BIOL 1003 Chapter Notes - Chapter 1: Archaea, Complex Differential Form, Homeostasis

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22 Nov 2017
Life is a characteristic that distinguishes physical entities that do have biological processes,
such as signaling and self-sustaining processes, from those that do not, either because such
functions have ceased, or because they never had such functions and are classified as
inanimate. Various forms of life exist, such as plants, animals, fungi, protists, archaea, and
bacteria. The criteria can at times be ambiguous and may or may not define viruses, viroids,
or potential artificial life as "living". Biology is the primary science concerned with the study
of life, although many other sciences are involved.
The definition of life is controversial. The current definition is that organisms maintain
homeostasis, are composed of cells, undergo metabolism, can grow, adapt to their
environment, respond to stimuli, and reproduce. However, many other biological definitions
have been proposed, and there are some borderline cases of life, such as viruses.
Throughout history, there have been many attempts to define what is meant by "life" and
many theories on the properties and emergence of living things, such as materialism, the
belief that everything is made out of matter and that life is merely a complex form of it;
hylomorphism, the belief that all things are a combination of matter and form, and the form
of a living thing is its soul; spontaneous generation, the belief that life repeatedly emerges
from non-life; and vitalism, a now largely discredited hypothesis that living organisms
possess a "life force" or "vital spark". Modern definitions are more complex, with input from
a diversity of scientific disciplines. Biophysicists have proposed many definitions based on
chemical systems; there are also some living systems theories, such as the Gaia hypothesis,
the idea that the Earth itself is alive. Another theory is that life is the property of ecological
systems, and yet another is elaborated in complex systems biology, a branch or subfield of
mathematical biology. Abiogenesis describes the natural process of life arising from non-
living matter, such as simple organic compounds. Properties common to all organisms
include the need for certain core chemical elements to sustain biochemical functions
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