Miss Angler's Biology Class: Investigating Photosynthesis

Introduction

• Investigations and photosynthesis are challenging topics in exams.
• Objective: Simplify and break down the process of identifying variables, controls, validity, and reliability in photosynthesis investigations.

Key Investigation Topics

1. Is Light Needed for Photosynthesis?

   • Setup:
     • Use a pot plant, destarch it first for validity.
     • Attach foil or black paper to block light in certain leaf areas.
     • Allow the plant to photosynthesize in sunlight.
     • Conduct a starch test to observe changes.
   • Observations:
     • Yellow areas indicate no photosynthesis (covered by foil).
     • Blue-black areas indicate photosynthesis took place.
   • Dependent Variable: Presence of photosynthesis (not color change).

2. Matching Tests with Outcomes

   • Use color changes in leaves to determine where photosynthesis occurred.
   • Blue-black indicates positive for starch/photosynthesis.

3. How Does Light Intensity Affect Photosynthesis?

   • Setup:
     • Destarch plant.
     • Place pond weed in water with a lamp set at varying distances.
   • Measurement:
     • Count bubbles produced as an indicator of photosynthesis rate.
   • Variables:
     • Independent Variable: Light intensity.
     • Dependent Variable: Rate of photosynthesis (bubbles are indicators).
   • Control: Plant with no light to compare against.

Additional Investigation: Light Requirement

• Before and After Test Setup:
  • Destarch plant leaves and use an indicator liquid (hydrogen carbonate) which reacts to CO2 levels.
  • Control (Test Tube A): No leaf, shows no color change.
  • Test (Test Tube B): Leaf present, turns purple indicating CO2 decrease and photosynthesis occurrence.
  • Test (Test Tube C): Tin foil wrapped, turns yellow due to lack of light and increased CO2 from respiration.
  • Test (Test Tube D): Gauze wrapped, shows no change indicating balanced CO2 levels.

Variables in Experiments

• Independent Variable: Light presence/intensity.
• Dependent Variable: Photosynthesis occurrence/rate, not the color change.
• Control Experiment: Removing the light for comparison.

Conclusion

• Photosynthesis investigations have multiple variables and require careful interpretation of results.
• Suggested viewing of related videos on destarching and cellular respiration for comprehensive understanding.