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Exercise 5. Microscopic Study of Living Yeast and Molds 
MATERIALS: 
Culture of yeast on dextrose agar 
Cultures of molds on potato agar 
1. Place three or four drops of the yeast suspension upon a plain slide. 
Cover with a clean cover glass. The cover glass should float on the liquid 
which should be sufficient in amount to extend under the cover glass, but 
should not cover the upper surface so that it comes in contact with the 
objective. 
2. Examine the preparation with a 4 m. m. objective. Draw and describe 
the organisms. 
3. Examine the pure cultures of molds in the Petri dishes. Describe their 
naked eye appearance. 
4. Place the dish on the stage of the microscope with the cover removed. 
Examine the patches, preferably the edge, with the 16 m. m. objective. 
Notice the color, form, and size of the patch of mold. Notice the filaments 
which grow on the jelly-like food substance and the erect ones carrying the 
spores. 
5. Make a more detailed examination of the filaments and spores using the 
4 m. m. objective. 
6. Make a large detailed drawing of each of the molds furnished. In each 
case show the following: 
(a) Mycelium and filament structure. 
(b) Fertile hyphae. 
(c) Sporangia and spores. 
(tf) Label all of the parts and give the/genus of each mold studied. 
7. (a) How do molds differ from bacteria. 
(b) How do they differ from yeasts? 
(c) How do the molds reproduce? 
( d ) How yeasts reproduce? 
( e ) How do yeasts compare in size with bacteria? 
