Biotic or Abiotic: What Does It Mean To Be Living?
Everything in our physical world is built out of matter. Some things in our world are living and some things are nonliving but all of them are made from matter, which itself is not living. Two important scientific words that mean living are biotic and organic. Biotic comes from the Greek biōtikós which means “pertaining to life” or bios, simply meaning life, hence biography is story of someone’s life, biology is the study of life. Organic comes from Latin organicus, "serving as an organ or instrument," and Greek órganon, implement, tool, bodily organ, akin to érgon work.
Non-living things can be called abiotic (a- “not” biotic/living) and inorganic (in- “not, opposite of” organic). Abiotic matter is abundant in the universe. All of the objects that we know of outside of earth, suns/stars, moons, planets, asteroids, and everything else are abiotic (no living things have yet been identified). This is a massive, incomprehensible amount of matter! The vast majority of matter on earth is abiotic: oceans of water, mountains of rock and dirt, and heaps of man-made goods (cell phones, airplanes, bottles, concrete).
Non-living things should not be confused with dead things. In fact a defining characteristic of a living thing is that it can die, however, even dead, it is still organic. This is because all organic matter contain particular chemical compounds which are carbon-based. Inorganic matter is not carbon-based. So even dead things that were once alive are considered organic. Abiotic things never were and never will be alive.
Living, biotic, things are rare in the universe, but common on Earth. Any living thing can be referred to as an organism (Greek ὄργανον “organ” and the –ism “process”', “state”). All organisms are made of atoms in different combinations of molecules. The atoms and molecules from which they are built are not what we consider living. Living things have special properties and characteristics that non-living things lack.
Life
So, what does it mean to be living? Physicist Erwin Schrodinger said, “The arrangement of the atoms in the most vital part of an organism differ in a fundamental way from all those arrangements of atoms which physicists and chemists have hitherto made the object of their experimental and theoretical research. The situation is unprecedented—it is unknown anywhere else except in living matter.”1
First and most obviously, living things can die. Even creatures like lobsters and the Immortal Jellyfish (Turritopsis doohmii) which live for extremely long times, can be killed or die from disease. Main characteristics of life include the ability to reproduce, movement (which may happen internally or at the cell level), responding to the environment, i.e., avoid harm/death, maintaining homeostasis (keep their internal environment in balance, hydrated, right temperature, etc.) and passing traits on to offspring.
All organisms are built from a basic structural unit called a cells. There are single-celled organisms (amoebas, protozoa), simple multi-celled organisms (bacteria, algae), and complex organisms that are built from numerous systems of cell groups working together (trees, humans).
Kingdoms of Life
Figure 1: The Kingdoms of Living Organisms
Because smaller units and groupings of similar things are easier to study and understand, part of scientists’ job is to classify and organize information. All living things have been categorized according to similarities in grouping called a taxonomy (from Greek taxis "arrangement" + -nomia "method") Aristotle (300c B.C.) divided the world into two kingdoms, plant and animal. Later, German biologist Earnst Haeckel (1866) added Protists, single celled organisms. In 1969, R. H. Whittaker added Fungi. Carolus Linnaeus is widely recognized for his Systema Naturae (1735) which established the animal, vegetable and mineral kingdoms. Scientists currently recognize six kingdoms. Listed from most complex to least complex, these kingdoms are Animals, Plants, Fungi, Protists (mostly single celled organisms), Eubacteria (all are single-celled), and Archaebacteia.
Animals are multicellular organisms that consume organic matter for energy. They can move independently for at least part of their life cycle and have thin cell membranes. The Kingdom Animalia includes mammals, birds, insects, reptiles and arthropods.
Plants have rigid cell walls stiffened by cellulose and do not move independently. Chlorophyll in their cells creates energy from sunlight and carbon dioxide. Plants include trees, bushes, grasses, ferns and green algae.
Fungi, like plants, have stiff cell walls and do not move independently. Like ferns, they reproduce through spores but they differ from plants because, like animals, fungi consume external organic matter for energy, and have no chlorophyll and no cellulose. Mushrooms, yeasts and molds are members of the Kingdom Fungi.
Protists have only one cell or are cell colonies that do not form differentiated tissues. These cells contain a nucleus and organelles. Protozoa, red algae, slime molds and water molds are all Protists.
Eubacteria, also called Bacteria and Monera, are single-celled organisms that lack organized nuclei and rarely have organelles. Bacterial organisms are found everywhere on Earth from deep-sea hot springs to the human gut.
Archaebacteria, or Archaea, are single-celled organisms without a distinct nucleus or organelles. They resemble bacteria but have different genetic structures and metabolic processes. Archaebacteria were once thought to live only in extreme environments like sulfur springs but have been found all over the Earth. They are especially plentiful in plankton.
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