1. You are given a 1 gram soil sample of unknown bacterial load. After doing 10-fold serial dilutions of the soil in sterile water, 100 uL volumes are taken from each dilution for preparation of pour plates. Following incubation, each half of the 10-8 plate has 46 colonies. a) What was the dilution factor?
b) How many bacteria were present in the soil?

2. Staphylococcus aureus divides every 20 minutes. A culture begins with 10 bacterial cells.
a) After 5 hours, how many generations have occurred
b) After 5 hours, how many bacteria are present?

3. How many milliliters would you need to prepare a 10-2 dilution from a 10ml starting culture?

1a. 1:10

1b. 4.6×10¹³

2a. 15generations

2b. 327,680

Explanation:

10 fold serial dilution means 1ml of stock is mixed in 9ml distilled water. This is called as 10⁻¹ solution.

In this way, take 1ml each of every dilution and mix in 9ml distilled water to make 10⁻², 10⁻²-------10⁻⁸ dilutions.

Now, CFU/ml = no. of colonies × dilution factor/ volume of sample plated.

b. lithosphere, asthenosphere, mesosphere   is the answer most likely

the corpus luteum secretes estrogens and progesterone. the latter hormone causes changes in the uterus that make it more suitable for implantation of the fertilized ovum and the nourishment of the embryo. if the egg is not fertilized, the corpus luteum becomes inactive after 10–14 days, and menstruation occurs.

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