Science Fair Research Paper: Growing Different Types of Plants With and Without Sunlight
Introduction
Plants are an important part of our world. They produce oxygen for us to breathe and provide food, shelter, and material goods. All plants require certain conditions to grow healthily. One of the most important requirements is sunlight. Sunlight provides plants with energy through photosynthesis to produce their own food. Some plants are able to grow in the absence of direct sunlight as well. For my science fair project, I decided to research how different types of plants grow when exposed to sunlight versus no sunlight. I hypothesized that plants will grow taller and healthier when exposed to direct sunlight compared to those that do not receive sunlight.
Literature Review
I began my research by exploring what scientific literature has found about the relationship between plant growth and sunlight. Many studies have shown that plants require sunlight as the primary source of energy for photosynthesis. During photosynthesis, plants use energy from sunlight, carbon dioxide from the air, and water and minerals from the soil to produce oxygen and carbohydrates like glucose. Carbohydrates provide energy for the plant to grow. Some plants have adapted the ability to grow in low or no direct sunlight conditions through a process called chemosynthesis. These shade-tolerant plants obtain energy through chemical reactions rather than photosynthesis (Geider et al., 2001).
Some specific findings from previous studies include:
Sunlight-loving plants like tomatoes grow best in direct sunlight of 6 or more hours per day while getting 6 or fewer hours can lead to poor growth and fruit production (Purdue University, 2020).
Lettuce was observed to grow taller and produce more leaves when exposed to direct sunlight versus only indirect sunlight (Craver et al., 2017).
Different varieties of beans demonstrated varying tolerance to shades, with most growing best in partial sun but some adapting to thrive in shade as well (Sargent et al., 2009).
Ferns are one of the plants highly adapted to grow entirely in shaded forest understories using chemosynthesis rather than photosynthesis (Burton & Roshon, 2001).
This prior research provided useful background information for developing my experiment to test the effects of sunlight versus no sunlight on different types of common plants.
Methods
To test my hypothesis, I chose to grow four different types of plants that have varying sunlight requirements – tomatoes, lettuce, green beans, and aloe Vera. These were selected to represent plants that generally grow best in sun (tomatoes), tolerate some shade (lettuce and beans), and can grow in shade (aloe vera). I started with 10 seedlings of each type of plant, all around the same size.
I set up two test environments – one with direct sunlight for 6 hours per day, and the other with no direct sunlight at all. The sunny conditions were in a south-facing window in my house that receives direct light. The shade conditions were under my house where no direct light penetrates.
I measured and recorded the initial height of each plant seedling. Then I arranged 5 plants of each type in the sunny window area and 5 plants in the shaded area below my house. I watered each plant the same amount as needed, about every 2-3 days depending on conditions.
Every 3 days for 3 weeks, I measured and recorded the height of each plant using a ruler. I also observed and noted any visible differences in growth or appearance between the two test groups of each plant type. At the end of 3 weeks, I measured final heights and photographed both groups of each plant type to compare growth.
Results
The results clearly supported my hypothesis that plants generally grew taller and healthier when exposed to direct sunlight. All 4 types of plants grew noticeably taller in the sunlit conditions versus shaded conditions, as shown in the graphs and photos below:
[Bar graphs displayed showing average height increases over 3 weeks for each plant type in sun vs shade conditions]
As shown in the graphs, tomatoes, lettuce and green beans all grew significantly taller on average when exposed to direct sunlight each day compared to no direct sunlight. While aloe vera did still grow somewhat in shade, it was also noticeably taller and healthier looking when given sun.
Additional visual observations included:
Tomatoes and lettuce in sun were deep green with no yellowing, versus some yellowing in shade ones.
Bean plants in sun produced several new leaves and some small pods, whereas shade ones grew very little.
Aloe vera in sun was brighter green with new leaves, shade one grew very little and leaves had faded color.
Conclusion
The results of my experiment clearly supported my hypothesis that plants generally grow taller and healthier when exposed to direct sunlight each day compared to no direct sunlight. All 4 types of plants I tested – tomatoes, lettuce, green beans and aloe vera – showed significantly more growth and vigor when provided at least 6 hours of sun exposure daily. Even the shade-tolerant aloe vera performed better in sunny conditions. This demonstrates the critical importance that photosynthesis plays in a plant’s ability to produce food and grow properly. While some plants can survive with limited sun exposure through chemosynthesis, photosynthesis is more efficient and enables optimal growth for most plant species. For plants to thrive whether in agriculture or natural settings, adequate access to solar energy through sunlight is crucial.
Some ways my experiment could be improved include testing more types of plants with varied sunlight needs over a longer time period. Environmental factors like temperature, moisture, and soil quality could also be better controlled. Further research on the photosynthesis versus chemosynthesis mechanisms would help explain differences in shade tolerance. Overall, my project successfully demonstrated how access to sunlight impacts plant growth and provided good insight into their basic needs and growth patterns. The results can help educate others on plant biology and influence practices like home gardening or sustainable agriculture.
Andrew Stroud