Page 110 - ICSE Chemistry 6

in nature. One such process which runs on a large scale in nature
to maintain a balance between the levels of oxygen and carbon
dioxide is photosynthesis. sun
O released
Photosynthesis is a process by which plants make their food using 2
carbon dioxide, sunlight and water. Photosynthesis is carried
CO 2
out only by green plants because they contain a green-coloured
pigment called chlorophyll. The following equa on explains the leaves contain
chlorophyll
process clearly.
CO 2 sugar is formed
Sunlight + Water + Carbon dioxide Chlorophyll Food + Oxygen (food)

Photosynthesis occurs only during the day me as sunlight is essen al
for the process. The oxygen produced during photosynthesis is root absorbs
water
many mes the quan ty used by plants during respira on.
Therefore, respira on and photosynthesis are two opposing Fig. 5.3: Photosynthesis
processes. In respira on, oxygen is needed to break down the food,
and carbon dioxide and water are produced. In
photosynthesis, carbon dioxide and water are photosynthesis
O
2
needed to make food and oxygen is produced as
a by-product.

This way, the composi on of gases is fairly
maintained in the atmosphere. However,
thoughtless human ac vi es such as large scale
deforesta on and excessive burning of fossil plant
fuels are disturbing this balance considerably. If
this happens to con nue then we will have to CO 2
respiration animal
face dras c results in the future. So, we should
plant more trees and reduce pollu on in every Fig. 5.4: Balance of oxygen and carbon dioxide in nature
possible manner.

Activity 5.9

Aim: To show that green plants produce oxygen during photosynthesis

Materials required: A trough, some water, few cu ngs of Hydrilla, a funnel, a test tube, a glowing splinter
Procedure

• Fill a trough (about three-fourths) with water.
• Place a few cu ngs of Hydrilla (a water plant) in it and cover them
with a funnel as shown in the fi gure.
• Fill a test tube with water and cover its mouth with your thumb.

• Place it over the stem of the funnel.
• Keep the set-up in sunlight for a few hours.

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