Download Observing Bacteria Types

HHMI Prokaryotes-T
PROKARYOTIC CELLS
TEACHER NOTES
Alabama Course of Study-Science
Biology: 1-Select appropriate laboratory glassware, balances, time measuring equipment, and
optical instruments to conduct an experiment.
Biology: 4-Describe similarities and differences of cell organelles, using diagrams and tables.
Distinguishing between prokaryotic and eukaryotic cells.
Biology: 9-Differentiate between the kingdoms. Identifying ways in which organisms from the
kingdoms are beneficial and harmful.
TIME
Prep Time: 15 minutes set up microscopes and distribute prepared bacteria slides.
Lab Time: 40 minutes to view, sketch, answer questions, and clean up.
GROUP SIZE
One or two students per microscope.
SAFETY
Follow standard laboratory procedures as required when working with microscopes and glass
slides.
Be sure students are careful if using methylene blue stain not to get it on their skin or clothing.
Reassure any concerned students that the bacteria on the prepared slide are dead and preserved
and therefore cannot infect them.
Preparation
Provide lens paper to remove smudges from prepared slides. Make sure adequate number of
slides and microscopes are available depending on class size. Secure extension cords if needed.
Use plain yogurt.
ENGAGE
Option 1: Have students compare and contrast prokaryotic and eukaryotic cells.
1. Prokaryotic Cell-Before nucleus
2. Eukaryotic Cell-New nucleus
3. The smaller cell
4.
Eukaryotic Cells
More than one chromosome
Reproduction involves meiosis
True nucleus
10-100 micrometers
Divides by mitosis
Cytoplasmic streaming
Membrane-bound organelles
Cytoskeleton always present
May 2012
Both
DNA
Plasma membrane
Prokaryotic Cells
.2-2 micrometers
One chromosome
Divides by binary fission
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HHMI Prokaryotes-T
After going over the answers, ask students, “how are prokaryotic cells different?”
Option 2: Have students view a video such as “Simple Organisms: Bacteria”, “Ebola- The Way
of All Flesh”, etc…
Option 3: Ask students several questions about bacteria to gain an understanding of their
knowledge:
1. What are bacteria?
Prokaryotic life form.
2. Where are bacteria located?
Bacteria are found throughout the earth in aerobic and anaerobic conditions.
3. Are all bacteria harmful?
No, some are decomposers and help break down complex molecules into smaller
units for absorption by the intestines or roots of plants (Nitrogen-fixing bacteria).
Scientists have discovered that the presence of certain kinds of bacteria is
essential for the human body. There are many bacteria that live in the human
intestines that contribute to proper digestion. These good bacteria don’t let in bad
bacteria and help us digest food that we are unable to process on our own. These
bacteria also help to get rid of toxins in our body. Good bacteria improve milk
tolerance, regulate digestive function, improve immune response, aid in
absorption of nutrients, and decrease food allergies. Many of these helpful
bacteria are found in foods such as yogurt, buttermilk, cheese, and vinegar.
4. Can you see a bacterium with the naked eye?
No, bacteria are microscopic. However colonies of bacteria (which consist of millions
of individual cells) are visible with the naked eye.
EXPLORE
Part I.
Obtain a prepared slide containing the three various shapes on a bacteria smear. Follow proper
microscope procedures to sketch each shape on the student worksheet. Label and color each
sketch. Answer questions after completing sketches.
PartII.
Obtain clean slides and cover slips to prepare a thin smear of plain yogurt for microscopic
viewing. Add a drop of Methylene blue and water prior to placing the clover slip over the
specimen. Follow proper microscope procedures to sketch each shape on the student worksheet.
Label and color each sketch. Answer questions after completing sketches.
Troubleshooting
Check all electrical cords for proper attachment to electrical plugs.
Do not use electrical cords that are frayed or damaged.
Make sure prepared slides are clean.
Make sure the scanning (4X) objective is used to locate the specimen prior to using the low (10x)
and high (40x) power objectives.
Yogurt at room temperature may give better results.
Make sure students do not use too much yogurt on their slide.
Make sure students don’t confuse the yogurt clumps for bacteria.
May 2012
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HHMI Prokaryotes-T
Sample Data:
Answers to Analysis Questions
Part I
1. List three characteristics of prokaryotic cells that distinguish them from eukaryotic cells.
No nucleus, Circular ring of DNA, lack membrane bound organelles, smaller than eukaryotic
cells, have different cell shapes
2.
A.
B.
C.
Name and describe the three common shapes of bacteria.
Coccus –round or spherical
Bacillus-rod
Spirillum-spiral
3. A doctor informs you that you have a Streptococcus pyogenes (Strep Throat) infection.
A. Use your knowledge to impress her by drawing a picture what this bacteria would look
like below.
B. Would the doctor treat this infection with antibiotics? Explain.
Yes, this is a bacterial infection and antibiotics can kill bacteria.
4. Why is it necessary to stain bacteria prior to microscopic viewing?
The bacteria are transparent and difficult to view prior to staining
Part II
1. How many different kinds of bacteria could you find in the yogurt?
Answers will vary. Most are cocci and bacilli. Make sure students also note if they were Diplo-,
Strepto-, etc.
2. Can you see a nucleus in the bacteria?
No nucleus exists and the nucloid is too small to be viewed with the compound microscope.
3. Why is it necessary to stain bacteria prior to microscopic viewing?
May 2012
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HHMI Prokaryotes-T
The stain adheres to the bacteria, making them easier to see.
EXPLAIN
When most people think of bacteria, they think of disease-causing organisms, like the
Streptococcus bacteria, which cause strep throat. While bacteria are notorious for such diseases
as tetanus, tuberculosis, and salmonella poisoning, such disease-causing species are a
comparatively tiny fraction of the bacteria as a whole.
Bacteria are so widespread that it is possible only to make the most general statements about
their behaviors and appearances. Bacteria are prokaryotes. They contain a circular ring of DNA.
Bacteria lack membrane-bound organelles. Most bacteria are colorless. This feature makes
them difficult to view under a microscope.
They may be found on the tops of the highest mountains, the bottoms of the deepest oceans, in
the guts of animals, and even on the frozen rocks and ice of Antarctica. One feature that has
enabled them to spread so far, and last so long is their ability to go dormant for extended periods
of time. When conditions are good they come out of dormancy to grow and reproduce.
Most bacteria are considered decomposers and help break down complex molecules into smaller
units. This same process occurs in the intestines of animals and the roots of some plants (e.g.
nitrogen fixing bacteria). There are many bacteria that live in the human intestines that
contribute to proper digestion. Scientists have discovered that the presence of certain bacteria is
essential for the human body. These good bacteria out compete bad bacteria under normal
conditions and help us digest food that we are unable to process on our own. These bacteria also
help to get rid of toxins in our body. Good bacteria improve milk tolerance, regulate digestive
function, improve immune response, aid in absorption of nutrients, and decrease food allergies.
Many of these helpful bacteria are found in foods such as yogurt, buttermilk, cheese, and
vinegar.
EVALUATE
Students should be graded on microscope use, sketches, and answers to questions.
EXTEND
1. Complete the “Antibiotic Resistance” activity.
2. Discuss Gram staining. Review slides to determine which bacteria are Gram positive and
which are Gram negative.
3. Make yogurt.
May 2012
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