Week 9: (ii) The Single Radial Diffusion
Test (Self and tutor assessed write up)
AIM: To quantify the interaction
of soluble antibody and antigen
LEARNING OUTCOMES:
To calculate the quantity of an
unknown antigen
To visualise the patterns of interaction
between antibody and antigen
In this experiment, you put different
concentrations of antigen into wells cut into gels containing different dilutions
of specific antibodies. You observed the differences in sizes of radial diffusion
rings around the wells and measured their diameter (d) under different conditions.
However, some students have been
experiencing difficulties manipulating their data.
Why do I need to plot the square
of d?
- This is because you are relating
your answer to an area - which is 2 dimensional rather than 1 dimensional.
Why do I need error bars?
- This is to estimate the variablitity
of the assay you have used. If it is not accurate - then how can you trust
the results? Statistics helps you to determine the amount of variablity, and
therefore the value of the result.
If my error bars are less than
1, they disappear when I square them - is this correct?
- Obviously not! If you have a diameter
of 5mm and a standard error of 0.5mm then the error is 10%. You need to calculate
the mean, upper and lower limits of error - and square these values.
- ie 4.5mm, 5mm and 5.5mm will become
20.25mm2, 25mm2 and 30.25mm2. So the error
of 10% in mm (5 plus or minus 0.5) has doubled to 20% in mm2 (simply
put 25 plus or minus 5- remember 10% of 25 is 2.5....).
Go back to your first write up to
remember what standard deviation, standard error and 95% confidence really means.