Q: You are preparing 20 agar deeps, each requiring 15 ml of Trypticase Soy Agar (TSA). How many grams of dehydrated TSA powder are needed to make the required volume? (TSA: $$40$$ grams per $$1000 ml)$$

$$12.0$$ grams$$\ (20 \times 15 = 300\ ml;\ \frac{40}{1000} \times 300 = 12\ grams)$$

Q: A student needs to prepare 10 slants, each with 10 ml of Trypticase Soy Agar (TSA). How much TSA powder should be weighed out? (TSA: $$40$$ grams per $$1000 ml)$$

$$4.0$$ grams$$\ (10 \times 10 = 100\ ml;\ \frac{40}{1000} \times 100 = 4\ grams)$$

Q: A student is preparing 12 broths, each requiring 5 ml of Trypticase Soy Broth (TSB). How many grams of TSB powder are needed? (TSB: $$30$$ grams per $$1000 ml)$$

$$1.8$$ grams$$\ (12 \times 5 = 60\ ml;\ \frac{30}{1000} \times 60 = 1.8\ grams)$$

Question 1

Which of the following statements best explains why agar is preferred over gelatin as a solidifying agent in microbiological media?

Accepted Answer

Agar remains solid at incubation temperatures because it solidifies at approximately $$42^\circ C$$ and does not melt until $$100^\circ C$$, unlike gelatin.

Question 2

You are preparing 20 agar deeps, each requiring 15 ml of Trypticase Soy Agar (TSA). How many grams of dehydrated TSA powder are needed to make the required volume? (TSA: $$40$$ grams per $$1000 ml)$$

Accepted Answer

$$12.0$$ grams$$\ (20 	imes 15 = 300\ ml;\ \frac{40}{1000} 	imes 300 = 12\ grams)$$

Question 3

Which sterilization method is most appropriate for sterilizing heat-sensitive solutions such as enzyme preparations?

Accepted Answer

Filtration using a membrane filter with a pore size of $$0.22\ \mu m$$

Question 4

A student needs to prepare 10 slants, each with 10 ml of Trypticase Soy Agar (TSA). How much TSA powder should be weighed out? (TSA: $$40$$ grams per $$1000 ml)$$

Accepted Answer

$$4.0$$ grams$$\ (10 	imes 10 = 100\ ml;\ \frac{40}{1000} 	imes 100 = 4\ grams)$$

Question 5

Which of the following best describes the function of the autoclave in microbiological media preparation?

Accepted Answer

It uses moist heat under pressure to sterilize media by killing all living organisms, including spores.

Question 6

A laboratory technician needs to sterilize a batch of glass petri dishes and metal forceps. Which sterilization method is most appropriate?

Accepted Answer

Dry heat in an oven at $$170^\circ C$$ for 2 hours

Question 7

Which of the following is a limitation of using ultraviolet (UV) light for sterilization in a microbiology laboratory?

Accepted Answer

UV light is effective only on surfaces and does not penetrate well, limiting its use to exposed areas.

Question 8

A student is preparing 12 broths, each requiring 5 ml of Trypticase Soy Broth (TSB). How many grams of TSB powder are needed? (TSB: $$30$$ grams per $$1000 ml)$$

Accepted Answer

$$1.8$$ grams$$\ (12 	imes 5 = 60\ ml;\ \frac{30}{1000} 	imes 60 = 1.8\ grams)$$

Question 9

Which of the following best distinguishes sterilization from disinfection?

Accepted Answer

Sterilization kills all living organisms, including spores, while disinfection kills only vegetative cells.

Question 10

A researcher needs to convert a temperature of $$95^\circ F to $$Celsius for an experiment. What is the correct Celsius temperature?

Accepted Answer

$$35^\circ C$$ $$\left(\frac{95-32}{1.8} = 35\right)$$

Question 11

Which of the following is the correct procedure for preparing a broth medium?

Accepted Answer

Add dry medium to water in a beaker, stir with a glass rod, and dispense into small test tubes.

Question 12

A solution of Trypticase Soy Broth (TSB) is not homogenized before dispensing into tubes. What is the most likely consequence?

Accepted Answer

The concentration of nutrients will vary between tubes, potentially affecting microbial growth.

Question 13

Which of the following is a correct statement about the use of membrane filtration in sterilization?

Accepted Answer

Membrane filtration is suitable for sterilizing heat-sensitive fluids such as serum.

Question 14

A laboratory is preparing 25 agar slants, each requiring 10 ml of TSA. How much TSA powder is needed? (TSA: $$40$$ grams per $$1000 ml)$$

Accepted Answer

$$20$$ grams$$\ (25 	imes 10 = 250\ ml;\ \frac{40}{1000} 	imes 250 = 10\ grams)$$

Question 15

Which of the following best explains why it is important to measure water with a graduated cylinder rather than a beaker when preparing media?

Accepted Answer

Graduated cylinders provide more accurate volume measurements than beakers.

Question 16

A microbiologist needs to sterilize a solution that cannot be heated above $$40^\circ C. $$Which method should be used?

Accepted Answer

Filtration through a $$0.22\ \mu m$$ membrane filter

Question 17

A student is preparing 18 broths, each with 5 ml of TSB. How many grams of TSB powder are required? (TSB: $$30$$ grams per $$1000 ml)$$

Accepted Answer

$$2.7$$ grams$$\ (18 	imes 5 = 90\ ml;\ \frac{30}{1000} 	imes 90 = 2.7\ grams)$$

Question 18

Which of the following is NOT a correct match between sterilization method and its typical use?

Accepted Answer

Incineration: sterilizing heat-sensitive solutions

Question 19

A laboratory technician needs to convert $$60^\circ C to $$Fahrenheit. What is the correct Fahrenheit temperature?

Accepted Answer

$$140^\circ F$$ $$\left(1.8 	imes 60 + 32 = 140ight)$$

Question 20

Which of the following is a critical step to prevent clumping when preparing agar media?

Accepted Answer

Add the dry medium slowly to the water with moderate stirring.

Preparation and Sterilization of Broth and Agar Media

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