Question

Describe the relationship between an action spectrum and an absorption spectrum for photosynthesis, and explain why the absorption spectrum for chlorophyll differs from the action spectrum. I swear my teacher didn't teach us this.

Answer 1

The action and absorption spectrums show how much activity is going on at certain wavelengths. So you'd expect to see something like low amounts on the green area, since chlorophyll reflects green light away instead of absorbing it to make energy.
The action spectrum is just a graph of wavelength versus biological activity seen while absorption spectrum is the graph of wavelength versus absorption of energy.

Action spectrum is tested by putting a bunch of photosynthetic bacteria in a place full of a full spectrum of light and watching which wavelengths have the most bacteria moving around it and which ones are avoided, think of it like tastier wavelengths for the blue-green algae, so they clutter up and are counted.

Absorption just shoots different wavelengths at chlorophyll or other types of photosynthesizing matter and check how much of the energy is absorbed and how much is reflected off.

It should make sense how these will look similar, but are slightly different.