LECTURE                                         CLASSIFICATIONS OF LIVING THINGS

In this lecture you will learn about:

We are now at the midpoint of the semester.  We looked at how atoms combine into organic matter, and how cells are built out of the organic molecules. 

The vast majority of living things on Earth are not organized into anything more complex than a single cell.  And everything more complex starts as a single cell anyway called an egg. Humans like order and like to classify things, like the periodic table for elements.  We will look at how living cells are classified. 

So the next step in classification is into procaryotes and eucaryotes except there is an older group of microbes, the Archae that were added. So instead of two basic "domains" there are three domains of life. 

While two of the three domains are all single celled, the third, eucaryotes have both single celled and multiple celled members. 

Multicellularity occurs under the direction of the "program" encoded in DNA so that a single cell/egg divides into many cells and rather than the cells parting ways and drifting off like bacteria the cells stay glued together and work cooperatively in ways more complex than a single cell.  Only eucaryotes can do this. 

In addition as complexity increases the groups of cells begin to specialize into "tissues" that perform specific functions. At a higher level of complexity the tissues group into organ systems within the body of the organism. Interestingly, organism is a rather generic term used to designate a single living thing and does not promise they have "organs". 

It is the division of eucaryotes into single and multiple cells that leads to a system of "kingdoms" where single cells get one kingdom (Protista) and multiple celled critters are divided into 3 additional kingdoms mostly based on how they make a living. 



"Living things are divided into three groups based on their genetic similarity. The three groups are:

    * Archaea: very ancient prokaryotic microbes.

    * Bacteria: More advanced prokaryotic microbes.

    * Eukaryota: All life forms with eukaryotic cells including plants and animals

These three groups are called domains. The figure at the left shows the three domains of life. The distance between groups indicates how closely related they are. Groups that are close together, like plants and animals, are much more closely related than groups that are far apart, like plants and bacteria. Do you see how the two types of microbes, Archaea and Bacteria, are about as similar to one another as they are to animals? Recent studies have found that microbes are far more diverse than anyone had suspected. "


This is the kingdom of the bacteria.

This is the kingdom of the eucaryotes that are single celled like algae some of the diseases of humans like malaria.

This is the kingdom of the eukaryotes that are like plants but DONT photosynthesize, rather they secrete chemicals that break down other living things and absorb their nutrition.  Yeasts and mushrooms are in this kingdom. 

This is the kingdom of the eucaryotes that photosynthesize and create sugar out of light, water and CO2. 

This is the kingdom of the eucaryotes that DONT photosynthesize but must eat what other living things produce. 

Notice that viruses dont make the list.  They are not considered "living" in the same sense as celled organisms. 

"TAXONOMY --the branch of science that classifies and names living things.

NOMENCLATURE --a system for naming things

In biology there is a two-word system that is used to name organisms. It is called BINOMIAL NOMENCLATURE (a two named--naming system).

Carolus Linnaeus devised this in the 1800's using these two subgroups for the name:

(more general) (more specific)"

Go and find the entire classification for domesticated dogs.

Taxonomy based on: 

Anatomical homology 

this is the "old" way of classifying things, "if they look alike, they are alike". But it falls down when there are birds that have color variation, for example. 


Taxonomy based on: 

Protein Sequences
          o Hemoglobins
          o Cytochrome c
          o Phylogenetic trees

DNA Sequences - the new way of classifying things

With such information, one can reconstruct an evolutionary history of the molecule and thus of their respective owners. This requires

    * using the genetic code to determine the minimum number of nucleotide substitutions in the DNA of the gene needed to derive one protein from another and

    * a powerful computer program to search for the shortest paths linking the molecules together.

Appearance Not Always Enough to Identify Species

- before 1980's and after