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.

Ithink that b is correct but just in case wait to see if someone else answers

answer: carbon 14 can only be used to determine the age of the organisms that were once living, and igneous rocks are non living.

explanation:

carbon 14 dating is used to determine the age of the sample by estimating the amount of carbon 14 present in the sample and then comparing it with a reference standard.carbon 14 is a isotope of carbon which is radioactive and unstable. carbon 14 is assimilated by all plants and animals throughout their life from carbon dioxide. however, one the organisms die they stop this assimilation and the carbon 14 content starts to decrease.by knowing how much of carbon 14 is left in an organism after his death, one can estimate the age of the organism. the materials whose age can be estimated by carbon 14 method are the organic compounds. however, some inorganic compounds such as aragonite   shell can also be dated.however, if we consider the igneous rocks it is a non living component which never accumulated carbon 14 in it and thus, we cannot use carbon 14 dating method to estimate its age.