C-6
Name: ______________________________
SCIENCE – The Cell
February 2008
Section #/color: ___ / _________
TRIO TEAM CHALLENGE
Since your team has the advantage of having THREE people to pull the same weight as the other
teams of only two, you have the assignment to take on the TRIO TEAM CHALLENGE.
You see, there are really THREE general groups of cells:
PLANT, ANIMAL,
and
BACTERIAL.
One person in your group – one that is willing to take on the challenge of learning something extra –
will be making the bacterial cell model in addition to the plant and animal cell models that all the other
duo teams are doing!
Here is information to start your extra-challenge on an easier course:
Bacterial Cell Structure
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Nucleoid
DNA
Ribosomes
Cell wall
Plasma membrane
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Outer membrane
Capsule
Flagella
Pili
Internal Structure: Bacteria have a very simple internal structure, and no
membrane-bound organelles.
nucleoid
DNA in the bacterial cell is generally confined to
this central region. Though it isn't bounded by a
membrane, it is visibly distinct (by transmission
microscopy) from the rest of the cell interior.
ribosomes
Ribosomes give the cytoplasm of bacteria a
granular appearance in electron micrographs.
Though smaller than the ribosomes in eukaryotic
cells, these inclusions have a similar function in
translating the genetic message in messenger
RNA into the production of peptide sequences
(proteins).
storage
granules
(not shown) Nutrients and reserves may be stored
in the cytoplasm in the form of glycogen, lipids,
polyphosphate, or in some cases, sulfur or
nitrogen.
(not shown) Some bacteria, like Clostridium
botulinum, form spores that are highly resistant
to drought, high temperature and other
endospore environmental hazards. Once the hazard is
removed, the spore germinates to create a new
population.
Surface Structure: Beginning from the outermost structure and moving inward,
bacteria have some or all of the following structures:
capsule
This layer of polysaccharide (sometimes
proteins) protects the bacterial cell and is often
associated with pathogenic bacteria because it
serves as a barrier against phagocytosis by
white blood cells.
outer
membrane
(not shown) This lipid bilayer is found in Gram
negative bacteria and is the source of
lipopolysaccharide (LPS) in these bacteria. LPS
is toxic and turns on the immune system of , but
not in Gram positive bacteria.
cell wall
Composed of peptidoglycan (polysaccharides +
protein), the cell wall maintains the overall shape
of a bacterial cell. The three primary shapes in
bacteria are coccus (spherical), bacillus (rodshaped) and spirillum (spiral). Mycoplasma are
bacteria that have no cell wall and therefore have
no definite shape.
(not shown) This cellular compartment is found
only in those bacteria that have both an outer
periplasmic membrane and plasma membrane (e.g. Gram
negative bacteria). In the space are enzymes and
space
other proteins that help digest and move
nutrients into the cell.
plasma
membrane
This is a lipid bilayer much like the cytoplasmic
(plasma) membrane of other cells. There are
numerous proteins moving within or upon this
layer that are primarily responsible for transport
of ions, nutrients and waste across the
membrane.
Appendages: Bacteria may have the following appendages:
pili
These are hollow, hairlike structures made of protein
allow bacteria to attach to other cells. A specialized
pilus, the sex pilus, allows the transfer from one
bacterial cell to another. Pili (sing., pilus) are also
called fimbriae (sing., fimbria).
The purpose of flagella (sing., flagellum) is motility.
Flagella are long appendages which rotate by means
flagella of a "motor" located just under the cytoplasmic
membrane. Bacteria may have one, a few, or many
flagella in different positions on the cell.