Three grams of soil were added to 27 ml of sterile water and shaken vigorously. After the soil particles settled, 0.1 ml of this was added to 9.9 ml of sterile water. This was further diluted by 4 successive 1/10 dilutions. One ml from the last dilution was used to prepare a pour plate. After incubation, 289 colonies were present on this plate.
What was the number of colony-forming units/gram of the soil?

289 × 10 ⁷ colony-forming units/gram

Explanation:

Given that;

Three grams of soil were added to 27 ml of sterile water;  ----- Let that be A

We would notice from the above statement that 3 grams of soil that was added was equivalent to 1:10 dilution of the sample

After settling of soil particles;

0.1 ml of this was added to 9.9 ml of sterile water.------------- Let that be B

Furthermore,

4 successive 1/10 (1:10) dilutions takes place ------------- Let that be C

NOW, the total dilution we have = 10 ⁻⁷

The question proceeds by saying; One ml from the last dilution was used to prepare a pour plate and After incubation, 289 colonies were present on this plate.

∴ the  number of colony-forming units/gram of the soil =

=

=

= 289 × 10 ⁷ colony-forming units/gram

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

when atoms of different types of elements join together, they make molecules called compounds. water consists of compound molecules made up of 2 hydrogen atoms and 1 oxygen atom. this is why it's called h2o. water will always have 2 times the number of hydrogen atoms as oxygen atoms.