194 |
A Handbook of Biology
PHØTØSÝÑTHËSÏS
Photosynthesis is a
physico-chemical
process by which
green plants use light
energy (solar energy)
to synthesise organic
compounds.
Photosynthesis is the
basis of life on earth.
Ultimately, all living forms
depend on sunlight for
energy.
Chlorophyll (green pigment of the leaf), light, water and CO2
are required for the photosynthesis to occur.
ÏMPØRTÅÑÇË ØF PHØTØSÝÑTHËSÏS
01
It is the primary source of all food on earth.
02
It releases oxygen into the atmosphere
ËXPËRÏMËÑTS RËLÅTËD WÏTH PHØTØSÝÑTHËSÏS
1. VÅRÏËGÅTËD LËÅF ËXPËRÏMËÑT
Take a variegated leaf (or leaf partially covered with black paper) that
was exposed to light.
Test the leaves for starch. It shows that photosynthesis occurs only in
green parts of the leaves in presence of light.
2. HÅLF-LËÅF ËXPËRÏMËÑT
A part of a leaf is enclosed in a test tube containing KOH soaked cotton
(which absorbs CO2).
The other half of the leaf is exposed to air.
Place this setup in light for some time.
Test the leaf for presence of starch. Exposed part tests positive for starch
and portion in the tube tests negative. This proves that CO2 is required
for photosynthesis.