Photosynthesis

AP Biology· difficulty 3/5

Spinach leaf disks were vacuum-infiltrated with bicarbonate solution and illuminated. Their flotation rate is measured.

Why do the disks rise (float) over time?

A
$Photosynthesis produces O2 in the leaves, which makes them buoyant$
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B
$Light decreases water density$
C
$CO2 produced by the disks lifts them upward$
D
$Chlorophyll absorbs water, reducing disk density$

Explanation

O2 generated by the light reactions (from photolysis of H2O) accumulates in the leaf air spaces, increasing buoyancy.

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