Students will be studying the structures of
prokaryotic cells and how these tiny organisms carry out all the
functions of living things. This is not a classification lesson, so
Archaebacteria and Eubacteria should not be discussed at this point.
Begin the lesson by telling students that on
May 20, 2010, scientists at the J. Craig Venter Institute in Maryland
created the first synthetic (man-made) organism. Dr. Craig Venter
hopes that Synthia,
M. mycoides JCVI-syn1.0 (nicknamed
can be programmed to make vaccines
or biofuels in the future. Ask students:
“How did Venter know Synthia
were life forms?” They exhibit
all the characteristics of living things. They are cells, which
obtain and use energy, reproduce, maintain homeostasis, grow and
develop, respond to stimuli and are adapted to their environment.
Venter did not claim they were alive
until they reproduced; however, the cells did exhibit these traits,
except perhaps adaptations because they were grown in a laboratory.
Tell students that
is a prokaryote, the same type of organism they will observe.
However, instead of observing the newest prokaryote, they will
observe two of the oldest prokaryotes used by man, Streptococcus
thermophilus and Lactobacillus bulgaricus, both
of which are found in yogurt. Show students the following microscopic
images (S-B-3-1_Prokaryote Pictures.doc).
Hand out copies of the What Do Prokaryotes
Look Like? worksheet (S-B-3-1_What Do Prokaryotes Look Like and KEY.doc).
Demonstrate how to make a wet mount
slide and stain the bacteria before allowing students to begin
Activity 1. Refer to the following Web sites for
instructions on preparing a wet mount slide:
Activity 1: Observing Bacteria on a
Wet Mount Slide
Have students work in small groups of
two or three. While students are working on the activity:
Ask students about their lab techniques and their
Make sure the slides are very clean. It is difficult
for students to tell the difference between dust and prokaryotic
Make sure their drawings include magnification and the size
is appropriately scaled to their field of vision.
After the activity, have students clean their slides and wash
Bacteria are tiny and students may not be
able to differentiate between the Streptococcus (spherical
shape) and the Lactobacillus (rod-shaped). If available, you
may want students to observe the cells with an oil emersion lens
(1000X), or have a microscope set up in the classroom so that
students can see the cells with the increased magnification.
Discuss the students’ observations. Lead
students to comment on the small size of the cells and how the cells
did not have a nucleus. Tell students that prokaryotes are the
simplest forms of life: “In fact, the name prokaryote
means before nucleus (pro = before; karyote = kernel or
nucleus). Prokaryotes are unicellular organisms that lack
a membrane bound nucleus. They lack many of the structures that are
found in the cells of plants and animals. Nevertheless, prokaryotes
are a very successful group of organisms. They have exploited more
habitats than any other group, including deep ocean vents, the gut of
cows, and your skin.” On the board, write down some places
bacteria live. Discuss “good” versus “bad” bacteria, and how
they can both help and harm people.
Note: If possible, before the lesson,
obtain a copy of Bill Bryson’s, “A Short History of Nearly
Everything” (see Related Resources).
Read the first two paragraphs of Bill
Bryson’s, “A Short History of Nearly Everything,” Chapter 20:
Small World, p. 302, or have students read the first two pages of the
essay. If you do not have a copy of the book, explain that bacteria
are prokaryotes and their success has to do with their structure.
Activity 2: Modeling Prokaryotes
Before this activity, make a model or find a
diagram of a typical prokaryotic cell to use for discussion after the
activity (S-B-3-1_Prokaryote Cell.docx).
Students will build and present a
three-dimensional model of a typical prokaryote cell, knowing only
names of the structures and their functions. Have students form
groups of two or three, give students the Parts of a Prokaryote
Worksheet (S-B-3-1_Parts of a Prokaryote Worksheet.doc) that describes the functions of each structure and
have supplies available. Students are not allowed to look in the book
or on the Internet to find pictures or diagrams of prokaryotes.
Write the materials and steps for building
their model on the board and have students write the steps on the
- Step 1
Discuss the structures and functions of the prokaryotic cell with
your group and hypothesize where the structures are located. List
the structures that belong at that location.
Within the membrane
Outside the membrane
Make a sketch of your model. Label each part and what material you
will use to represent it. Remind students that living things show
order; structures are not haphazardly attached to the cell.
Build and label the parts of the cell model. CAUTION: Hot glue is
HOT and can burn the skin! If you choose to use hot glue, have
the group show you a sketch before you give them the hot glue gun.
Avoid using clay or water. Clay tends to end up on the bottom of
shoes and students rarely make water-tight cell models.
1. Which of these structures help bacteria to survive in harsh
conditions, such as heat, and in the presence of disinfectants and
2. What happens when bacteria become resistant to antibiotics?
3. How do human activities increase our resistance to antibiotics?
4. How can we keep this from happening as often?
5. If you stop taking an antibiotic before you are finished with the
prescribed regimen, can it affect others as well as you?
Have students look at other groups’ cells
in a gallery walk (S-B-3-1_Prokaryote Model Gallery Walk and KEY.doc). Post questions with each model. Have
students record their responses to the questions posted at every
model but their own. As you circulate amongst students during the
gallery walk, listen for misinterpretations of the functions (e.g.,
the sex pilus is not for reproduction). Have students summarize their
findings in their science journals or notebooks.
Show students the teacher model or the
diagram of a prokaryote and discuss differences that they observe.
Discuss any misconceptions students revealed during the activity. For
instance, the sex pilus is for the exchange of genetic material; it
does not mean that the cell with the sex pilus is “male.” Also,
some students may have put the cell wall inside the cell membrane
because it is used for support (the human skeleton is used for
support inside the body). Explain that the cell wall controls how
much water enters the cell and it could not do that from inside the
membrane. Finally, since prokaryotes are unicellular, all
characteristics common to organisms are also the cell properties.
Each part of the prokaryote cell helps to carry on the processes of
living things. Ask how each prokaryotic structure relates to a
biological characteristic. Have students complete the Prokaryotic
Cell Structures and Functions Chart (S-B-3-1_Prokaryotic Cell Structures and Functions Chart and KEY.doc).
Students who may be going beyond the standards can
investigate the optimum growing conditions (i.e., temperature,
light) for bacteria collected from the soil, or lima bean water.
Students will need several agar plates, one to grow their first
culture and several for the test. Students should use proper
antiseptic techniques while conducting this research. Have students
share their findings with the class.
Students who may be going beyond the standards can answer the
Extension Questions for the Modeling Prokaryotes activity on Day 2.
Students who may require more practice with the standards can
label a diagram of the prokaryote cell with vocabulary tabs to help
learn the names and functions of structures (S-B-3-1_Prokaryotic Review.doc).