The Role of Chlorophyll During Photosynthesis

Plants provide energy for all the living organisms that feed on them, but plants do not start out having this energy. They have to produce it themselves in a process known as photosynthesis, the most essential element of which is chlorophyll, which has very distinct functions in the photosynthetic process.

Capturing Light

Most chlorophyll molecules work to absorb light energy. There are two types of chlorophyll. Each absorbs light at different wavelengths, creating a range from which energy can be absorbed that is greater than if each type were separately used by the plant cell. The result is that the chlorophyll is so effective at absorbing light that only wavelengths in the "green" area of the spectrum are reflected. This is why plants appear green.

Gas and Ion Production

The chlorophyll molecules transfer captured light energy to the reaction center of the cell, where electrons are exchanged, primarily with water molecules. This results in the production of oxygen gas and hydrogen ions.

Ion Movement and ATP

The hydrogen ions produced when the water molecules separate due to the chlorophyll molecules' charge have a positive charge. They therefore are attracted to molecules with a negative charge. The ions use the energy from the transfer of electrons in the cell to cross the thylakoid membrane. ATP, a nucleotide that transports energy within cells for metabolism, is produced from this movement.

Reduction of NADP+

ATP reduces a susbstance known as nicotinamide adenine dinucleotide phosphate (NADP+) into a simpler form called NADPH, which is used to reduce CO2, or carbon dioxide, into sugar. The plant then is able to store the sugar as food that it can use for growth and other processes.

Misconceptions and Comparisons

Chlorophyll often is described as changing light energy into glucose, but actions of chlorophyll molecules are really only the initial stages of the entire photosynthetic process. If photosynthesis is compared to the way a car works, then chlorophyll is a bit like the battery and starter mechanism. The chlorophyll molecules in the reaction center transfer are like the starter, putting the energy gathered by the other chlorophyll molecules (the battery) to work. The rest of the photosynthesis process is like the series of chemical reactions and mechanical movements that happen once the starter engages the engine. Additionally, when examining photosynthesis, the chlorophyll molecule tends to be connected more to the production of glucose than to the production of oxygen gas that people can breathe, even though this essential gas would not be released by the plant without the chlorophyll molecule.

References

• Chlorophyll (Paul May)