Ask A Scientist© Biology Archive

name         CHASE
status       student
age          11

Question -   HOW CAN I EFICTIVELY TEST THE EFFECTS OF LIGHT ON BREAD
MOLD?
-----------------------------------------------------
Hello Chase,
In order to test the effects of light on bread mould you need to set up an
experiment.  There are two things you need to have in your experiment to
make it a good experiment:
1. A 'control'.
2. Replicates

1. The 'control'
Obviously in order to test the effects of light on bread mold you will need
to actually shine some light on some bread mold and see what happens.  This
is your 'treatment'.

However, it is vitally important that you know what would have happened
without the treatment (in this case added light).  Let's pretend that you
do a test a you find that the bread mold under the light actually dies.
How do you know if your bread mold died because light was added or because
at that time of year all bread mold would die naturally or because by
adding light you caused the temperature to rise and that killed the bread
mold?  The answer is that you do not know unless you have taken the trouble
to find out with anouther test called the 'control'.  The 'control' is a
piece of bread mold, identical to the 'treatment' bread mold, which is
placed in identical conditions to the 'treatment' piece of bread mold
except that light is removed.  Your 'control' piece of bread mold will need
to be (to the best of your abillity) at the same temperature, in the same
area, at similar humidity, etc.  Part of the skill of designing a
scientific experiment is being able think of all the possible things which
might be affecting the bread mold and keeping them the same in both the
'treatment' and the 'control' (except, of course, for the presence of
light) so that when you find a difference between the 'treatment' and the
'control' you are sure that it is the result of the light rather than
something else.

2. Replication
Imagine you did got a piece of bread mold and shone a light on it...but you
had really bad luck and got some sick bread mold that was about to die
anyway.  You would conclude that light kills bread mold even though the
bread mold died bcause it was sick rather than because of the light.  If
you did the same thing with five bread molds you would have to be pretty
unlucky to get five sick bread molds.  That is why scientists repeat the
experiment to check that the results weren't just because of bad (or good)
luck.  Both the treatment and the control need to be repeated (replicated).

The experiment
To test whether light effects bread mold I would:
Set up two sets of five boxes.

One set of five boxes would have thick clear plastic on the top (to let
inthe light) and would contain pieces of bread with mold.

The other set of five boxes would have thick white plastic on the top (to
block the light) and would contain pieces of bread with mold.

I would put the boxes in a well lit room for a week and see what happens.
Make sure you don't let the bread and the bread mold dry out.

Good luck.

Cameron Millsom

__________________________
Cameron Millsom
Trinity Education Centre
University of Melbourne
Parkville, Victoria,  3052,  Australia

================================================================