Question

how to prove co2 light and chlorophyll is required for photosynthesis​

Answer 1

Answer:

Explanation

Take two healthy potted plants which are nearly the same size. Keep them in a dark room for three days. Now place each plant on separate glass plates. Place a watch-glass containing potassium hydroxide by the side of one of the plants. The potassium hydroxide is used to absorb carbon dioxide. Cover both plants with separate bell-jars. Use vaseline to seal the bottom of the jars to the glass plates so that the set-up is air-tight. Keep the plants in sunlight for about two hours. Pluck a leaf from each plant.  Remove the green coloured chlorophyll from the leaves by boiling them in alcohol. Wash the decolourised leaves with water and then pour iodine solution over them. Observe the change in colour of the leaves.

We will find that the leaf from the plant (which was inside the bell jar containing potassium hydroxide which absorbed the carbon dioxide), does not turn blue-black on adding iodine solution showing that no starch is present. So we can conclude that the photosynthesis cannot be carried out without carbon dioxide.

The leaf from the plant (which was inside the other bell jar without potassium hydroxide and so having carbon dioxide in it) turns blue-black on adding iodine solution showing that starch is present in this leaf. From this observation we conclude that photosynthesis (to make starch) takes place in the presence of carbon dioxide.

So this shows that carbon dioxide is necessary for the process of photosynthesis to take place.

TO SHOW CHLOROPHYLL IS NECESSARY FOR PHOTOSYNTHESIS

First of all, we need to take a potted plant with variegated leaves like croton and keep it a dark region, away from sunlight for 3 days. This will halt photosynthesis and destarch the plant.

Next keep this plant in sunlight for 6-8 hours. The plant can now carry out photosynthesis and produce starch.

Next,luck a leaf from this plant and mark the green areas in it and trace them on a sheet of paper. Mark the regions as green and yellow. . As can be deduced, the green areas contain chlorophyll which is absent in the yellow areas.  

Next immerse the leaf in boiling alcohol so as to decolourise it. he leaf slowly loses its green color, which goes into the alcohol.Dip this decolorized leaf in iodine solution using a pair of forceps.   Now remove the leaf from iodine solution and rinse it in distilled water. Remove the leaf from distilled water and keep it on a petri dish. Two color regions are visible in the leaf. They are reddish brown and blue-black.Compare this leaf with the previously traced drawing on the graph paper. een parts of the tracing and blue-black regions of the leaf coincide. Similarly the reddish brown regions in the leaf coincide with the yellow areas on the traced figure. we can conclude that the earlier green parts of the leaf turn blue-black whereas the yellow parts have become reddish brown. Green parts of the leaf possess chlorophyll; hence they carry out photosynthesis and produce starch, which turns blue-black with iodine. The yellow regions of the leaf cannot carry out photosynthesis since they lack chlorophyll and hence no starch is produced here.

Answer 2

Answer:

• Chlorophyll is required for photosynthesis​:

1. Take a potted plant with colored leaves, such as a croton, and place it in a dim area out of the sun for three days. As a result, photosynthesis will stop, killing the plant.
2. Keep the plant facing the sun for 6 to 8 hours after that.
3. Now that photosynthesis is possible, the plant can also generate starch.
4. Mark the leaf's green regions, then trace them on a piece of paper. Mark the areas with green and yellow markers.
5. Chlorophyll is present in the green sections but not in the yellow ones.
6. To remove color, submerge the leaf in boiling alcohol. The leaf gradually loses its green hue, and the alcohol absorbs it.
7. This leaf has lost its color; soak it in iodine solution.
8. The leaf should now be taken out of the iodine solution and rinsed with distilled water. Keep the leaf on a petri plate after removing it from the distilled water.
9. Observation: The leaf has two distinct color zones. They are blue-black and reddish-brown.

• CO2 is required for photosynthesis​:

1. The following actions must be taken in order to demonstrate that carbon dioxide is required for photosynthesis.
2. A portion of a de starched plant's leaf should be placed into a conical flask containing potassium hydroxide.
3. Carbon dioxide gas from the air in the glass bottle is absorbed by potassium hydroxide solution.
4. Leave the plant in the sun.
5. Perform a starch test on this and another leaf of the same plant a few hours later.
6. Observation: Leaf exposed to air are bluish black in color. The hue of a leaf exposed to KOH does not turn blue-black.

• Light is required for photosynthesis​:

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 place it in the Petri dish. Now look at how the hue has changed.
9. Observations: With the exception of the area covered, the leaf turns blue-black. Photosynthesis was not possible because this area was covered and did not receive light. 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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