Page 7 - Science Class 07
P. 7
The hydrogen from the water molecules
sunlight so this part of the leaf could not
combines with carbon dioxide (CO ) from the
2 carry out the process of photosynthesis.
environment to form glucose, a simple sugar.
Now, we can say that sunlight is necessary for
Plant takes in CO through small pores present
2 the process of photosynthesis.
in their leaves called stomata.
Photosynthesis is the only process on the
earth by which solar energy is trapped by
green plants and converted into the food for
the rest of the organisms. About 170 million
Stomata of Leaf tonnes of dry ma er is produced by this
The glucose molecules are held together by the process annually. Plants u lise only 0.2% of
chemical energy. In other words, the energy is the solar energy and produce food to meet
trapped within the glucose molecules. the food requirement for all the other
We can represent the overall process of organisms.
photosynthesis through the following equa on.
chlorophyll
Carbon dioxide + Water Glucose + Oxygen
sunlight Aim : To check chlorophyll is necessary for
the process of photosynthesis.
Materials required : A po ed plant of croton,
Aim : To check plant can carry out the paper, pencil, alcohol and iodine solu on.
process of photosynthesis without sunlight. Method : The leaves of a croton plant
Materials Required : A po ed plant, a contain chlorophyll at certain por on. The
cellophane tape, black strips, cardboard and rest parts are non-green because in these
iodine solu on. parts chlorophyll is absent. Place the plant in
the dark for 2-3 days to destarch it. Now,
Method : Keep the plant in dark for 2-3 days
to destarch it. Now, cover a por on of both keep the plant in sunlight for 2-3 hours.
the sides, of a leaf with black strips. Fix the Now, draw an outline of a leaf on a paper
strips with the help of cellophane tape. Now, and indicate its green and non-green part on
keep the plant in the sunlight for 5-6 hours. the paper.
Pluck the leaf and remove the strips. To test Now, perform iodine test and compare the
the leaf for starch, put a few drops of iodine stained parts with the drawing.
solu on on the leaf. You will observe that the green areas have
You will observe that the leaf turns blue turned blue black while the non-green areas
black all over except the por on covered have turned brown. This shows that only
with black strips, the por on become brown. green area which contains chlorophyll can
The covered por on remained deprived of manufacture starch.
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