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What would be the reaction to show that glucose (C6H12O6) is being
synthesized? Write down a balanced equation to show this.
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(Refer the lessons Chemical equations, Carbon and its compounds in
your textbook of physical science class X).
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2 X Class Nutrition - Food supplying system
Van Neil first worked on purple sulphur bacteria and found light plays a specific
role in photosynthesis. Instead of H2O they used H2S as a starting material. Here no
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oxygen is liberated during photosynthesis instead, elemental sulphur is evolved. Later
he envisioned a similar process of photosynthesis in plants and proposed the above
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mentioned equation. Later Robert Hill showed that O2 is released from water during
this reaction. Then the equation was modified as follows.
Light
6CO2 + 12H2O C6H12O6 + 6H2O + 6O2
Chlorophyll
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NG
It is known that plants synthesize carbohydrates, the smaller simpler
ones first and from them, the more complex ones like starch and cellulose.
Plants are also capable of synthesizing all other compounds like proteins,
fats etc.
Animals are not capable of synthesizing carbohydrates and they have
to depend on plants for the same.
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Can we state that photosynthesis is the basic energy source for most
of the living world? Why, why not?
Let us study how the plants prepare carbohydrates through
photosynthesis.
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Activity-1
Presence of starch (a type of carbohydrate) in leaves
Let us take a leaf from a plant with soft and thin leaves and well exposed
to sun light.
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Arrange apparatus as shown in figure 2 (a). Take methylated spirit in a
test tube and put the leaf in it.
ER
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beaker
boiling water
leaf iodine solution
methylated spirit
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boiling tube
petridish
asbestos gauze
tripod stand
bunsen burner
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fig-2(a): boiling the leaf fig-2(b): Iodine test
in methylated spirit
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Free distribution by T.S. Government 2019-20 3
First boil the leaf in water then transfer this leaf into a test tube
containing methylated spirit. Boil this tube in a water bath. Chlorophyll
dissolves in spirit and the leaf becomes pale, due to removal of chlorophyll.
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Take the leaf carefully from test tube by using a brush.
Spread the leaf in a petridish and add a few drops of iodine/ betadine
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solution on it. Observe the leaf.