Essay about mrs alex

Submitted By alex123witt
Words: 699
Pages: 3

Help Sheet 1.1
Analysing hair
Hair is often left at crime scenes and can be valuable evidence. The structure of hair can be examined under a light microscope.
Examining the internal structure of hair
You are going to make temporary slides of one of the hair samples you collected as evidence and examine them under a microscope.
You will need: hair evidence from the crime scene control hairs hair from four or five suspects clean microscope slide and cover slip access to microscope glycerol Pasteur pipette
(optional) digital camera with means to print photographs
(optional) eyepiece graticule clear plastic ruler
Microscopy method to make a drawing or take a photograph:
1 Complete a Risk Assessment on this piece of evidence before you analyse it. Use Task Sheet 1.1 to record the risks. Get your Risk Assessment checked by your teacher for each piece of evidence before you start to examine it.
2 Put the strand of hair to be examined on a clean microscope slide (remove any lifting tape first). The piece you use should include the root.
3 Place 1 or 2 drops of glycerol on the hair.
4 Gently lower a cover slip onto the hair, taking care to avoid trapping any air bubbles.
5 Examine the hair at x100 magnification.
6 Locate the hair root. Record its structure by drawing or photographing it. You can use the diagram of hair structure overleaf to help you.
7 View the rest of the hair at a magnification of x400. Record and label the hair. Indicate on the diagram the magnification you used to view the hair. Look for the layers that make up the hair, the colour of the hair and the presence of pigment granules.
8 Also examine and record hairs using this method from controls and suspects.
Help Sheet 1.1
Analysing hair (continued)
Microscopy methods to calculate width and medullary index of hair:
1 If you have an eyepiece graticule, calculate the actual width of the hair. Alternatively, place a clear plastic ruler on the stage of the microscope to find the diameter of the field of view. You can find the width of the hair by estimating the proportion of the field of view it fills.
2 Measure the width of the medulla and calculate the medullary index using the equation:

medullary index = width of the medulla width of the hair

The structure of hair

Help Sheet 1.1
Analysing hair (continued)
Identifying the origin of hair
The structure of hair, in particular the structure of the medulla, is useful in identifying the type of mammal to which the hair belonged.

human cat

fox red deer

rabbit sheep

Magnification: x300
Help Sheet 1.1
Analysing hair (continued)
Identifying scale patterns of hair
In humans, the scales that make up the cuticle of the hair overlap smoothly. In other mammals, the way the scales overlap creates a rougher