names, now called the binomial naming system. Before
Linnaeus, the use of common names to refer to organisms caused confusion because
there were regional differences in these common names. Binomial names consist of the
genus name (which is capitalized) and the species name (all lower case).
Both names are set in italics when they are printed. Every species is given a unique
binomial that is recognized the world over, so that a scientist in any location can know
which organism is being referred to. For example, the North American blue jay is known
uniquely as Cyanocitta cristata. Our own species is Homo sapiens. Figure 10: Domain Examples
These images represent different domains. The scanning electron micrograph shows
bacterial cells (a) belong to the domain Bacteria, while the extremophiles (b), seen all
together as colored mats in this hot spring, belong to domain Archaea. Both the
sunflower (c) and lion (d) are part of domain Eukarya.
Credit a: modification of work by Rocky Mountain Laboratories, NIAID, NIH; credit b:
modification of work by Steve Jurvetson; credit c: modification of work by Michael
Arrighi; credit d: modification of work by Frank Vassen Evolution in Action: Carl Woese and the Phylogenetic Tree
The evolutionary relationships of various life forms on Earth can be summarized in a
phylogenetic tree. A phylogenetic tree is a diagram showing the evolutionary
relationships among biological species based on similarities and differences in genetic
or physical traits or both. A phylogenetic tree is composed of branch points, or nodes,
and branches. The internal nodes represent ancestors and are points in evolution when,
based on scientific evidence, an ancestor is thought to have diverged to form two new
species. The length of each branch can be considered as estimates of relative time.
In the past, biologists grouped living organisms into five kingdoms: animals, plants,
fungi, protists, and bacteria. The pioneering work of American microbiologist Carl Woese
in the early 1970s has shown, however, that life on Earth has evolved along three
lineages, now called domains—Bacteria, Archaea, and Eukarya. Woese proposed the
domain as a new taxonomic level and Archaea as a new domain, to reflect the new
phylogenetic tree (Figure 11). Many organisms belonging to the Archaea domain live
under extreme conditions and are called extremophiles. To construct his tree, Woese
used genetic relationships rather than similarities based on morphology (shape). Various
genes were used in phylogenetic studies. Woese's tree was constructed from
comparative sequencing of the genes that are universally distributed, found in some
slightly altered form in every organism, conserved (meaning that these genes have
remained only slightly changed throughout evolution), and of an appropriate length. Figure 11: Phylogenic Tree of Life
This phylogenetic tree was constructed by microbiologist Carl Woese using genetic
relationships. The tree shows the separation of living organisms into three domains:
Bacteria, Archaea, and Eukarya. Bacteria and Archaea are organisms without a nucleus
or other organelles surrounded by a membrane and, therefore, are prokaryotes.
modification of work by Eric Gaba Branches of Biological Study
The scope of biology is broad and therefore contains many branches and subdisciplines.
Biologists may pursue one of those subdisciplines and work in a more focused field. For
instance, molecular biology studies biological processes at the molecular level, including
interactions among molecules such as DNA, RNA, and proteins, as well as the way they
are regulated. Microbiology is the study of the structure and function of microorganisms.
It is quite a broad branch itself, and depending on the subject of study, there are also
microbial physiologists, ecologists, and geneticists, among others.
Another field of biological study, neurobiology, studies the biology of the nervous
system, and although it is considered a branch of biology, it is also recognized as an
interdisciplinary field of study known as neuroscience. Because of its interdisciplinary
nature, this subdiscipline studies different functions of the nervous system using
molecular, cellular, developmental, medical, and computational approaches. Figure 12: Fossil Excavation
Researchers work on excavating dinosaur fossils at a site in Castellón, Spain.
Paleontology, another branch of biology, uses fossils to study life's history (Figure 12).
Zoology and botany are the study of animals and plants, respectively. Biologists can
also specialize as biotechnologists, ecologists, or physiologists, to name just a few
areas. Biotechnologists apply the knowledge of biology to create useful products.
Ecologists study the interactions of organisms in their environments. Physiologists study
the workings of cells, tissues, and organs. This is just a small sample of the many fields
that biologists can pursue. From our own bodies to the world we live in, discoveries in
biology can affect us in very direct and important ways. We depend on these discoveries
for our health, our food sources, and the benefits provided by our ecosystem. Because
of this, knowledge of biology can benefit us in making decisions in our day-to-day lives.
The development of technology in the twentieth century that continues today,
particularly the technology to describe and manipulate the genetic material, DNA, has
transformed biology. This transformation will allow biologists to continue to understand
the history of life in greater detail, how the human body works, our human origins, and
how humans can survive as a species on this planet despite the stresses caused by our
increasing numbers. Biologists continue to decipher huge mysteries about life
suggesting that we have only begun to understand life on the planet, its history, and our
relationship to it. For this and other reasons, the knowledge of biology gained through this textbook and other printed and electronic media should be a benefit in whichever
field you enter. Careers in Action: Forensic Scientist
Forensic science is the application of science to answer questions related to the law.
Biologists as well as chemists and biochemists can be forensic scientists. Forensic
scientists provide scientific evidence for use in courts, and their job involves examining
trace material associated with crimes. Interest in forensic science has increased in the
last few years, possibly because of popular television shows that feature forensic
scientists on the job. Also, the development of molecular techniques and the
establishment of DNA databases have updated the types of work that forensic scientists
can do. Their job activities are primarily related to crimes against people such as
murder, rape, and assault. Their work involves analyzing samples such as hair, blood,
and other body fluids, as well as processing DNA (Figure 13) found in many different
environments and materials. Forensic scientists also analyze other biological evidence
left at crime scenes, such as insect parts or pollen grains. Students who want to pursue
careers in forensic science will most likely be required to take chemistry and biology
courses as well as some intensive math co...
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