Microbiology LAB Exam #1 – Questions & Answers

Convert Celsius to Fahrenheit - ANSWER - F = (9xC)/5 +32 = How many decimel places, to the right of base - ANSWER - Six places --- .000 000 nm= How many decimel places, to the right of base - ANSWER - Nine places --- . 6.02x 10 = moving the decimel over how many spaces? - ANSWER - 23 Compare and contrast these three techniques by where bacteria grow in the media - ANSWER - Streak Plate - bacteria grow only on the surface Pour Plate - bacteria grow throughout the media Spread Plate - bacteria grow only on the surface Differentiate between a pure culture, mixed culture, and contaminated culture. - ANSWER - Pure - only one type of bacteria is present in a culture. Mixed - two or more types of bacteria are contained within a culture (intentionally.) Contaminated - two or more types of bacteria are found in a culture (unintentionally.) Explain the purpose of inverting plates when incubating. - ANSWER - Inverting plates makes sure that condensed water does not fall on the surface of agar plates. Water that falls on the plate will mix different colonies together and not allow isolated colonies to appear on the surface What is the purpose of the Standard Plate Count? - ANSWER - To determine how many Colony Forming Units/ml are present. What is the range CFUs/plate that are countable? - ANSWER - 30-300 CFUs per plate are statistically significant. What are two assumptions that are made in the SPC? - ANSWER - 1) That all bacteria will grow in the media and under conditions provided. 2) That one bacteria results in one colony forming unit. Describe how to make a specific dilution (like 1:10 or 1:100). - ANSWER - To make a 1:10 dilution, 1 ml of the sample is added to 9 ml of sterile water. This gives a 1:10 dilution because the dilution is calculated by amount added divided by the final volume. (1/1+9 = 1/10) Describe how to calculate the dilution, total dilution, and number of CFU's/ml of the original sample. - ANSWER - Calculate dilution by taking the amount added divided by