Level C
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light and 12 hours of darkness (mixed), and 24 hours of darkness (dark). This covers the extreme cases
and one in the middle.
With the help of a teacher, the class decided to use plastic bags as growth chambers. The plastic bags
permit the students to observe and measure the germination of the seeds without disturbing them. Two
layers of moist paper towels were put into a clear plastic bag, with a line stapled about 1/3 of the way from
the bottom of the bag (see Figure 6) to hold the paper towel in place and to provide a seam to hold the
radish seeds.
One hundred and twenty seeds
were available for the study. The
size of the growth chambers
allowed for only 30 seeds. The
class decided to make use of the
extra seeds and create four growth
chambers, with one designated
for the light treatment, one for
the mixed treatment, and two for
the dark treatment. Thirty of the
seeds were chosen at random and
placed along the stapled seam of
light treatment bag. Thirty seeds
were then chosen at random
from the remaining 90 seeds and
placed in the mixed treatment
bag. Finally, 30 of the remaining
60 seeds were chosen at random
and placed in one of the dark
treatment bags. The final 30 seeds
were placed in the other dark treatment bag. The students were careful to make the growth chambers as
close to identical as possible. With two growth chambers for the same condition, these results could be
compared to ensure similar handling. After three days, the lengths of radish seedlings for the germinating
seeds were measured and recorded in millimeters.
The data were initially recorded in a summary format similar to that shown in Table 4, which shows
the sorted values. There were seeds in each of the treatment types that did not germinate, and these
were recorded with an “x” and are considered missing values. Thus, there are a total of 114 observations
(28 for Light, 28 for Mixed and 58
for Dark). Level C students should
be encouraged to discuss whether
omitting the seeds that did not
germinate could add bias to the
conclusions. Here it was decided that
because roughly the same number
of seeds failed to germinate in each
category, the missing values likely
happened “by chance,” and thus
Figure 6: Seed experiment growth bag for 30 seedlings
Table 4: Radish Seedling Lengths After 3 Days (sorted)
Treatment Type Seedling Lengths (mm)
1-Light x,x,2,3,5,5,5,5,5,7,7,7,8,8,8,9,10,10,10,10,10,
10,10,10,14,15,15,20,21,21
2-Mixed x,x,3,4,5,9,10,10,10,10,10,11,13,15,15,15,17,20,20,20,20,20,21,
21,22,22,23,25,25,27
3-Dark x, 5, 8, 8, 10, 10, 14, 15, 15, 15, 20, 20, 20, 20,20,22,25,25,25,25,
26,30,30,35,35,35,35,36,37,38
3-Dark x,5,8,8,10,10,10,11,14,15,15,15,16,20,20,20,20,20,24,25,29,30,
30,30,30,31,33,35,35,40