Experiment Date: October 15, 2023
Lab Partners: A. Scientist, B. Researcher
Instructor: Dr. Evelyn Reed

Introduction

Plants require sunlight for photosynthesis, a process converting light energy into chemical energy. This experiment investigates how varying durations of sunlight exposure affect the growth rate of Phaseolus vulgaris (common bean plants). We hypothesize that plants exposed to 8–10 hours of sunlight daily will exhibit significantly greater height and biomass compared to those exposed to 4 hours or less.

Materials and Methods

Materials:

• 30 identical bean seedlings (Phaseolus vulgaris)
• 3 growth chambers (controlled temperature: 22°C, humidity: 60%)
• Measuring tape (cm)
• Digital scale (g)
• Soil and fertilizer
• Timer
• Data logbook

Procedure:

1. Seedlings were randomly divided into three groups (10 plants/group):
   • Group A: 4 hours of sunlight/day (simulated via LED grow lights).
   • Group B: 8 hours of sunlight/day.
   • Group C: 12 hours of sunlight/day.
2. All groups received identical soil, water, and fertilizer.
3. Height and leaf count were measured weekly for 4 weeks.
4. Final biomass (dry weight) was recorded after drying plants at 70°C for 48 hours.

Results

Table 1: Mean Growth Metrics After 4 Weeks
| Group | Avg. Height (cm) | Avg. Leaf Count | Avg. Biomass (g) |
|-------|------------------|-----------------|------------------|
| A (4h)| 12.3 ± 1.2 | 8.1 ± 0.9 | 2.4 ± 0.3 |
| B (8h)| 24.7 ± 2.1 | 15.3 ± 1.2 | 5.8 ± 0.5 |
| C (12h)| 22.1 ± 1.8 | 14.0 ± 1.0 | 5.2 ± 0.4 |

Key Observations:

• Group B (8h) showed the tallest growth and highest biomass.
• Group C (12h) exhibited slight yellowing of leaves (chlorosis), indicating potential light stress.
• Group A (4h) had stunted growth and smaller leaves.

Discussion

Results support the hypothesis: Group B (8h sunlight) demonstrated optimal growth, aligning with photosynthetic efficiency studies (Smith et al., 2021). Group C’s reduced growth suggests excessive light can inhibit photosynthesis via photoinhibition (Jones, 2020). Group A’s poor growth confirms light limitation.

Limitations:

• Small sample size (n=10/group) may reduce statistical power.
• Light intensity was not measured; duration was the sole variable.

Conclusion

Sunlight duration significantly impacts bean plant growth. 8 hours of daily sunlight maximizes height, leaf development, and biomass. Longer durations (12h) may cause stress, while shorter durations (4h) severely limit growth. Future studies should vary light intensity and duration to refine optimal conditions.

References

1. Smith, J., et al. (2021). Photosynthetic Efficiency in Legumes. Journal of Plant Biology, 45(3), 112–125.
2. Jones, R. (2020). Light Stress in Crop Plants. Agronomy Today, 12(4), 78–90.

End of Report
Note: This report is a fictional example for educational purposes only.