Question

An action spectrum plots the rate of photosynthesis at various wavelengths of visible light, and it shows that blue light with a wavelength of about 490 nm is effective in driving photosynthesis. Based on this information and the absorption spectra shown at left, what role may chlorophyll b and carotenoids play in photosynthesis?

-These pigments probably play only a photoprotective role (absorbing excess light energy that could damage chlorophyll a) and a role in producing the colors of fall foliage.
-Because chlorophyll a is found in the reaction-center complexes of both photosystems II and I, we can assume that these other pigments play no role in photosynthesis.
-These pigments are able to absorb more wavelengths of light (and thus more energy) than chlorophyll a alone can absorb. As part of light-harvesting complexes in photosystems, they broaden the range of light that can be used in the light reactions.

Answer 1

Chlorophyll b and carotenoids absorb wavelengths of light that chlorophyll a cannot, thus expanding the range of light that can be used for photosynthesis. They are part of the light-harvesting complexes, which transfer energy to chlorophyll a, driving the light reactions of photosynthesis.

Step-by-step explanation:

The role of chlorophyll b and carotenoids in photosynthesis extends beyond just protecting chlorophyll a (photoprotection) and contributing to fall foliage colors. They play a crucial role by absorbing wavelengths of light that chlorophyll a cannot, effectively broadening the absorption spectrum for photosynthesis. The absorption spectrum indicates the specific wavelengths of visible light that a pigment can absorb. Chlorophyll a mainly absorbs blue and red light, but it does not absorb green light, which is why plants appear green. However, chlorophyll b and carotenoids absorb different sets of wavelengths, such as blue and green light, including some that chlorophyll a cannot absorb.

The action spectrum of photosynthesis shows that blue light at about 490 nm is effectively used in the process, which is within the range of light absorbed by chlorophyll b and carotenoids. These pigments are components of the light-harvesting complexes within photosystems, where they capture light energy and transfer it to chlorophyll a at the reaction center, eventually driving the light reactions of photosynthesis. Therefore, these pigments are vital for maximizing the energy capture from sunlight and ensuring a wider range of light can be utilized for photosynthesis.