26. Low light intensities do not provide enough photons of
light for the light dependent reactions to make a large supply of ATP and NADPH.
This thus slows down the use of carbon dioxide during the light-independent
reactions.
At medium light intensities, increasing the light intensity
increases the rate of photosynthesis (more ATP and NADPH are made).
At high light intensity levels, water loss from the stomata
becomes a problem so they close. At this point carbon dioxide can't get into
the leaf so the rate of photosynthesis decreases as CO2 is a reactant for the
light-independent reactions.
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Long & Slichter