What happens to a pigment molecule struck by light of energy higher than that of blue light?
AThe molecule is excited and holds the energy
BThe molecule reflects the light unchanged
CThe molecule passes the energy to water
DThe molecule is torn apart, which is bleaching
Answer & Solution
Correct answer: D. The molecule is torn apart, which is bleaching
1. Organic pigments have a narrow range of energy levels that they can absorb.
2. Energy levels lower than red light cannot raise an orbital electron to an excited state at all.
3. Energy levels higher than those in blue light physically tear the molecules apart.
4. That destruction is called bleaching.
5. This upper and lower limit together define the usable band of light.
6. An answer describing excitation applies only inside that band, not above it.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 8 "Photosynthesis", section 8.2 The Light-Dependent Reactions of Photosynthesis_
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