Question

write an activity to show CO2 necessary for photosynthesis

Answer 1

Here you go

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Starch would not be present in the plant(a) but it would be present in plant (b)

Hence we can conclude CO2 is essential for photosynthesis

Answer 2

Aim :
To show that carbon dioxide is necessary for photosynthesis.

Materials Required :
Two healthy potted plants of same size, two glass plates, two
bell jars, vaseline, watch glass, potassium hydroxide, alcohol,
spirit lamp and beaker.

Procedure :
1. Keep the potted plants in dark for three days, so that the
leaves are destarched.

2. Place the potted plant (a) on a glass plate and put a watch
glass containing potassium hydroxide (KOH) by the side of
the pot. Cover it with a bell jar.

3. Place the other potted plant (b) on second glass plate and
cover it with a bell jar.

4. Use Vaseline to seal the bottom of jars to the glass plates so
that the set up is air tight.

5. Keep the plants in sunlight for two hours.

6. Pluck a leaf from each plant and test the same
for the presence of starch.

Observation :
The leaf of plant (b) without potassium hydroxide
turns blue-black, while the leaf of plant (a) with
potassium hydroxide remains pale coloured or
colourless.

Conclusion :
This experiment demonstrates that the leaf of plant
(b) has synthesised starch by photosynthesis.
Leaf of plant (a) has not synthesised starch as it does
not contain carbon dioxide which is essential for
photosynthesis. CO2
is absorbed by potassium
hydroxide. So, photosynthesis did not occur in
plant (a).

As given image in attachment:
Experimental set up (a) With potassium hydroxide
(b) Without potassium hydroxide.

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