Question

Write an activity to show that light is essential for photosynthesis.

Answer 1

Role of stomata during the process of photosynthesis: They are responsible for gaseous exchange required for the purpose of photosysthesis. 

Requirements : A potted plant, black paper, alcoho, papaer clips, beakers, iodine solution, water bath. 

Procedure : 

(1) Place a potted plant in dark for 72 hours for destarching. 

(2) Attach a light proof black paper strips on both sides of the leaf with the help of paper clips as shown in the figure. 

(3) Place the plant in sunlight for 3-4 hours. Pluck the experimental leaf, remore black paper strips. 

(4) Perform starch test by boiling leaf first in boiling water followed by boiling in alcohol over a water bath and then rinsing with cold water and again placing it in iodine solution. 

Observation : Only that portion of the leaf changes into blue-black which was not covered. The covered portion of the leaf does not give starch test. 

     

Conclusion : The covered portion of leaf was not receiving any sunlight. Hence, no photosynthesis occurred in that portion and no stach was formed. Due to this reason, only uncovered portion showed the starch test and not the covered portion. 

Result : The above experiment shows that sunlight is necessary for photosynthesis. 


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Answer 2

Answer:

1. To de starch the leaves, take the potted plant and place it in a dark area for two to three days.

2. Place the black paper strip over a portion of one of its leaves. Be sure to completely enclose the leaf on all sides.

3. Now leave this plant in the sun for three to four hours.

4. Remove the black paper covering the chosen covered leaf by plucking it.

5. Place this leaf in the water-filled beaker and bring to a boil for 10 minutes.

6. Remove the leaf, then boil it in alcohol for 10 minutes over a water bath. Thus, the chlorophyll is eliminated.

7. Remove the leaf and wash it in the sink.

8. Put a few drops of the iodine solution on this leaf and set it in the Petri dish. Now look at how the hue has changed.

• Observations:

1. With the exception of the area covered, the leaf turns blue-black.
2. Photosynthesis was not possible because this area was covered and did not receive light.
3. As a result, no starch was produced there. Due to photosynthesis, light entered the exposed area, where it was used to create starch.

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