Question

 

1) You found a hair at a crime scene that is 10 inches long with the root torn off. If the medulla is 70% of the shaft and measures ~40microns, what is the approximate total volume of the hair in μm^3?

2) Being an adept forensic scientist, you are skilled in the art and efficiency of the serial dilution. Given the scenario in question 1, how would you use serial dilution to prepare the same

dilutions described: 1:10, 1:100, 1:1,000, 1:2,000, and 1:10,000?

Answer 1

The first line is scary :P

1. length of the hair = 10 inches = 0.254 m

2. 70% of the hair dia is medulla = 40 microns = 4 X 10^-5 m

let D be the dia of the hair, 70 % of D = 40 micron

by calculation 0.70 X D = 4 X 10^-5 m

D = 5.714 X 10^-5 m

Volume of the hair = = { X (5.714 X 10^-5 )² X 0.254}/ 4

V = 6.51 X 10^-10 m3 = 6.51 X 10⁸

2. Steps how you can prepare the mentioned dilutions:

A ) Determine the proper dilution liquid you want to use

B) prepare 5 testubes with marking 1:10, 1:100, 1:1,000, 1:2,000, and 1:10,000 and fill them each with 9 ml of dilution liquid

let 1:10 - test tube 1

1:100 - test tube 2

1:1,000 - test tube 3

1:2,000 - test tube 4

and 1:10,000 - test tube 5

C) Now take 1 ml of undiluted sample using a micropiptte and pour it in test-tube 1

D) For the second serial dilution, you will take 1 mL of solution from test-tube 1 and add it to the 9 mL of dilution liquid in the tube 1:100, i.e test-tube 2.

E) For the 3rd serial dilution, you will take 1 mL of solution from test-tube 2 and add it to the 9 mL of dilution liquid in the tube 1:1000, i.e test-tube 3.

F) For the 4th serial dilution, you will take 2 mL of solution from test-tube 2 and add it to the 9 mL of dilution liquid in the tube 1:2000, i.e test-tube 4.

G) For the 5th serial dilution, you will take 1 mL of solution from test-tube 3 and add it to the 9 mL of dilution liquid in the tube 1:10,000, i.e test-tube 5.

Note: you have to dissolve the hair strand in a suitable reagent off course.