Journal of Academic Development and Education JADE Issue 9 | Page 26

26 | JADE
ARTICLE #2 | 27
L. A. ROBINSON
aids students understanding of concepts, the two working in unison
could motivate students when introducing a new topic or task and
help them to visualise the concept they are being presented.
Many courses within Biological and Forensic Sciences include a core
first year module on Genetics which in itself may be challenging
to teach due to the wide variation of capabilities within the class
and perhaps large class sizes in which material is being delivered.
In addition to lecture material, the practical aspect of prescribed
genetics modules may include standard procedures, some of which
have now been introduced at a further education level due to the
advancement of technologies. Because of this familiarity with
some techniques (even if only encountered briefly) it may result in
student’s disengaging these practicals as it isn’t ‘new’. Within the
practical aspect of a Genetics module, students are often taught how
to use pipettes appropriately but it is frequently seen throughout the
programme that students present samples for analysis which have
not been accurately transferred. A new approach was therefore taken
to specifically address this issue with first year students through a
novel exercise.
Methods & Materials
In an effort to demonstrate to students how inaccurate pipetting
effects a sample, and to test students ability to perform multiple
transfers accurately, the water problem sequence seen in Die Hard
with a Vengeance (McTiernan & Tadross, 1995) similar to Luchin’s
water jar problem, was transferred to the laboratory environment to
demonstrate pipetting accuracy. In the chosen movie sequence, our
lead characters are presented with two empty containers (a 3 gallon
jug and a 5 gallon jug) as well as a briefcase found at a water feature.
Opening this briefcase activates a bomb which can only be disarmed
by placing exactly 4 gallons of water on the scale within the case.
In order to do this the 5 gallon jug is filled and transferred to the 3
gallon jug leaving 2 gallons. The 3 gallon jug is then emptied and the
remaining 2 gallons placed inside. The 5 gallon jug is then refilled and
poured into the 3 gallon jug of which only 1 gallon will be transferred;
this therefore leaves 4 gallons in the 5 gallon jug which is placed on
the scale to deactivate the bomb. This clip is played to the students
and they are asked if they know how to solve the water problem
before the answer is outlined in full to the class as the solution is not
given away in the movie.
Scaling this problem down for the laboratory, it is highlighted to
students that 1ml of water weighs 1g and therefore we can use this
measurement to identify the accuracy of pipetting by weighing the
sample once transferred. The same scenario is presented to students;
that they must disarm a bomb by placing accurate volumes of water
TRI-HARD PIPETTING:
DEMONSTRATING PIPETTING ACCURACY USING DIE HARD WITH A VENGEANCE
onto a scale. At the front of the class, the closest student is asked
to open a briefcase of which wires trail out of the sides and appear
to attach to the underside of the weighing balance. On opening, the
briefcase contains plastic explosive labelled ‘C4’ (made from white
modelling clay) which they must deactivate.
Each group is given a 2ml, 1.5ml, and 0.5ml tube, a pipette set to
200µl, and a set of instructions. Their starting volumes are 500µl
in the 2ml tube, 1000µl in the 1.5ml tube and an empty 0.5ml. They
must finish with 600µl in the 2ml tube, 700µl in the 1.5ml tube and
200µl in the 0.5ml tube. There is an intentional use of the terms ml
and µl as students should be comfortable with this conversion and
understand the volumes within each; it also slightly obscures the
solution to the problem. When placed on the scale using empty
tubes to tare before each weighing, their code must therefore be
0.000 – 0.200 – 0.000 – 0.600 – 0.000 – 0.700 as the volumes are
weighed in succession. It has been found that adding a small volume
of food colouring to the water sample has a negligible effect on the
weight of the solution and can therefore be used to make transfer
more visual. Due to some inaccuracies between the weights of
different tubes and accuracy of pipettes used for teaching purposes,
an error rate of ±0.020 is acceptable in this exercise.
Students may only use the 200µl pipette provided and all sides
of the tubes to be used are covered using a black marker pen so
that volume scales cannot be used (as these should never be relied
upon). They can therefore only use the top volume presented on the
scale (though not required) and their 200µl pipette to transfer the
solution. The exercise takes 30–45 minutes based on a class size of
~50 students and a slide with instructions is provided via PowerPoint
(see Figure 1), the full associated presentation can be found on
slideshare at https://www.slideshare.net/DrLouiseRobinson. At
University of Derby this exercise is undertaken 4 times for a practical
circus and students are asked not to reveal the answer of the
exercise they are about to undertake to other students. Group work
is encouraged in order to promote teamwork with problem solving
in pairs or groups of which the size is not limited.
The majority of students choose to work with at least one other
person and occasionally a whole bench of students will come
together to solve the problem. Everyone theoretically works out the
solution and then discusses this with the group. When they believe
they have the correct answer students can then put it into practice
and are provided with the starting tubes. The answer is not checked
by any member of the teaching team; the weighing exercise will tell
them if they are correct. It is then up to students to either nominate
an individual in their group to do all transfers or students share the
responsibility and choose a section to transfer. When complete, the
tubes are then brought to a technician or demonstrator at the front