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Photosynthesis in Higher Plants
Emerson Effect and Red Drop
1 question from 1 paper, each with its answer.
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- paper
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Concepts tested
- PS II not excited beyond 680 nm
All Questions
2001 AIPMT 1 question
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Which pigment system is inactivated in red drop : -Emerson observed that the quantum yield of photosynthesis falls sharply when the wavelength of light is above 680 nm, even though chlorophyll still absorbs it. This is called the red drop.
Light of wavelength above 680 nm can excite PS I (P700) but not PS II (P680).
Since both photosystems are needed for non-cyclic photophosphorylation and splitting of water, photosynthesis falls when PS II is not working.
When far-red light is supplemented with shorter-wavelength red light, the rate increases more than the sum (Emerson enhancement effect).
So PS II is inactivated in the red drop.