The figure shows the absorption spectrum for chlorophyll a and the action spectrum for photosynthesis. Why are they different?

• A. Green and yellow wavelengths of light inhibit the absorption of red and blue wavelengths.
• B. Oxygen given off during photosynthesis interferes with the absorption of light.
• C. Accessory pigments are absorbing light in addition to chlorophyll a which can be used in photosynthesis.
• D. Aerobic bacteria take up oxygen, which changes the measurement of the rate of photosynthesis.

Answer: (C)

Verified step by step guidance

1. Examine the absorption spectrum of chlorophyll a, which shows peaks at specific wavelengths where chlorophyll a absorbs light most effectively, typically in the blue (around 430 nm) and red (around 680 nm) regions.
2. Observe the action spectrum for photosynthesis, which indicates the overall rate of photosynthesis at different wavelengths of light. This spectrum often shows a broader range of effective wavelengths compared to the absorption spectrum of chlorophyll a alone.
3. Consider the role of accessory pigments, such as chlorophyll b, carotenoids, and xanthophylls, which absorb light at different wavelengths than chlorophyll a and transfer the energy to chlorophyll a, broadening the range of light that can drive photosynthesis.
4. Understand that the difference between the absorption spectrum of chlorophyll a and the action spectrum for photosynthesis is due to the presence of these accessory pigments, which enhance the efficiency of photosynthesis by capturing additional light energy.
5. Conclude that the correct explanation for the difference between the two spectra is that accessory pigments are absorbing light in addition to chlorophyll a, which can be used in photosynthesis, making option c the correct answer.