Name: Sara BolandLab: Saturday, 8:00 a.m.

Lab Name: Osmosis Lab

Purpose: Various microorganisms are responsible for the spoilage of food. Some methods of food preservation have been the use of salt or sugar to inhibit microbial growth. This was likely a secondary result of the use of both salt and sugar. They were probably both used to enhance the flavor of the food but a lovely side-benefit was that these seasonings actually helped to preserve the food. The science behind this is the principle of plasmolysis. The majority of microorganisms can tolerate slight osmotic changes, but when a microbe is surrounded by a strongly hypertonic solution (very salty), the microorganism is usually inhibited or killed because the cell has shed too much water and the plasma membrane separates from the cell wall (plasmolysis). Sugar will also inhibit microbial growth through plasmolysis although it needs to be present in much higher concentrations than salt. The microbes being used in this lab run the gamut from bacteria to yeast. In this lab we are looking to observe the inhibitory effects of both salt and sugar and the differences in effectiveness between the two by observing samples of five different microorganisms in media laced with one or the other.

Materials:-hot plate -water bath-petri dishes -sterile applicator swabs-bottle nutrient agar -bottle nutrient agar with 0.5% sucrose-bottle nutrient agar with 30% sucrose -bottle nutrient agar with 60% sucrose-bottle nutrient agar with 0.5% salt -bottle nutrient agar with 15% salt-bottle nutrient agar with 30% salt -wax pencil

Organisms:-Bacillus cereus -Penicillium chrysogenum-Pseudomonas fluorescens -Saccharomyces cerevisiae-Serratia marcescens

Procedure:

1. Disinfect work surface2. Loosen the caps of the agar and place in the boiling water bath making sure the water level is well above the line of agar in the bottle. Leave the bottles in the boiling water bath until the agar is melted.3. Remove the cap from the agar bottle and pour the agar into five petri dishes. Cover the petri dishes immediately following pouring to prevent any contamination.4. Repeat step two with the other bottles of agar being used.

5. Using an applicator stick which has been carefully removed from packaging to avoid any contamination, pick up some material from the culture dish and spread culture in an even line down the center of the petri dish containing agar. 6. Repeat step five for the other petri dishes containing agar.7. Clearly label the petri dishes with: type of agar, culture name, group name and date.8. Leave cultured petri dishes at room temperature for five days.9. After seven days examine the cultured petri dishes for growth using the plain nutrient agar as a control. . Label this petri dish +++. Compare the other samples to this dish and record the growth of the cultures in the other dishes as: marked growth (+++), moderate growth (++), slight growth (+) and no growth (-).

Results:

Organism Nutrient Agar 0.5% Sucrose Agar

30% Sucrose Agar

60 % Sucrose Agar

B. cereusP. chrysogenumP. fluorescens

S. cerevisiaeS. marcescens

Organism 0.5% Salt Agar 15% Salt Agar 30% Salt AgarB. cereusP. chrysogenumP. fluorescensS. cerevisiaeS. marcescens