Download Classification Reading

The Classification of Living Things:
Directions – Take notes for your starter. Most of this should be a review and you already have notes over much of
this in your comp. books.
Now that we have defined life, we seek to sort and categorize those organisms. Carolus Linnaeus came up with a system that
although modified by new discoveries, we still use today. As the understanding of organisms improved, it became necessary
to adjust the system of biological classification. Two things in particular have had a large effect on biological classification.
One of these is Charles Darwin's theory of evolution. The other is advances in technology that have enabled scientists to
take a better look at organisms.
Evolution and Classification
Today, more than 200 years after Linnaeus completed his work, scientists consider many factors when classifying organisms.
Of course, they still examine the large internal and external structures as Linnaeus did, but now with the advances in
technology, they also rely on other observations.
Today scientists use a database that contains all the known genetic
sequences of organisms to help determine evolutionary relationships between organisms.
DNA and RNA comparisons
between organisms are relied upon for more accurate classifications of organisms. By comparing similar genes, or sequences
of DNA, we can tell how similar the two species genetic codes are.
Similar sequences between species indicate close
evolutionary relationships. Scientists conclude from various studies that human DNA is about 96% similar to a chimpanzee’s
DNA. This number has changed as scientists learn more about genetics. In fact, chimps have two more chromosomes than
humans, but we still share many similar genes. Many genes show a 99% similarity between us.
Linnaeus’s system, modernized by scientists as technology improved, groups organisms according to basic characteristics
that reflect their evolutionary relationships. All living things are classified into eight major groups: Domain, Kingdom,
Phylum, Class, Order, Family, Genus and species. The largest and most general group is the Domain. For example, all
protists, plants, fungi, and animals belong to the Domain Eukaryota. The second largest group is the Kingdom. A Domain
includes a large number of very different organisms. However, these organisms share some important characteristics. A
species is the smallest and most specific group in the classification system. Members of the same species share many
characteristics and are similar to one another in appearance and behavior. In addition, members of the same species can
interbreed and produce viable offspring. Viable means that the offspring are in turn able to produce offspring of their own.
Linnaeus’s system also gives each organism a unique scientific name that scientists all over the world can use and understand.
The scientific name consists of both the Genus and species name.
The Domains and the Kingdoms of all Living Things
Domain Archaea > Kingdom Archaebacteria
The Archaea Domain is the first domain. The organisms within Archaea are composed of some of the oldest species on
Earth. All organisms in this domain fall within the Kingdom Archeabacteria and are often referred to as such. This term
however is misleading, as their genetic make-up is actually more similar to animals than bacteria. They are not bacteria, they
are uniquely Archaea. Most archaens are known as extremophiles, because they live in extreme environments, such as the
halophiles which thrive in salt, or thermophiles which live in temperatures of up to 110 degrees Celcius. Archaens are
unicellular (composed of one cell) and they have a cell membrane and a cell wall that separates their internal environment
from their external environment. They are prokaryotes, thus, they have no membrane bound organelles inside their cell
membrane.
Organelles are structures that organize the cell’s internal components, surround and protect the genetic
material (nucleus), and generally increase the productivity and efficiency of the cell. Archaens gather energy in a variety of
ways, but they are all autotrophic.
chemicals (chemoautotrophs).
They obtain energy by making their own food using sunlight (photoautotrophs) or
Domain Bacteria > Kingdom Eubacteria
The Domain, Bacteria, consists of the second set of organisms to evolve on earth. There are about 40 million bacteria in a
small pinch of dirt and the collective biomass of all the bacteria on Earth is more than that of all plants and animals
combined! All organisms within this domain are found within the Kingdom Eubacteria. Many structures and biochemical
properties of bacteria are unique to this group and are not found in Archaea or Eukaryota. Bacteria are all unicellular
prokaryotes. Bacteria have a cell membrane, and a cell wall around the membrane as further protection from the
environment.
This cell wall also defines the shape of bacteria.
Bacteria are either coccus (spherical), bacillus (rods),
spirillum (spirals) or filamentous. Bacteria are either heterotrophs or photoautotrophs.
Cynobacteria perform
photosynthesis and are considered the first oxygen producing photoautotrophs to evolve on Earth. Heterotrophic bacteria
gather food from their environment.
Domain Eukaryota > Kingdom Protista, Kingdom Fungi, Kingdom Plantae, Kingdom Animalia
The third and final domain is Eukaryota. All members of Eukaryota are eukaryotes. Eukaryotes have a highly organized
cellular structure that includes organelles. Organelles carryout specific tasks and improve the efficiency of the cell. One
noticeable structure found in eukaryotic cells is the nucleus which houses and protects the genetic material in a cell. Domain
Eukaryota contains the Kingdoms Protista, Fungi, Plantae, and Amimalia.
Kingdom Protista.
Protists are the only unicellular eukaryotes, although some species live together in large colonies that
give the appearance of being multicellular.
Plant-like protists are photoautotrophs, have a cell wall and most are capable of
movement. They produce 70% of the world’s oxygen and support most of the world’s marine food chains. Animal-like protists
are heterotrophs with no cell wall and most can move. Fungi-like protists are saprotrophs with a cell wall and can also move.
Kingdom Fungi: These are multicellular organisms that lack photosynthetic pigments and absorb nutrients directly from
their surroundings by decomposing dead organisms (saprotrophs). The cells of a fungus have a cell wall surrounding each cell
membrane. Mushrooms and toadstools are fungi, as are the molds that sometimes grow on leftover foods that have remained
too long in the refrigerator. The mildews that may appear as small black spots in damp basements and bathrooms are also
fungi.
Kingdom Plantae:
Plants make up this kingdom.
These organisms are multicellular photoautotrophs.
Plant cells are
surrounded by a tough cell wall. Cell walls help the plant form and maintain a shape while providing extra protections for the
cell. You are probably quite familiar with members of this kingdom, which includes flowering plants, mosses, ferns and trees.
Kingdom Animalia: Animals are multicellular organisms with specialized tissues. All animals are heterotrophs with no cell
walls.
DIRECTIONS: Use these to help guide your note taking.
1. 2. What is evolution, and how does it affect the way organisms are classified?
2. What is the order in which the kingdoms evolved on earth.
3. Explain why knowing the classification of an unfamiliar organism can tell you a lot about that organism.
4. Make a chart showing the three domains and the six kingdoms of living organisms and list three important
characteristics of each of the five kingdoms.
5. How is the way an autotroph gets food different from the way a heterotroph gets food?
6. Suppose that creatures from a distant planet are multicellular heterotrophs whose cells lack cell walls. Which domain
and kingdom of the Earth's organisms do these creatures most closely resemble?