Photosynthetic Pigments

Photosynthetic Pigments

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The term "pigment" means colored substance. The color of the photosynthesizing pigment depends on the ranges of the visible light spectrum that it absorbs or reflects.

Chlorophyll, which gives the green color characteristic of most vegetables, absorbs light very well in the red and violet bands, reflecting green light.

Because reflected light is the light that hits our eyes, this is the color we see as we look at a leaf. The light absorption profile of a substance is its absorption spectrum.
All photosynthesis cells except bacterial cells contain 2 types of chlorophyll, and one of them is always the chlorophyll a. The second type of chlorophyll is usually the chlorophyll b (in the higher vegetables) or the chlorophyll c (in many algae). These various types of chlorophyll differ in the range of the visible light spectrum in which each of them captures light most efficiently.

Chlorophylls The and B have slightly different light absorption spectra as shown in the following graph:

We can verify by analyzing the graph that both chlorophylls have two absorption peaks: one higher in the violet range and one smaller in the red range.

Carotenoids are accessory pigments. They absorb light in slightly different ranges from chlorophyll bands. The presence of these accessory pigments makes many leaves have different colors than green. Although they have chlorophyll, the presence of these other pigments in large quantities masks their presence and leaves the leaves with other colors (purplish, orange, yellow, etc.).

Many leaves change color in winter by decreasing the amount of chlorophyll. As the amount of other pigments does not change so significantly, their colors are seen, making the leaves generally yellow.

The role of light in photosynthesis

The atomic structure of certain substances is such that they are capable of absorbing light. When light strikes an atom capable of absorbing it, some electrons are activated and raised to a higher energy level. The atom enters a "state enabled", rich in energy and very unstable. When the excited electrons return to their normal orbitals, the atom returns to its base state. This return is accompanied by the release of energy as heat or as light. The light emitted in this way is called fluorescence.

In chloroplasts, chlorophyll molecules have this characteristic. However, its excited electron does not return the energy captured by fluorescence, but transfers it to other substances. There is therefore transformation of the captured light energy into chemical energy.