#40 Photosynthesis investigations – chlorophyll, CO2, light tests

 Investigations to see if chlorophyll, light and CO2 are needed for photosynthesis. 

1. Chlorophyll is necessary for photosynthesis

Process

• Take a potted plant with variegated (green and white) leaves.
• Destarch the plant by keeping it in complete darkness for about 48 hours.
• Expose the plant to the sunlight for a few days.
• Test one of the leaves for starch with iodine solution.

Observations

     - Areas with previously green patches test positive (turn blue black).

     - Areas with previously pale yellow patches test negative (remain brown). 

Conclusion

   - Photosynthesis takes place only in green patches because of the presence of chlorophyll. 

   - The pale yellow patches do not perform photosynthesis because of the absence of chlorophyll.

2. Light is essential for photosynthesis

Process 

• Take a potted plant.
• Destarch the plant by keeping it in complete darkness for about 48 hours.
• Test one of it leaves for starch, to check that is does not contain any.
• Fix a leaf of this plant in between two strips of a thick paper on leaf.
• Place the plant in light for a few days.
• Remove the cover from the leaf and test it for starch.

Observations

Positive starch test will be obtained only in the portion of the leaf exposed to light and negative test in parts with paper strip.

Conclusion

Light is necessary for photosynthesis.

3. Carbon dioxide is essential for photosynthesis 

Process

• Take two destarched potted plants.
• Cover both the plants with bell jars and label them as A and B.
• Inside Set-up A, keep NaHCO₃ (sodium bicarbonate). It produces CO₂.
• Inside Set-up B, keep NaOH (Sodium hydroxide). It absorbs CO₂.
• Keep both the set-ups in the sunlight at least for 6 hours.
• Perform the starch test on both of the plants.

Observations

Leaf from the plant in which NaHCO₃ has been placed gives positive test.

Leaf from the plant in which NaOH has been kept give negative test.

Conclusion

Plant in Set up A gets CO₂ whereas plant in Set-up B does not get CO₂.

It means CO₂ is must for photosynthesis.

Source: mastermindtutor.com