The chromatography paper is placed in the developing chamber with a solvent, which wicks up the paper, pulling the solvent up the paper by capillary action, and the mixture of pigments is dissolved as the solvent passes over it. The different components of the mixture move upward at different rates. A compound with greater solubility will travel farther than one with less solubility. The pigments then show up
as colour streaks on the chromatography paper. These substances have formed a pattern called a chromatogram on the chromatography paper.
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 and algae, pigments are the means by which the energy of sunlight is captured for the light dependent stage of 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 colour, to capture more of the sun's energy.
Chlorophylls are greenish pigments, which contain a porphyrin ring with magnesium at the centre. This is a stable ring-shaped molecule around which electrons are free to migrate. It is linked to a long hydrocarbon chain, and because the electrons move freely, the ring has the potential to gain or lose electrons easily, and thus the potential to provide energized electrons to other molecules. This is the fundamental process by which chlorophyll "captures" the energy of sunlight.
Chlorophyll absorbs two main colours from light quite well. These are blue and red. It reflects green light very well, however, the two different types of chlorophyll have their maximum absorption at different wavelengths of light.
Chlorophyll a, being the main photosynthetic pigment, has a primary purpose to convert light energy to chemical energy used by the plant itself. It passes its energized electrons on to molecules which will manufacture sugars for the plants growth.
The way in which chlorophyll a harnesses energy from sunlight is thus:
The light is thought of as photons, and each photon contains a certain amount of energy called a quantum. When a chlorophyll a molecule absorbs a photon, one of the pigments electrons is excited from its ground state. When in a chloroplast, the excited electron is passed onto a primary acceptor molecule (reduction). This is the first stage of the light dependent reactions.
All other photosynthetic pigments are known as accessory pigments, as they cannot transfer the suns energy directly to the photosynthetic pathway, instead they transfer the energy to chlorophyll a.
Chlorophyll b absorbs light in a region of the spectrum where chlorophyll a does not, and transfers the energy it produces to chlorophyll a. Along with chlorophyll b in transferring their energy produced to the chlorophyll a, two other pigments are found in plants. These are carotenes (orange) and xanthophylls (yellow), which can both come under the heading “carotenoids”. Since chlorophyll is such a dominant pigment in green plants, this domination hides the colour of the carotenes and xanthophylls in the leaves. This causes most plant leaves to appear green most of the time. During the autumn, however, the chlorophyll starts to break down, causing the carotenes and xanthophylls to show their bright red, orange and yellow colours.
Xanthophylls are yellowish pigments which include the compound carotene, which gives carrots their colour. They 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. They transfer all their energy to chlorophyll a.
