Biology -
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.
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.
Unity :
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 :
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).
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