Problem:
What effect does sunlight have on plant growth?
Background Information:
Photosynthesis is the process by which plants capture light energy and use it to make
food. The chemical formula for photosynthesis is as follows: 6CO2 + 6H2O
C6H12O6 + 6O2 (Pearson, Chris). This process occurs most often in the chloroplast of
green leaves. Chloroplasts contain a green pigment called chlorophyll that captures light
energy. Plants can only carry out photosynthesis in the present of light energy. This is
critical to plant growth because plants need energy to fully develop and survive.
Previous studies have shown that plants grown under direct sunlight grew taller and fuller
than plants that have been grown without sunlight. Furthermore the plants grown without
direct sunlight actually died because of the lack of energy produced from photosynthesis
(Irwin, 9). Another study has also demonstrated that the difference between artificial
light and sunlight has no effect on plant growth (James, Stephen).
Hypothesis:
If bean plants are planted and grown with varying amounts of light then the bean plants
that spend the greatest amount of time in the light will grow the tallest because
photosynthesis only occurs in the presence of light energy.
Materials:
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Nine bean seeds
Three planting pots
Soil
Water
Growing lights
Window
Closet
Permanent marker
Masking tape
Ruler / Meter stick
Pens/Pencils
Procedure:
1. First gather the three planting pots, tape and permanent marker. Use tape and
permanent marker to label one pot Control, one pot Light and one pot Dark.
2. Fill the Control pot with soil until it is 5cm from the top.
3. Using finger, make three holes about 2cm deep into the soil. Space holes evenly
throughout the pot so that each bean plant has room to grow.
4. Place one bean seed in each hole and cover the bean seed with soil.
5. Repeat steps 1-4 for the Light and Dark pots.
6. Water each pot. Make sure that each pot receives the same amount of water.
7. Place the Control pot on the windowsill, the Light pot under the growing lights, and
the Dark pot in the closet. Keep the pots at this location for the next three weeks.
8. For the next three weeks, water each pot once a day and observe growth of the plants.
9. After the three week period, observe and record the appearance of the plants in each
pot.
10. Next use a meter stick to measure t plant growth in centimeters of all three bean
plants in each pot.
11. Record plant growth in data table and calculate the average plant growth for each pot.
Data:
Figure 1: Average Plant Growth
Plant
Group
Plant 1
Final Growth
Plant 2
Final Growth
Plant 3
Final Growth
Average Plant
Growth
Control
10cm
10cm
10cm
10cm
Light
15cm
15cm
15cm
15cm
Dark
5cm
5cm
5cm
5cm
Figure 1 shows the average growth of Control, Light and Dark plant groups over a three week
period.
Calculations:
1. Plant 1 Average Growth: (10cm + 10cm + 10cm) / 3 = 10cm
2. Plant 2 Average Growth: (15cm + 15cm + 15cm) / 3 = 15cm
3. Plant 3 Average Growth: (5cm + 5cm + 5cm) / 3 = 5cm
Observations:
1. Control Group: Green Plants; 3-5 pods per plant
2. Light Group: Green Plants; 3-5 pods per plant
3. Dark Group: Pale Yellow Plants; No pods developed
Figure 2: The Effect of Light on Plant Growth
Average Plant Growth
(cm)
The Effect of Light on Plant Growth
16
14
12
10
8
6
4
2
0
Control
Light
Dark
Plant Group
Figure 2 shows the average growth of Control, Light and Dark plant groups over a three week
period.
Data Analysis:
After running the experiment for 3 weeks, it was found that the bean plant that was
placed in the sunlight for 24 hours grew tallest in height at 15cm. The control bean plant
and bean plant grown in the dark grew to 10cm and 5cm respectively. Based on this data,
the amount of sunlight does effect the growth of the plant. The more sunlight the plant is
exposed to, the greater the height of the plant.
Conclusion:
The initial prediction, “If bean plants are planted and grown with varying amounts of
light then the bean plants that spend the greatest amount of time in the light will grow the
tallest” is supported by the results. Plants require sunlight to perform photosynthesis.
Photosynthesis is the plants method of creating food for itself and food, in the form of
glucose, is essential for the plant’s survival. Without glucose, the plant does not obtain
the necessary energy required to carry out life processes. Therefore, a plant that receives
sun 24 hours a day is more likely to thrive than a plant that receives no light or only
partial sunlight.
To perform this experiment in the future, it would be important to make sure the pots are
at least 25.4 centimeters in diameter as competition among the plants could inhibit their
growth (in a smaller pot). It would also be beneficial to incorporate a greater range of
light exposure to see if perhaps a plant in 24 hours of sunlight would benefit the same
amount as a plant in 18 hours of sunlight.
Now that this experiment has been completed, it would be interesting to find out if
exposure to 24 hours of sunlight has an effect on different types of plants.
Work Cited