Importance of Light in Photosynthesis

Photosynthesis cannot occur without light.

Photosynthesis is a compound word formed from the prefix photo for light and the suffix synthesis for putting things together. As its name would imply, photosynthesis is a process that requires light.

Identification

The energy of a photon of light is given by the equation E = hv, where E is energy, h is Planck's constant and v is the frequency. Electrons can only absorb photons that have energies equivalent to the difference in energy level between the atomic or molecular orbital the electron occupies and another of the orbitals available to it. Plant cells contain pigments that preferentially absorb light from different regions of the spectrum. Sunlight is the energy source that powers photosynthesis--rather like the fuel that powers your car.

Types

Photosynthesis is divided into two stages or series of reactions. The first stage and the one that involves light is called the light reactions. The light reactions capture solar energy for use in the second stage, the light-independent reactions, which fix carbon from the atmosphere in the form of carbon dioxide.

Function

A photon of light striking a molecule of chlorophyll is absorbed by an electron; this energy is transferred to another molecule of chlorophyll and then to another molecule in turn through a complex of pigment molecules called the antenna complex. Eventually the energy is transferred to a special pair of pigment molecules called the P680 complex, which pass an excited electron off to another molecule called the primary acceptor. The electron lost by P680 is replaced by an electron from a water molecule, while the excited electron from the primary acceptor is transferred to a series of proteins called the electron transport chain. These proteins will use the energy to drive the synthesis of two molecules, ATP and NADPH, which will in turn fuel the light-independent reactions.

References

• Real Trees 4 Kids: Photosynthesis
• "Biology"; Neil A. Campbell, Jane B. Reece, Lisa A. Urry, Michael L. Cain, Peter V. Minorsky, Steven A. Wasserman, Robert B. Jackson; 2008