USA Biology Olympiad (USABO) Practice Exam

A red pigment extracted from a marine alga supports photosynthesis if it has which characteristic?

1. An absorption spectrum similar to the photosynthetic action spectrum

2. A high concentration of chlorophyll

3. Presence in terrestrial algae only

4. Detoxifying reactions with sunlight

The correct answer is: An absorption spectrum similar to the photosynthetic action spectrum

The correct answer highlights the relationship between a pigment's absorption spectrum and the photosynthetic action spectrum. For a pigment to support photosynthesis effectively, it must be able to absorb light at wavelengths that correspond to those used in the process of photosynthesis. The photosynthetic action spectrum depicts the wavelengths of light that are most effective in promoting photosynthesis, primarily in the blue (around 450 nm) and red (around 680 nm) regions of the electromagnetic spectrum. If the red pigment extracted from marine algae has an absorption spectrum that closely matches this action spectrum, it can effectively capture light energy needed for photosynthetic processes. While a high concentration of chlorophyll might enhance photosynthesis, it does not directly relate to the effectiveness of the red pigment in supporting the process. Furthermore, the presence of the pigment in terrestrial algae alone does not ensure its capability to support photosynthesis, as many functions and characteristics can differ between marine and terrestrial species. Lastly, detoxifying reactions with sunlight do not directly correlate with the pigment's ability to absorb light for photosynthesis. Thus, the key characteristic that enables the red pigment from marine algae to support photosynthesis is its absorption spectrum aligning with the conditions necessary for effective photosynthetic activity.