Photosynthesis in Higher Plants
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ËÅRLÝ ËXPËRÏMËÑTS
1. ËXPËRÏMËÑTS BÝ JØSËPH PRÏËSTLËÝ (1770)
In 1770, Priestley performed
experiments to prove the
role of air in the growth of
green plants.
He discovered oxygen in 1774
during his experiment on
mint plant
He observed that a candle
burning in a closed bell jar
gets extinguished. Similarly, a
mouse soon suffocated in a
closed space. He concluded
that a burning candle or a
breathing animal damage
the air.
He placed a mint plant in
the same bell jar. He found that the mouse stayed alive and the candle
continued to burn.
He hypothesised that plants restore to the air whatever breathing
animals and burning candles had removed.
2. ËXPËRÏMËÑTS BÝ JÅÑ ÏÑGËÑHØÜSZ (1730 -1799)
He conducted the same experiment by placing
it once in the dark and once in the sunlight.
He showed that sunlight is essential to the
plant for purifying the air fouled by burning
candles or animals.
He repeated this experiment with an aquatic
plant. It showed that in bright sunlight, small
bubbles were formed around green parts while
in the dark they did not.
Later he identified these bubbles to be of oxygen.
Thus he showed that only the green parts of
plants release O2.
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