Life?

Here all aspects of Philosophical Alchemy can be discussed for example, the works of Carl Gustav Jung, Helena Petrovna Blavatsky, Mircea Eliade, Socrates, Plato. The method, discipline, and school of thought of Taoism, Kabbalah, Gnosticism etc...

Life?

Postby Ghislain » Tue Sep 24, 2013 7:08 pm

The purpose of this topic is to attempt a summary of life. As you read the introduction it will
immediately become clear that this endeavour is no mean feat. It uses extracts from a plethora of
internet sites that discuss in much greater depth the matters discussed here; where possible links
have been introduced.

How to define "life" is a sweeping question that affects whole branches of biology, biochemistry,
genetics, and ultimately the search for life elsewhere in the universe.

When asking the question, “what is life”, a biologist might give a dramatically different answer than
that given by a theoretical physicist, or someone of a religious persuasion.

Some initial agreement seems possible as living things:

    • Tend to be complex and highly organized.
    • Have the ability to take in energy from the environment and transform it for growth and reproduction.
    • Tend to respond, i.e. their stimulation fosters a reaction-like motion, recoil, and in advanced forms, learning
    • Are reproductive, as some kind of copying is needed for evolution to take hold through a population's mutation and natural selection.
    • Need to be consumers, since growth includes changing biomass, creating new individuals, and the shedding of waste.
    • Normally have an environment outside of which they cannot survive.

Until the 20th century, most biologists considered all living things to be classifiable as either
a plant or an animal, but by the 1950s and 1960s, most biologists came to the realization that
this system failed to accommodate the fungi, protists, and bacteria.

On the macroscopic level it is quite easy to see the distinction between a plant and an animal, but on
a microscopic level this situation breaks down. Not only are there single-celled organisms that
sometimes act like plants and sometimes like animals (Euglena for example photosynthesise food
from sunlight but also can feed by consuming organic matter like an animal). Then there are bacteria
and blue-green algae, which differ structurally from higher organisms far more than plants differ
from animals.

An archetypal change was required and by the 1970s, a system of Five Kingdoms, hypothesis
established by Robert Whittaker in 1969, had come to be accepted as the model by which all living
things could be classified.

The Five Kingdoms


Image


Animalia
Animals are the most complex organisms on Earth. Animals are multi-celled organisms, eat food for
survival, and have nervous systems. They are divided into vertebrates and invertebrates and include
mammals, amphibians, reptiles, birds and fish.

Plantae
Plants contain chlorophyll, a green pigment necessary for photosynthesis, a process in which plants
convert energy from sunlight into food. Their cell walls are made sturdy by a material called
cellulose, and they are fixed in one place. Plants are divided into two groups: flower- and fruit-
producing plants and those that don’t produce flowers or fruits. They include garden flowers,
agricultural crops, grasses, shrubs, ferns, mosses, and conifers.

Fungi
Fungi are usually motionless organisms that absorb nutrients for survival. They include
mushrooms, molds, and yeasts.

Protista
Protists are mostly single-celled organisms that have a nucleus. They usually live in water. Some protists
move around, while others stay in one place. Examples of protists include some algae, paramecium, and
amoeba.

Monera
Monera are single-celled organisms that don’t have a nucleus. Bacteria make up the entire kingdom. There
are more forms of bacteria than any other organism on Earth.


The Three Domain System

The three-domain system is a biological classification introduced by Carl Woese in 1977 that divides
cellular life forms into archaea, bacteria, and eukaryote domains. In particular, it emphasizes the separation
of prokaryotes into two groups, originally called Eubacteria (now Bacteria) and Archaebacteria (now Archaea).
Woese argued that, on the basis of differences in 16S rRNA genes, these two groups and the eukaryotes each
arose separately from an ancestor with poorly developed genetic machinery. To reflect these primary lines of
descent, the term "kingdom" was used to refer to the three primary phylogenic groupings now referred to as
"domains," until the latter term was coined in 1990.

Image

Archaea

The Archaea (singular archaeon) constitute a domain or kingdom of single-celled
microorganisms. These microbes have no cell nucleus or any other membrane-bound
organelles within their cells.

Bacteria

Bacteria (singular: bacterium) constitute a large domain or kingdom of prokaryotic
microorganisms. Typically a few micrometres in length, bacteria have a wide range of
shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to
appear on Earth, and are present in most habitats on the planet. Bacteria inhabit soil, water,
acidic hot springs, radioactive waste, and the deep portions of Earth's crust. Bacteria also live
in plants, animals (see symbiosis), and have flourished in manned space vehicles.
Eukaryote

A eukaryote is an organism whose cells contain a nucleus and other structures (organelles)
enclosed within membranes. Eukaryotes are formally the taxon Eukarya or Eukaryota. The
defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is
the nucleus, or nuclear envelope, within which the genetic material is carried. The presence
of a nucleus gives eukaryotes their name, which comes from the Greek ευ (eu, "good") and
κάρυον (karyon, "nut" or "kernel"). Most eukaryotic cells also contain other membrane-
bound organelles such as mitochondria or the Golgi apparatus. In addition, plants and algae
contain chloroplasts. Many unicellular organisms are eukaryotes, such as protozoa. All
multicellular organisms are eukaryotes, including animals, plants and fungi.

The Phylogenetic Tree could be expanded to look like the image below.

Image

Theosophy and Anthroposophy, and unified systems of science and metaphysics like those of
Arthur Young and Edward Haskell, all of whom added inanimate (e.g. mineral) and - in the
case of the theosophists non-physical ("elemental") kingdoms, giving all of them the same
grade as Animals and Plants.

Scientific evidence suggests that life began on Earth approximately 3.5 billion years ago. The
mechanism by which life emerged on Earth is unknown although many hypotheses have been
formulated. Since then, life has evolved into a wide variety of forms, which biologists have
classified into a hierarchy of taxa. Life can survive and thrive in a wide range of conditions.

Interesting facts: In a human body there are 10 times more microbes than human cells
There are approximately 210 distinct cell types in the adult human body.


The meaning of life—its significance, origin, purpose, and ultimate fate—is a central concept
and question in philosophy and religion. This is the theme I would like this topic to progress
toward...What is life; is it just the short span of seventy to eighty years that the average person
walks the earth, or is it more encompassing than that?


Ghislain
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