Do plants absorb energy from the entire solar spectrum? If not then how do plants filter out the energy wavelengths to be used from solar spectrum?

75 Terrawatts of energy is used daily by the plants for photosynthesis. Even though this is a big number its just .1% of total energy received from the sun daily,166 petawatts. But still this is more than 4 times the annual consumption of energy by humans, 16 terrawatts.

Plants mostly absorb from red and blue portions of the solar spectrum (cyanobacteria can photosynthesize from IR)

Antenna complex within the leaves of the plant are responsible for extracting energy from the sunlight. These molecular nanoantennas work on the principle of resonance energy transfer. In simple terms each section of antenna extracts energy from a particular wavelength of light and pass on the rest. Other sections of antenna the extract energy from the portion of light they accept and pass on the rest.

Although these molecules are called "antenna complex" they are actually organic semiconductors.

They absorb only those frequencies of light that fall within their band gap. The proof can be found in their fluorescence spectrum. Excitation by higher energy wavelengths of light leads to electronic excitation,charge separation,recombination and finally emission of visible light. It is this visible light emission indicates a band gap which falls in the range that is typical of semiconductors.

The antenna complex molecules obey the principle of optoelectronic reciprocity and fluoresce in the red and blue portions when excited by UV light.

The term antenna refers to how the energy is transferred between distributed molecules within the leaf each set of which absorbs from different wavelengths of light. Because sun is a continuous broadband source of emission no single uniform material (like silicon) can absorb from the entire spectrum. At best they can only absorb a tiny subset of energy (like red in silicon). To create a broadband absorber a conjunction of diffrent materials is needed. Nature understood this long ago and has successfully managed to design systems overcome this limitation. Antenna complex provide a ready made biological template that can serve as an inspiration for the design of such complex systems in future.

Understanding the properties of antenna complex within the leaves can help us design better organic semiconductors for use in computing,lighting and energy applications. The following paper analyzes the physical properties -- electronic structure ,band gap , optical properties,geometry of the antenna complex molecules and describes how light is absorbed ,energy is transferred and charge is separated in the photosynthetic molecules with >90% quantum efficiency.

Light Absorption and Energy Transfer in the Antenna Complexes of Photosynthetic Organisms https://www.life.illinois.edu/govindjee/recent_papers_files/2016ReviewChemRev.pdf

#organic #semiconductors #biophysics

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