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HomeGames & QuizzesHistory & SocietyScience & TechBiographiesAnimals &
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biology
Table of Contents
* Introduction & Top Questions
* Basic concepts of biology
* Biological principles
* Homeostasis
* Unity
* Evolution
* Diversity
* Behaviour and interrelationships
* Continuity
* The study of structure
* Cells and their constituents
* Tissues and organs
* The history of biology
* The early heritage
* Earliest biological records
* Biological practices among Assyrians and Babylonians
* Biological knowledge of Egyptians, Chinese, and Indians
* The Greco-Roman world
* Theories about humankind and the origin of life
* Aristotelian concepts
* Botanical investigations
* Post-Grecian biological studies
* The Arab world and the European Middle Ages
* Arab domination of biology
* Development of botany and zoology
* Revitalization of anatomy
* The Renaissance
* Resurgence of biology
* Advances in botany
* Advances in anatomy
* Advances to the 20th century
* The discovery of the circulation of blood
* The establishment of scientific societies
* The development of the microscope
* Malpighi’s animal and plant studies
* The discovery of “animalcules”
* Swammerdam’s innovative techniques
* Grew’s anatomical studies of plants
* The discovery of cells
* The development of taxonomic principles
* The use of structure for classifying organisms
* Reorganization of groups of organisms
* The development of comparative biological studies
* The study of the origin of life
* Spontaneous generation
* The death of spontaneous generation
* The origin of primordial life
* Biological expeditions
* The development of cell theory
* The theory of evolution
* The study of the reproduction and development of organisms
* Preformation versus epigenesis
* The fertilization process
* The study of heredity
* Pre-Mendelian theories of heredity
* Mendelian laws of heredity
* Elucidation of the hereditary mechanism
* Biology in the 20th and 21st centuries
* Important conceptual and technological developments
* Intradisciplinary and interdisciplinary work
* Changing social and scientific values
* Coping with problems of the future
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Contents
Science Biology Branches of Biology
BIOLOGY
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Written by
Susan Heyner Joshi
Professor of Obstetrics and Gynecology, University of Pennsylvania,
Philadelphia.
Susan Heyner Joshi,
Edna R. Green
Former Head, Science Department, Philadelphia High School for Girls. Coauthor of
Biology.
Edna R. GreenAll
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Last Updated: Jun 12, 2024 • Article History
Table of Contents
biology; microscope
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Key People: George P. Smith Jacques Dubochet Richard Henderson Katherine
Oppenheimer Charles Darwin (Show more)
Related Topics: evolution philosophy of biology taxonomy microbiology omics
(Show more)
On the Web: University of Hawaiʻi Pressbooks - Concepts of Zoology – Hawaiʻi
Edition - Themes and concepts of Biology and Zoology (June 12, 2024) (Show more)
See all related content →
Top Questions
WHAT IS BIOLOGY?
Biology is a branch of science that deals with living organisms and their vital
processes. Biology encompasses diverse fields, including botany, conservation,
ecology, evolution, genetics, marine biology, medicine, microbiology, molecular
biology, physiology, and zoology.
WHY IS BIOLOGY IMPORTANT?
As a field of science, biology helps us understand the living world and the ways
its many species (including humans) function, evolve, and interact. Advances in
medicine, agriculture, biotechnology, and many other areas of biology have
brought improvements in the quality of life. Fields such as genetics and
evolution give insight into the past and can help shape the future, and research
in ecology and conservation inform how we can protect this planet’s precious
biodiversity.
WHERE DO BIOLOGY GRADUATES WORK?
Biology graduates can hold a wide range of jobs, some of which may require
additional education. A person with a degree in biology could work in
agriculture, health care, biotechnology, education, environmental conservation,
research, forensic science, policy, science communication, and many other areas.
biology, study of living things and their vital processes. The field deals with
all the physicochemical aspects of life. The modern tendency toward
cross-disciplinary research and the unification of scientific knowledge and
investigation from different fields has resulted in significant overlap of the
field of biology with other scientific disciplines. Modern principles of other
fields—chemistry, medicine, and physics, for example—are integrated with those
of biology in areas such as biochemistry, biomedicine, and biophysics.
Biology is subdivided into separate branches for convenience of study, though
all the subdivisions are interrelated by basic principles. Thus, while it is
custom to separate the study of plants (botany) from that of animals (zoology),
and the study of the structure of organisms (morphology) from that of function
(physiology), all living things share in common certain biological phenomena—for
example, various means of reproduction, cell division, and the transmission of
genetic material.
Biology is often approached on the basis of levels that deal with fundamental
units of life. At the level of molecular biology, for example, life is regarded
as a manifestation of chemical and energy transformations that occur among the
many chemical constituents that compose an organism. As a result of the
development of increasingly powerful and precise laboratory instruments and
techniques, it is possible to understand and define with high precision and
accuracy not only the ultimate physiochemical organization (ultrastructure) of
the molecules in living matter but also the way living matter reproduces at the
molecular level. Especially crucial to those advances was the rise of genomics
in the late 20th and early 21st centuries.
Cell biology is the study of cells—the fundamental units of structure and
function in living organisms. Cells were first observed in the 17th century,
when the compound microscope was invented. Before that time, the individual
organism was studied as a whole in a field known as organismic biology; that
area of research remains an important component of the biological sciences.
Population biology deals with groups or populations of organisms that inhabit a
given area or region. Included at that level are studies of the roles that
specific kinds of plants and animals play in the complex and self-perpetuating
interrelationships that exist between the living and the nonliving world, as
well as studies of the built-in controls that maintain those relationships
naturally. Those broadly based levels—molecules, cells, whole organisms, and
populations—may be further subdivided for study, giving rise to specializations
such as morphology, taxonomy, biophysics, biochemistry, genetics, epigenetics,
and ecology. A field of biology may be especially concerned with the
investigation of one kind of living thing—for example, the study of birds in
ornithology, the study of fishes in ichthyology, or the study of microorganisms
in microbiology.
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BASIC CONCEPTS OF BIOLOGY
BIOLOGICAL PRINCIPLES
HOMEOSTASIS
The concept of homeostasis—that living things maintain a constant internal
environment—was first suggested in the 19th century by French physiologist
Claude Bernard, who stated that “all the vital mechanisms, varied as they are,
have only one object: that of preserving constant the conditions of life.”
As originally conceived by Bernard, homeostasis applied to the struggle of a
single organism to survive. The concept was later extended to include any
biological system from the cell to the entire biosphere, all the areas of Earth
inhabited by living things.
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UNITY
cells
Animal cells and plant cells contain membrane-bound organelles, including a
distinct nucleus. In contrast, bacterial cells do not contain organelles.(more)
All living organisms, regardless of their uniqueness, have certain biological,
chemical, and physical characteristics in common. All, for example, are composed
of basic units known as cells and of the same chemical substances, which, when
analyzed, exhibit noteworthy similarities, even in such disparate organisms as
bacteria and humans. Furthermore, since the action of any organism is determined
by the manner in which its cells interact and since all cells interact in much
the same way, the basic functioning of all organisms is also similar.
There is not only unity of basic living substance and functioning but also unity
of origin of all living things. According to a theory proposed in 1855 by German
pathologist Rudolf Virchow, “all living cells arise from pre-existing living
cells.” That theory appears to be true for all living things at the present time
under existing environmental conditions. If, however, life originated on Earth
more than once in the past, the fact that all organisms have a sameness of basic
structure, composition, and function would seem to indicate that only one
original type succeeded.
A common origin of life would explain why in humans or bacteria—and in all forms
of life in between—the same chemical substance, deoxyribonucleic acid (DNA), in
the form of genes accounts for the ability of all living matter to replicate
itself exactly and to transmit genetic information from parent to offspring.
Furthermore, the mechanisms for that transmittal follow a pattern that is the
same in all organisms.
Whenever a change in a gene (a mutation) occurs, there is a change of some kind
in the organism that contains the gene. It is this universal phenomenon that
gives rise to the differences (variations) in populations of organisms from
which nature selects for survival those that are best able to cope with changing
conditions in the environment.
EVOLUTION
types of natural selection
Three types of natural selection, showing the effects of each on the
distribution of phenotypes within a population. The downward arrows point to
those phenotypes against which selection acts. Stabilizing selection (left
column) acts against phenotypes at both extremes of the distribution, favouring
the multiplication of intermediate phenotypes. Directional selection (centre
column) acts against only one extreme of phenotypes, causing a shift in
distribution toward the other extreme. Diversifying selection (right column)
acts against intermediate phenotypes, creating a split in distribution toward
each extreme.(more)
In his theory of natural selection, which is discussed in greater detail later,
Charles Darwin suggested that “survival of the fittest” was the basis for
organic evolution (the change of living things with time). Evolution itself is a
biological phenomenon common to all living things, even though it has led to
their differences. Evidence to support the theory of evolution has come
primarily from the fossil record, from comparative studies of structure and
function, from studies of embryological development, and from studies of DNA and
RNA (ribonucleic acid).
DIVERSITY
Despite the basic biological, chemical, and physical similarities found in all
living things, a diversity of life exists not only among and between species but
also within every natural population. The phenomenon of diversity has had a long
history of study because so many of the variations that exist in nature are
visible to the eye. The fact that organisms changed during prehistoric times and
that new variations are constantly evolving can be verified by paleontological
records as well as by breeding experiments in the laboratory. Long after Darwin
assumed that variations existed, biologists discovered that they are caused by a
change in the genetic material (DNA). That change can be a slight alteration in
the sequence of the constituents of DNA (nucleotides), a larger change such as a
structural alteration of a chromosome, or a complete change in the number of
chromosomes. In any case, a change in the genetic material in the reproductive
cells manifests itself as some kind of structural or chemical change in the
offspring. The consequence of such a mutation depends upon the interaction of
the mutant offspring with its environment.
It has been suggested that sexual reproduction became the dominant type of
reproduction among organisms because of its inherent advantage of variability,
which is the mechanism that enables a species to adjust to changing conditions.
New variations are potentially present in genetic differences, but how
preponderant a variation becomes in a gene pool depends upon the number of
offspring the mutants or variants produce (differential reproduction). It is
possible for a genetic novelty (new variation) to spread in time to all members
of a population, especially if the novelty enhances the population’s chances for
survival in the environment in which it exists. Thus, when a species is
introduced into a new habitat, it either adapts to the change by natural
selection or by some other evolutionary mechanism or eventually dies off.
Because each new habitat means new adaptations, habitat changes have been
responsible for the millions of different kinds of species and for the
heterogeneity within each species.
The total number of extant animal and plant species is estimated at between
roughly 5 million and 10 million; about 1.5 million of those species have been
described by scientists. The use of classification as a means of producing some
kind of order out of the staggering number of different types of organisms
appeared as early as the book of Genesis—with references to cattle, beasts,
fowl, creeping things, trees, and so on. The first scientific attempt at
classification, however, is attributed to the Greek philosopher Aristotle, who
tried to establish a system that would indicate the relationship of all things
to each other. He arranged everything along a scale, or “ladder of nature,” with
nonliving things at the bottom; plants were placed below animals, and humankind
was at the top. Other schemes that have been used for grouping species include
large anatomical similarities, such as wings or fins, which indicate a natural
relationship, and also similarities in reproductive structures.
Taxonomy has been based on two major assumptions: one is that similar body
construction can be used as a criterion for a classification grouping; the other
is that, in addition to structural similarities, evolutionary and molecular
relationships between organisms can be used as a means for determining
classification.
BEHAVIOUR AND INTERRELATIONSHIPS
The study of the relationships of living things to each other and to their
environment is known as ecology. Because these interrelationships are so
important to the welfare of Earth and because they can be seriously disrupted by
human activities, ecology has become an important branch of biology.
CONTINUITY
Whether an organism is a human or a bacterium, its ability to reproduce is one
of the most important characteristics of life. Because life comes only from
preexisting life, it is only through reproduction that successive generations
can carry on the properties of a species.
THE STUDY OF STRUCTURE
Living things are defined in terms of the activities or functions that are
missing in nonliving things. The life processes of every organism are carried
out by specific materials assembled in definite structures. Thus, a living thing
can be defined as a system, or structure, that reproduces, changes with its
environment over a period of time, and maintains its individuality by constant
and continuous metabolism.
CELLS AND THEIR CONSTITUENTS
Biologists once depended on the light microscope to study the morphology of
cells found in higher plants and animals. The functioning of cells in
unicellular and in multicellular organisms was then postulated from observation
of the structure; the discovery of the chloroplastids in the cell, for example,
led to the investigation of the process of photosynthesis. With the invention of
the electron microscope, the fine organization of the plastids could be used for
further quantitative studies of the different parts of that process.
Yersinia enterocolitica
Photomicrograph of Gram stain of Yersinia enterocolitica, the causative agent of
yersiniosis.(more)
Qualitative and quantitative analyses in biology make use of a variety of
techniques and approaches to identify and estimate levels of nucleic acids,
proteins, carbohydrates, and other chemical constituents of cells and tissues.
Many such techniques make use of antibodies or probes that bind to specific
molecules within cells and that are tagged with a chemical, commonly a
fluorescent dye, a radioactive isotope, or a biological stain, thereby enabling
or enhancing microscopic visualization or detection of the molecules of
interest.
Chemical labels are powerful means by which biologists can identify, locate, or
trace substances in living matter. Some examples of widely used assays that
incorporate labels include the Gram stain, which is used for the identification
and characterization of bacteria; fluorescence in situ hybridization, which is
used for the detection of specific genetic sequences in chromosomes; and
luciferase assays, which measure bioluminescence produced from
luciferin-luciferase reactions, allowing for the quantification of a wide array
of molecules.
TISSUES AND ORGANS
Early biologists viewed their work as a study of the organism. The organism,
then considered the fundamental unit of life, is still the prime concern of some
modern biologists, and understanding how organisms maintain their internal
environment remains an important part of biological research. To better
understand the physiology of organisms, researchers study the tissues and organs
of which organisms are composed. Key to that work is the ability to maintain and
grow cells in vitro (“in glass”), otherwise known as tissue culture.
Some of the first attempts at tissue culture were made in the late 19th century.
In 1885, German zoologist Wilhelm Roux maintained tissue from a chick embryo in
a salt solution. The first major breakthrough in tissue culture, however, came
in 1907 with the growth of frog nerve cell processes by American zoologist Ross
G. Harrison. Several years later, French researchers Alexis Carrel and Montrose
Burrows had refined Harrison’s methods and introduced the term tissue culture.
Using stringent laboratory techniques, workers have been able to keep cells and
tissues alive under culture conditions for long periods of time. Techniques for
keeping organs alive in preparation for transplants stem from such experiments.
Advances in tissue culture have enabled countless discoveries in biology. For
example, many experiments have been directed toward achieving a deeper
understanding of biological differentiation, particularly of the factors that
control differentiation. Crucial to those studies was the development in the
late 20th century of tissue culture methods that allowed for the growth of
mammalian embryonic stem cells—and ultimately human embryonic stem cells—on
culture plates.
Kara RogersEdna R. Green
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