Question

Black paper
of photosynthesis. During light reaction, radiant energy of sun is trapped by chlorophyll and accessory pigments.
evolved during this reaction. Besides the production of O,, ATP and NADPH molecules are also produced during
1. Dark reaction takes place in stroma region of chloroplasts
. co, absorbed is reduced to form carbohydrates
phase. Food is stored in the form of starch. Starch gives blue colour with iodine solution.
RE:
Test negative for starch
a potted plant and place it in a darkroom for
days to destarch it.
se a suitable leaf, clean it and fix a strip of black
on both sides of this leaf as shown in the
ent figure. Use clips to hold the black paper.
place this potted plant in sunlight for 3 to
again.
the leaf which was partially covered by black
Test positive for starch
s leaf in water and then in alcohol to remove
orophyll.
he leaf with water and place it in iodine
Put the leaf in light for 6 hours
and then test for starch
Fig. 2: To illustrate that light is necessary for photosynthesis
serve the leaf.
NS : The covered part of the leaf remains yellow while the uncovered part turns blue black.
EXPLANATION : Blue-black colour of the leaf is due to presence of starch which is formed after photosynthe-
ant was kept in sunlight. Blue-black colour appears only in the light exposed part whereas covered part does
ve starch test. This shows that light is necessary for photosynthesis.
S:
ant must be destarched by placing it in dark for 3 to 4 days.
uld be decolourised before performing the starch test.
leaf in alcohol should not be directly done on flame. It should be done in water bath.
er should be properly fixed on the part of leaf.
VIVA-VOCE​

Answer 1

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