Page 9 - Science Class 07

through a split cork. Leave the plant in
sunlight for few hours. A er few hours
take out this leaf from conical flask and
remove it from the plant. Take another
leaf from the same plant. Test both these
leaves for presence of starch. You will
observe that the leaf from the conical
flask does not turn blue-black while the
one that was exposed to atmospheric air
turns blue-black. This shows that carbon
dioxide is necessary for photosynthesis.
Sunlight
No Carbon
dioxide
KOH
Carbon dioxide is necessary for photosynthesis. palm or thumb. If you take a lighted splinter
Reasons Why Photosynthesis is Important
v It is the number one source of oxygen in
the atmosphere.
v It contributes to the carbon cycle between
the earth, the oceans, plants and animals.
v It contributes to the symbio c rela onship
between plants, humans and animals.
v It directly or indirectly affects most life on
the earth.
v It serves as the primary energy process for
most trees and plants.
Aim : To check oxygen (O₂) is released
during the process of photosynthesis.
Material Required : A hydrilla plant, a
beaker, test tube, lighted splinter and a
water funnel.
Method : Take a beaker half filled with
water. Now, place the hydrilla plant at the
Science-7
centre of the beaker and cover in keeping
the funnel upside down. Place the test
tube full of water on the top of the funnel
inverted. Keep the beaker in the sunlight
for 2-3 hours.
Gas
Sunlight
Pond
Water
Support to
keep funnel Hydrilla
off the bo om
You will observe the gas bubbles appear in
the test tube and water level falls. This gas is
oxygen (O ) which is released by the hydrilla
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plant in the process of photosynthesis, now
take out the test tube closing its mouth with
near the mouth of the test-tube it starts
burning rapidly. It indicates the presence of
O in it.
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1. Is nutri on important for all living
beings?
2. Why are green plants called autotrophs?
3. Write chemical equa on for the process
of photosynthesis.
4. Why non-green plants cannot carry on
photosynthesis?
HETEROTROPHIC NURITION
Heterotrophic plants do not have the capacity
to produce enough food to sustain them.
Consequently, heterotrophic nutri on refers to
acquiring complex, already-made food. This
type of plant-food provides energy and
molecules and atoms that will help the plant to
repair or build new protoplasm. Heterotrophic
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