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B2 1.3a – Student practical sheet
Bacterial and yeast cells
Microscopic bacteria and yeast cells have characteristic cell structures.
Aim
Examine bacterial cells from a yogurt culture, and yeast cells from a yeast suspension, under the
microscope. With the help of photomicrographs and electron micrographs of bacterial and yeast
cells, explore bacterial and yeast cell structure.
Equipment
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absorbent tissue
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glass rod
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mounted needle
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2 coverslips
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lens tissue
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2 slides
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distilled water wash bottle
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live yogurt culture
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yeast suspension
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2 dropping pipettes
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microscope
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eye protection
Safety
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Eye protection required.
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Avoid skin contact with yeast suspension.
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Wash your hands after this activity.
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Dispose of slides and coverslips as instructed by your teacher.
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Tell your teacher if you break glass slides.
What you need to do
1
Place a tiny dab of yogurt on a microscope slide using a glass rod.
2
Add a small drop of water to the yogurt and mix it with a mounted needle, without spreading it
over the slide.
3
Add a coverslip, lowering it onto the yogurt/water drop with the help of a mounted needle..
4
Focus the high-power ×40 objective lens to see cells of Lactobacillus bacteria and draw three
or four cells.
5
On a clean slide place a small spot of yeast suspension using a dropping pipette. Add a
coverslip, examine and draw three yeast cells under the ×40 objective lens.
6
Using the photo/electron micrographs provided, draw a sketch of a bacterial cell and a yeast
cell and label your drawings.
7
Note the magnification of each photo/electron micrograph and adjust the magnification to
estimate the magnification of your own drawings.
Using the evidence
1
Describe the shape of the yogurt bacteria and yeast cells. (2 marks)
2
Make a table to compare the structure of bacterial and yeast cells. Your table should include
reference to cell wall, nucleus (if any), cytoplasm, cell membrane, vacuoles, cell shape, cell
size. (6 marks)
Sheet 1 of 2
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153
B2 1.3a – Student practical sheet
Evaluation
3
Suggest how you could have made the Lactobacillus cells easier to see. (2 marks)
4
How did you adjust the magnification of the electron micrographs to correspond with your own
drawing? How could you improve your estimate of magnification? (2 marks)
Extension
5
Find out how yeast cells reproduce by budding and make a labelled sketch to show this.
(2 marks)
6
Research to find three common shapes of bacteria and the meaning of Gram positive and
Gram negative bacteria. (3 marks)
Sheet 2 of 2
154
© Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free.