1. Look at your results and discuss the differences in the number of colonies between plates from the same sample (time) but different dilutions. What difference did you expect to find?
2. Give an example of how you calculated the concentration of viable cells from the number of colonies counted for your chosen dilution.
3. Record whether your plates contained one or more TYPES of microorganisms. What does it mean if more than one type of microorganisms are present?
4. Using your data, produce a graph of your log (cfu/ml) vs time at your test temperature. Calculate the corresponding D value
5. Using class data, produce a graph of your log (cfu/ml) vs time at ALL tested temperatures and calculate the D values.
6. Compare the D values obtained from 4. And 5. And discuss the results
7. Using the D values calculated in 5. Plot Log (D value) vs Temperature and calculate (or estimate) the Z value. As points below - You may need to refer to literature available online to find whether your lab data allowed you to calculate or estimate a likely Z value.
8. Discuss your results, their meaning and how they compare with the D and Z value known for Bacillus from literature.
9. What does the literature give for a D and Z score for a particular Bacillus species (name the species)?