Douglas County High School: Sample Scientific Investigation Write-Up
Title: The effect of light intensity on the growth of radish plants.
Problem:
OR
To determine if radish plants grow taller in the dark or with sunlight.
How does light intensity affect the growth of radish plants?
Hypothesis: If the intensity of light is decreased, then the radish plants will not grow as tall because
light is necessary for photosynthesis, which allows plants to grow.
Independent Variable: Level of light (Watts)
Dependent Variable: Height of the plants (cm)
Constants (Controlled Variables):
* Radish type: Different seeds grow differently
* Amount of water: Water affects plant growth
* Type of pot: Shape and material can affect plant growth
* Type of soil: Soils have different nutrients
* Time: Length of experiment can alter plant growth
* Temperature: Affects plant growth
* Amount of soil: Soil can affect plant growth
Control:
Radish grown in 100W.
Procedure:
Materials:
• 12 Radish plants
• metric ruler
• 100 mL graduated cylinder
•
Light sources: 25W bulb, 60W
bulb, 100W bulb
Steps:
1. Determine the height of all radish plants (in centimeters) from dirt level to tallest
point and record in data table #1.
2. Place three radish plants in the dark.
3. Place three radish plants under 25W bulb.
4. Place three radish plants under 60W bulb.
5. Place three radish plants under 100W bulb.
6. Water each plant with 200 mL of water once a week.
7. Every two days make the following observations:
 Record the height of all radish plants in Data Table # 1.
 Record any qualitative observations about general plant appearance in
Data Table # 2.
8. Continue watering plants and recording data for fifteen days.
Douglas County Scho…, 11/6/09 1:55 PM
Comment: Title includes the effect of the IV
on the DV
Douglas County Scho…, 2/22/10 1:53 PM
Comment: The problem includes both the
IV and its effect on the specific DV being
measured.
Scientific Inquiry Funk 2/22/10 1:54 PM
Comment: Define the purpose of the
investigation.
Scientific Inquiry Funk 1/22/10 1:22 PM
Comment: Formulate a testable hypothesis
and explain hypothesis using scientific
reasoning in “because” statement.
Scientific Inquiry Funk 1/22/10 1:27 PM
Comment: Increases reliability and
validity by keeping the same from trail to trial.
Douglas County Scho…, 11/6/09 2:13 PM
Comment: IV, DV, Constants and Controls
are clearly listed following the hypothesis.
Scientific Inquiry Funk 1/22/10 1:21 PM
Comment: Identifies relevant variables and
how to manipulate them.
Douglas County Scho…, 11/6/09 2:23 PM
Comment: Clearly identify all materials
used in the experiment.
Scientific Inquiry Funk 1/22/10 1:27 PM
Comment: Reliability and validity addressed
through multiple trials at each level of IV.
Douglas County High School: Sample Scientific Investigation Write-Up
Data & Observations:
Data Table #1: Radish Plant Height in Varying Amounts of Light (cm)
Plant
Day 1
Day 3
Day 5
Day 7
Day 9 Day 11
water
water
Dark #1
13
13.5
14.0
14.5
17.4
20.3
Dark #2
12.2
13.4
15.0
16.1
18.1
19.3
Dark #3
13.2
14.0
14.9
15.7
18.5
21.9
Ave. Dark
12.8
13.6
14.6
15.4
18.0
20.5
25W #1
12.5
12.5
12.9
13.4
13.9
14.5
25W #2
11.8
12.4
12.9
13.3
13.8
14.3
25W #3
12.0
12.3
12.9
13.2
13.8
14.5
Ave. 25W
12.1
12.4
12.9
13.3
13.8
14.4
60W #1
11.5
12.4
12.9
13.7
14.3
15.6
60W #2
12.3
13.0
13.8
14.5
15.2
15.9
60W #3
12.5
13.3
14.2
14.9
15.4
16.2
Ave. 60W
12.1
12.9
13.6
14.4
15.0
15.9
100W #1
10.3
10.5
11.0
12.3
15.3
16.2
100W #2
11.4
11.5
12.2
13.0
14.9
15.8
100W #3
11.5
11.7
12.5
13.4
13.5
15.7
Ave. 100W
11.1
11.2
11.9
12.9
14.6
15.9
Day 13
Day 15
21.9
22.1
23.0
22.3
14.9
14.7
15.1
14.9
16.2
16.7
17.0
16.6
18.2
16.7
17.3
17.4
25.1
24.5
26.3
25.3
15.5
15.0
15.2
15.2
17.3
17.5
18.1
17.6
20.1
19.9
21.7
20.6
Data Table #2: Average Plant Height in Varying Amounts of Light (cm)
Plant
Day 1
Day 3
Day 5
Day 7
Day 9
Day 11 Day 13
Dark
12.8
13.6
14.6
15.4
18.0
20.5
22.3
25W
12.1
12.4
12.9
13.3
13.8
14.4
14.9
60W
12.1
12.9
13.6
14.4
15.0
15.9
16.6
100W
11.1
11.2
11.9
12.9
14.6
15.9
17.4
Day 15
25.3
15.2
17.6
20.6
Data Table #3: Average Difference in Plant Height (cm) from Day 1 to Day 15
Plant
Day 1 Height (cm)
Day 15 Height (cm)
Difference (cm)
Dark
12.8
25.3
12.5
25W
12.1
15.2
3.1
60W
12.1
17.6
5.5
100W
11.1
20.6
9.5
FORMULA FOR CALCULATION: HeightF-HeightI = Difference in Height (cm)
Data Table #4: Rate of Growth in Differing Amounts of Light
Plant
Rate of Growth
(cm/day)
Dark
0.85
25W
0.21
60W
0.37
100W
0.63
RATE OF GROWTH CALCULATION: HeightF - HeightI = Rate (cm/day)
TimeF - TimeI
Processing Data Funk 1/22/10 1:55 PM
Comment: Organize and record data in a
table that is clearly titled, with labels and units.
Do NOT graph all of this data.
Communication in Sci…, 1/22/10 2:24 PM
Comment: Presents data appropriately for
the task.
Processing Data Funk 2/22/10 1:26 PM
Comment: Process data: calculate averages,
rates, % change etc. This is the only data that
you will graph!
•Table 2: Averages or mean of multiple trials
•Table 3: Difference in beginning and final
data
•Table 4: Rate calculation
Douglas County High School: Sample Scientific Investigation Write-Up
Data Table # 5:
Qualitative Data: Radish Plants Under Varying Amounts of Light
Day 5
Plant stem has grown
longer, color is slightly
faded, still turgid
Day 7
(water)
Plant continues to grow
taller, color fading
significantly
Same
Plants under 60W
Plant looks healthy, dark
green, turgid
Plant has grown more,
looks healthy, is turgid
and dark green
Plant has grown more,
leaves growing, looks
healthy, is turgid and
dark green
Same
Day 9
Plant extremely tall, few
leaves, color faded
Same
Same
Day 11
Plant seems to be
reaching for any light,
still turgid, faded color
Same
Same
Day 13
Long stem, no leaves
faded color
Same
Same
Day 14
Plant is light green in
color, still turgid, but no
overall growth has
occurred.
Same
Same
Day 1
(water)
Day 3
Graph:
Plants in Dark
Plant looks healthy, dark
green, turgid
Plant looks the same –
no change
Plants under 25W
Plant looks healthy, dark
green, turgid
Plant is growing some,
looks healthy, and is still
turgid & dark green
Same
Plants under 100W
Plant looks healthy, is
turgid and dark green
Plant has grown more,
looks healthy, is turgid
and dark green
Plant has grown more,
leaves growing, looks
healthy, is turgid and
dark green
Plant has more leaves,
broad leaves, growing
taller, is turgid and dark
green
Plant has more leaves,
broad leaves, growing
taller, is turgid and dark
green
Plant has more leaves,
broad leaves, growing
taller, is turgid and dark
green
Plant has more leaves,
broad leaves, growing
taller, is turgid and dark
green
Plant has more leaves,
broad leaves, growing
taller, is turgid and dark
green
Processing Data Funk 2/22/10 1:24 PM
Comment: Use appropriate graph for the
data (qualitative/quantitative = bar graph;
quantitative / quantitative = line graph)
•Graph processed data, NOT all data
•Include best fit lines/curves
•Follow all graphing guidelines (title, labels
(units), and key)
Communication in Sci…, 1/22/10 2:24 PM
Comment: Presents data appropriately for
the task.
Douglas County High School: Sample Scientific Investigation Write-Up
Data Analysis:
Plants grown with greater intensities of light grow taller than plants with lower intensities. Plants grown
in the dark are the tallest, but look the most unhealthy.
Conclusion:
The purpose of this lab was to investigate varying intensities of light on plant growth. The hypothesis
that lower intensities of light would result in shorter plants was partially supported by the data. Looking
at Data Tables #2, #3, and #4, the plants grown in the light showed the pattern predicted by the
hypothesis. At 25W, the average growth was 0.21 cm per day, while at 60W the plants grew an average
0.37 cm per day and at 100W the plants grew an average of 0.63 cm per day. At greater light intensities,
plants undergo greater amounts of photosynthesis, resulting in plants that grow larger. This corresponds
to what is known about photosynthesis, that more light results in greater amounts of photosynthesis
which means more growth. (Class Notes)
However, in the dark, the plants grew an average of 0.85 cm per day. This data does not support the
hypothesis. Referring to the research, the plants grown in the dark grew taller because hormones in the
plants allow the stems to grow rapidly while leaf growth is suppressed. This occurs so that plants can
reach light in order to photosynthesize better. Light triggers a change in the plant cells allowing the
stems and leaves to broaden in order to capture light for photosynthesis.
(http://www.kidsgardening.com/Dig/DigDetail.taf?ID=968&Type=Art)
One possible error was the placement of the plants in relation to the lamps, which may have resulted in
burning the leaves or being too far away from the plants and could have been prevented by a
predetermined safe placement distance.
Another possible error was an accidental exposure to light for the dark plants, which may have resulted
in skewed observations and could have been prevented by the teacher locking the closet doors.
A possible future investigation would be testing the color of light on plant growth.
Resources:
Luminous Lessons: Investigating Light (January 22, 2010)
http://www.kidsgardening.com/Dig/DigDetail.taf?ID=968&Type=Art
Processing Data Funk 1/22/10 2:01 PM
Comment: Explain patterns and trends in the
data.
Processing Data Funk 1/22/10 2:04 PM
Comment: This is not necessarily displayed
on the graph, but was recorded in qualitative
data.
Processing Data Funk 1/22/10 2:26 PM
Comment: Comment on the reliability of the
data.
Communication in Sci…, 1/22/10 2:23 PM
Comment: Communicates scientific
concepts correctly using appropriate language.
Communication in Sci…, 1/22/10 2:20 PM
Comment: Outside sources must be used
and referenced.
Processing Data RE-1 2/22/10 1:42 PM
Comment: Identify each weakness/error in
the lab, discuss how it may have affected the
lab, and suggest an improvement.
Communication RE-1 2/22/10 1:43 PM
Comment: Suggest further investigation for
the future.