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THE ORGANIZATION OF LIFE

The living world can be considered a hierarchy, with each level of biological structure and organization building upon the level below it. From "simplest" to most complex, biological things are composed of...
  • molecules combine to form larger molecules which combine to form...
  • cell organelles, which are the subunits of...
  • cells

    The CELL is the smallest unit of life. Cells may join to form...

  • tissues, which may be... ...and combine to form
  • organs, which combine to form...
  • organ systems, which combine to form...
  • organisms!

    Let's digress just a bit and discuss molecules...

    Cast your eyes skywards, to the periodic table of elements...
    (You can also access a copy right from your own computer at http://periodic.lanl.gov/default.htm.)

    All living things are composed of MOLECULES.
    A molecule is two or more ATOMS (composed of protons (+) and neutrons (0) to make the nucleus, and orbited by electrons (-) bonded together. They may be the same type of atom (which means that the molecule is an ELEMENT), or they may be different types of atoms (which means that the molecule is a COMPOUND).

    Examples of elements: O2, H2, N2, etc.
    Examples of compounds: H2O, CO2, CH4, etc.

    An ORGANIC molecule is one which has a basic "skeleton" made of CARBON (C) and HYDROGEN. They are so named because these types of molecules usually are made only by LIVING ORGANISMS. (That's changed with the advent of modern chemistry--but originally, organic molecules were made almost exclusively by living organisms.)

    Examples of organic molecules: CH4 (methane), benzene (C6H6), the sugar glucose (C6H12O6), etc.

    An INORGANIC molecule is one that lacks that CARBON-HYDROGEN backbone. Examples are among the elements and compounds I listed above:
    O2, H2, N2, H2O, and CO2

    Molecules combine to form the next level of complexity in biological systems, the BIOLOGICAL MACROMOLECULES.

    The structural components of the bodies of all living things are mostly very large, compound molecules known as BIOLOGICAL MACROMOLECULES (though there are lots of other inorganic and smaller organic molecules throughout the body, too). The four main types of biological macromolecules are...

    Biological macromolecules listed above are POLYMERS: long chains of repeating subunits. In the case of each:

    What are the main functions of each type of macromolecule?
    All form components of cellular structures and organelles.
    In multicellular organisms...