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Pigment molecules absorb and transfer solar energy: Cooke’s koki’o

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Kokia cookei (Cooke's koki'o) / Tina Fuller / LicenseCC-by - Attribution

Pigment molecules in plants absorb and transfer solar energy using a special arrangement that funnels light toward a reaction center

FUNCTION
Summary
The process of photosynthesis in plants involves a series of steps and reactions that use solar energy, water, and carbon dioxide to produce organic compounds. One of the first steps in this complex process depends on chlorophyll and other pigment molecules.

Chlorophyll is the green pigment molecule that makes plants appear green. In photosynthetic plant cells, chlorophyll molecules are embedded in stacked membranes (thylakoids) contained in special membrane-bound organelles called chloroplasts. The chlorophyll molecules are arranged in discrete units called photosystems, each of which contains hundreds of pigment molecules (chlorophyll plus others) arranged into an “antenna complex” surrounding a reaction center. 

When light hits a pigment molecule in the antenna complex, the light energy “excites” the molecule, causing its electrons to jump to a higher level of energy. This excited state is temporary, and when the electrons fall back to a lower energy level, energy is released. This released energy can be transferred to a neighboring pigment molecule and so on, creating a chain of excited pigment molecules that ultimately deliver the energy to the photosystem’s reaction center. The reaction center contains special chlorophyll molecules that have a specific response to absorbing energy: rather than transferring only energy, the chlorophyll’s resulting high-energy electrons are transferred themselves to an electron-acceptor molecule, which begins the flow of electrons that plays a key role in the rest of photosynthesis.

Dye-sensitized solar cells are an example of a plant-inspired technology, where light sensitive dye molecules (commonly containing the metal ruthenium, but organic dyes are being developed, as well) are used to absorb and transfer solar energy. Dye-sensitized solar cells are alternatives to more expensive silicon-based solar cells.
Excerpt
“There are several kinds of chlorophyll, which differ from one another both in the details of their molecular structure and in their specific absorption properties. Chlorophyll a occurs in all photosynthetic eukaryotes and in the cyanobacteria. Not surprisingly, chlorophyll a is essential for the oxygen-generating photosynthesis carried out by organisms in these groups.” (Raven et al. 1999:133)

“All of the pigments within a photosystem are capable of absorbing photons, but only one pair of special chlorophyll a molecules per photosystem can actually use the energy in the photochemical reaction. This special pair of chlorophyll a molecules is situated at the core of the reaction center of the photosystem. The other pigment molecules, called antenna pigments because they are part of the light-gathering network, are located in the antenna complex. In addition to chlorophyll, varying amounts of carotenoid pigments are also located in each antenna complex.” (Raven et al. 1999:135)

“The primary processes in all photosynthetic systems involve the absorption of energy from (sun) light by chromophores in a light harvesting antenna, and the subsequent transfer of this energy to a reaction centre (RC) site where the energy is ‘trapped’ by means of a stable charge separation.


Photosystem (PS) I is one of two such photosystems in oxygenic photosynthesis. When co-operating with PS II it uses the energy of light to transfer electrons from plastocyanin or soluble cytochrome c6 to ferredoxin and eventually to NADP+. In an alternative pathway, the electrons from ferredoxin are transferred back to plastocyanin via the cytochrome b6f complex. This cyclic electron transport, which does not require the input of free energy by PS II, results in a transmembrane electrochemical gradient that can be used to produce ATP.

In plants and green algae the PS I complex consists of two separable functional units: the PS I core, and the light harvesting complex (LHC) I peripheral antenna. The PS I complex in cyanobacteria does not possess the peripheral LHCI antenna, but since the PS I core complexes of cyanobacteria bear a large resemblance to the core complex of plants, a direct comparison of the energy transfer and trapping properties of these complexes is justified.” (Gobets and Grondelle 2001:80)
About the inspiring organism
Med_52459 Cooke's koki'o
Kokia cookei O. Deg.
Common name: Moloka‘i koki‘o

Habitat(s): Forest
Learn more at EOL.org
Some organism data provided by: ITIS: The Integrated Taxonomic Information System
Organism/taxonomy data provided by:
Species 2000 & ITIS Catalogue of Life: 2008 Annual Checklist

Threat Categories LONG_EW IUCN Red List Status: Extinct in the Wild

Bioinspired products and application ideas

Application Ideas: Dye-sensitized solar cells. Photo-sensitive dyes. Energy transfer.

Industrial Sector(s) interested in this strategy: Energy development, Chemistry



References
Gobets B; van Grondelle R. 2001. Energy transfer and trapping in photosystem I. Biochimica et Biophysica Acta. 1507: 80-99.
Learn More at Google Scholar Google Scholar  

O’Regan B; Grätzel M. 1991. A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature. 353: 737-740.
Learn More at Google Scholar Google Scholar  

Raven PH; Evert RF; Eichhorn SE. 1999. Biology of plants. New York: W.H. Freeman and Company. 944 p.
Learn More at Google Scholar Google Scholar  

Comments

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Daro1003
over 3 years ago
This comment was removed by a AskNature editor for the following reason:
SPAM
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Sherry
over 4 years ago
Cooke's koki'o is just an example of a plant for the purposes of talking about photosynthesis. In general in AskNature we show the species that was actually studied, but for more general strategies like photosynthesis, we sometimes picked an endangered species to illustrate how much we lose when we lose a species from Earth.
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MaryBall
over 4 years ago
How could a Hawaiian tree that is extinct in the wild (see the recovery plan at http://ecos.fws.gov/docs/recovery_plan/980527.pdf) possibly have been the inspiration for a dye-based solar cell??
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stgula20
over 6 years ago
This comment was removed by a AskNature editor for the following reason:
It was a test message.
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stgula20
over 6 years ago
This comment was removed by a AskNature editor for the following reason:
It was a test message.
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admin
over 7 years ago
A couple related news stories:

Harnessing Light:
http://pubs.acs.org/cen/science/87/8715sci1.html

Attempts To Mimic A Plant's Light-Harvesting And Water-Splitting Megamachinery:
http://pubs.acs.org/cen/science/87/8715sci1a.html
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