What plant pigments are involved in photosynthesis

Pigments are colorful compounds.

Pigments are chemical compounds which reflect only certain wavelengths of visible light. This makes them appear "colorful". Flowers, corals, and even animal skin contain pigments which give them their colors. More important than their reflection of light is the ability of pigments to absorb certain wavelengths.

Because they interact with light to absorb only certain wavelengths, pigments are useful to plants and other autotrophs --organisms which make their own food using photosynthesis. In plants, algae, and cyanobacteria, pigments are the means by which the energy of sunlight is captured for photosynthesis. However, since each pigment reacts with only a narrow range of the spectrum, there is usually a need to produce several kinds of pigments, each of a different color, to capture more of the sun's energy.

There are three basic classes of pigments.

Carotenoids are usually red, orange, or yellow pigments, and include the familiar compound carotene, which gives carrots their color. These compounds are composed of two small six-carbon rings connected by a "chain" of carbon atoms. As a result, they do not dissolve in water, and must be attached to membranes within the cell. Carotenoids cannot transfer sunlight energy directly to the photosynthetic pathway, but must pass their absorbed energy to chlorophyll. For this reason, they are called accessory pigments. One very visible accessory pigment is fucoxanthin the brown pigment which colors kelps and other brown algae as well as the diatoms.

Phycobilins are water-soluble pigments, and are therefore found in the cytoplasm, or in the stroma of the chloroplast. They occur only in Cyanobacteria and Rhodophyta.

The picture at the right shows the two classes of phycobilins which may be extracted from these "algae". The vial on the left contains the bluish pigment phycocyanin, which gives the Cyanobacteria their name. The vial on the right contains the reddish pigment phycoerythrin, which gives the red algae their common name.

Phycobilins are not only useful to the organisms which use them for soaking up light energy; they have also found use as research tools. Both pycocyanin and phycoerythrin fluoresce at a particular wavelength. That is, when they are exposed to strong light, they absorb the light energy, and release it by emitting light of a very narrow range of wavelengths. The light produced by this fluorescence is so distinctive and reliable, that phycobilins may be used as chemical "tags". The pigments are chemically bonded to antibodies, which are then put into a solution of cells. When the solution is sprayed as a stream of fine droplets past a laser and computer sensor, a machine can identify whether the cells in the droplets have been "tagged" by the antibodies. This has found extensive use in cancer research, for "tagging" tumor cells.

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A pigment is a generic term for a molecule that absorbs light and has a color. Plants contain many pigments, giving rise to the various colors we see. Flowers and fruits obviously contain a large number of organic molecules that absorb light. Leaves, stems and roots also contain a variety of pigments. Such pigment molecules include anthocyanins, flavanoids, flavines, quinones and cytochromes, just to name a few. However, none of these should be considered a photosynthetic pigment. Photosynthetic pigments are the only pigments that have the ability to absorb energy from sunlight and make it available to the photosynthetic apparatus. In land plants, there are two classes of these photosynthetic pigments, the chlorophylls and the carotenoids.

The ability of chlorophyll and carotenoid molecules to absorb the energy of light and use it effectively is related to their molecular structure and to their organization within the cell. You learned in a previous lesson (The Interaction of Light with Biological Molecules) that pigments absorb the energy from photons through systems of conjugated double bonds. Examine the molecular structure of representative chlorophyll and carotenoid molecules in Figures: Structure A and B.

Structure A: Molecular structure of lutein, a carotenoid.

Notice the linear system of conjugated double bonds in the carotenoid (lutein) and the zig-zag of conjugated double bonds in the large ring structure of the chlorophyll. These systems of conjugated double bonds are responsible for the ability to absorb light energy from photons.

Structure B: Molecular structure of chlorophyll.

What are the 4 types of plant pigments?

What are the 3 pigments found in plants?

How many pigments are involved in photosynthesis?