Investigating Environmental Effects—My Experiments on Photosynthesis & Respiration Rates

 

To truly understand these pathways, I investigated how environmental factors alter rates:

• Light intensity: I shone lamps at 200, 400, and 800 lux onto leaf discs and plotted the rate of floating discs. Rate plateaued at the light saturation point.
• Temperature: Using water baths at 10 °C, 25 °C, and 40 °C, I measured CO₂ release from yeast (model for respiration). Optimal respiration peaked at 25 °C; high heat denatured enzymes.
• CO₂ concentration: Varying sodium bicarbonate levels in pondweed experiments showed a proportional rise in O₂ bubble count up to a saturation level.

Plotting my data on graphs helped me grasp limiting factors and the concept of saturation points in KSSM.

Sample SPM Question
“Design an experiment to investigate the effect of light intensity on the rate of photosynthesis in aquatic plants. Include control variables and explain how you would collect and present your data.”

My design summary:
• Use identical pieces of pondweed in beakers with the same volume of water and CO₂ source.
• Vary light at set distances; keep temperature and CO₂ constant.
• Count O₂ bubbles over fixed intervals; repeat thrice.
• Plot rate (bubbles/min) versus light intensity.