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.
Check out these related strategies to learn about the rest of photosynthesis and how it can inform additional plant-inspired technologies:
“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)
“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)