BIO

• Chlorophyll is a green pigment needed for photosynthesis
• Chlorophyll is present in the chloroplast and absorbs light for photosynthesis
• Chlorophyll transfers light energy into chemical energy for the formation of glucose and other carbohydrates like starch, cellulose, and sucrose
• Starch:

  • Storage food material formed by plants
  • Composed of many glucose units
  • Accumulated in chloroplasts after photosynthesis
  • Presence of starch in a plant is evidence of photosynthesis
• Sucrose:

  • Transports food around the cell
• Cellulose:

  • Makes up the cell wall
• Starch would be used for storage
• Destarched plant:

  • Plant that has utilized all its stored starch
  • Unable to carry out photosynthesis due to lack of resources
• Destarching plant:

  • Necessary for experiments on photosynthesis
  • Place the plant in the dark for about six hours to deplete existing starch before conducting the experiment
• Starch test preparation:

  • Pluck a leaf from the plant
  • Heat the leaf in a water bath to break cell walls and expose pigments
  • Dip the leaf in hot alcohol to remove chlorophyll, causing the leaf to become colorless
  • Soften the leaf by dipping it in warm water
• How to perform starch test on a leaf:

  • Place the leaf in a petri dish and add iodine solution
  • Observe the color change, parts exposed to light will change color while parts not exposed to light will not
• Experiment to show that carbon dioxide is essential for photosynthesis:

  • Destarch the plant
  • Remove carbon dioxide by sealing part of the leaf with a glass bottle containing potassium hydroxide
  • Keep the setup in light for five hours
  • Conduct iodine/starch test, blue-black color indicates presence of carbon dioxide, no change in color indicates absence of carbon dioxide
  • Conclusion: Carbon dioxide is needed for photosynthesis