Question

The action spectrum of photosynthesis shows a high light absorption for violet/blue and orange/red and a low absorption for green/yellow. If we were to set up an experiment where narrow bands of unicolored light were shown on an aquatic plant such as Elodea, and we counted the number of bubbles of oxygen produced as an indicator of photosynthetic rate, how would the graph appear?

A. just like the action spectrum with peaks at violet/blue and orange/red and a trough at yellow/green
B. exactly inverted from the action spectrum with a peak for yellow/green
C. perfectly flat because many wavelengths are used by chlorophyll
D. a descending line because ultra-violet has more energy than infra-red
E. There is no way to guess without actually running the experiment.

Answer 1

The graph from the experiment would show peaks at violet/blue and orange/red, and a trough at green/yellow, matching the action spectrum of photosynthesis (option A).

Step-by-step explanation:

If an experiment were to measure the photosynthetic rate of an aquatic plant like Elodea by counting the number of oxygen bubbles produced under different colors of light, the resulting graph would correspond to the action spectrum of photosynthesis. Given that the action spectrum reflects the efficacy of different wavelengths of light in driving photosynthesis, and considering that pigment molecules absorb only specific wavelengths, there would be peaks at violet/blue and orange/red where chlorophylls and accessory pigments like carotenoids absorb light most effectively. Conversely, there would be a trough in the green/yellow region where these pigments absorb less light, as this light is reflected, making chlorophyll appear green.