Introduction to Biology
Biology is the study of living things. It encompasses the cellular
basis of living things, the energy metabolism that underlies the
activities of life, and the genetic basis for inheritance in organisms.
Biology also includes the study of evolutionary relationships among
organisms and the diversity of life on Earth. It considers the biology
of microorganisms, plants, and animals, for example, and it brings
together the structural and functional relationships that underlie
their day-to-day activities. Biology draws on the sciences of
chemistry and physics for its foundations and applies the laws of
these disciplines to living things.
Many subdisciplines and special areas of biology exist, which can be
conveniently divided into practical and theoretical categories. Types
of practical biology include plant breeding, wildlife management,
medical science, and crop production. Theoretical
biology encompasses such disciplines as physiology (the study of
the function of living things), biochemistry (the study of the
chemistry of organisms), taxonomy (classification), ecology (the
study of populations and their interactions with each other and their
environments), and microbiology (the study of microscopic
organisms).
Characteristics of Living Things
Defining a living thing is a difficult proposition, as is defining “life”—
that property possessed by living things. However, a living thing
possesses certain properties that help define what life is.
Complex organization
Living things have a level of complexity and organization not found
in lifeless objects. At its most fundamental level, a living thing is
composed of one or more cells. These units, generally too small to
be seen with the naked eye, are organized into tissues. A tissue is
a series of cells that accomplish a shared function. Tissues, in turn,
form organs, such as the stomach and kidney. A number of organs
working together compose an organ system. An organism is a
complex series of various organ systems.
Metabolism
Living things exhibit a rapid turnover of chemical materials, which is
referred to as metabolism. Metabolism involves exchanges of
chemical matter with the external environment and extensive
transformations of organic matter within the cells of a living
organism. Metabolism generally involves the release or use of
chemical energy. Nonliving things do not display metabolism.
Responsiveness
All living things are able to respond to stimuli in the external
environment. For example, living things respond to changes in light,
heat, sound, and chemical and mechanical contact. To detect
stimuli, organisms have means for receiving information, such as
eyes, ears, and taste buds.
To respond effectively to changes in the environment, an organism
must coordinate its responses. A system of nerves and a number of
chemical regulators called hormones coordinate activities within
an organism. The organism responds to the stimuli by means of a
number of effectors, such as muscles and glands. Energy is
generally used in the process
Organisms change their behavior in response to changes in the surrounding environment. For example,
an organism may move in response to its environment. Responses such as this occur in definite
patterns and make up the behavior of an organism. The behavior is active, not passive; an animal
responding to a stimulus is different from a stone rolling down a hill. Living things
display responsiveness; nonliving things do not.
Growth
Growth requires an organism to take in material from the environment and organize the material into
its own structures. To accomplish growth, an organism expends some of the energy it acquires during
metabolism. An organism has a pattern for accomplishing the building of growth structures.
During growth, a living organism transforms material that is unlike itself into materials that are like it.
A person, for example, digests a meal of meat and vegetables and transforms the chemical material
into more of himself or herself. A nonliving organism does not display this characteristic.
Reproduction
A living thing has the ability to produce copies of itself by the process known as reproduction. These
copies are made while the organism is still living. Among plants and simple animals, reproduction is
often an extension of the growth process. More complex organisms engage in a type of reproduction
called sexual reproduction, in which two parents contribute to the formation of a new individual.
During this process, a new combination of traits can be produced.
Asexual reproduction involves only one parent, and the resulting cells are generally identical to the
parent cell. For example, bacteria grow and quickly reach maturity, after which they split into two
organisms by a process of asexual reproduction called binary fission.
Evolution
Living organisms have the ability to adapt to their environment through the process of evolution.
During evolution, changes occur in populations, and the organisms in the population become better
able to metabolize, respond, and reproduce. They develop abilities to cope with their environment that
their ancestors did not have.
Evolution also results in a greater variety of organisms than existed in previous eras. This proliferation
of populations of organisms is unique to living things.
Ecology
The environment influences the living things that it surrounds. Ecology is the study of relationships
between organisms and their relationships with their environment. Both biotic factors (living things)
and abiotic factors (nonliving things) can alter the environment. Rain and sunlight are non-living
components, for example, that greatly influence the environment. Living things may migrate or
hibernate if the environment becomes difficult to live in.
