Photosynthetic Pigments Essay

The Importance of Photosynthetic Pigments in Nature

Photosynthetic pigments are essential for life because they allow photosynthesis to occur by capturing sunlight which is then used alongside carbon dioxide and water to form organic compounds such as glucose and oxygen. The pigments allow the conversion of light energy to chemical energy which other organisms can benefit from. Oxygen is utilised by other organisms in aerobic respiration. The different pigments present in the chloroplasts allow a wide variety of wavelengths of light to be absorbed for efficient photosynthesis and provide colours to the plant to attract pollinators.

The photosynthetic pigments are important because they donate the electrons needed to start the sequence of reactions

The structure of chlorophyll involves a hydrophobic tail embedded in the thylakoid membrane which repels water and a porphyrin ring which is a ring of four pyrrols (C4H5N) surrounding a metal ion which absorbs the incoming light energy, in the case of chlorophyll the metal ion is magnesium (Mg2+.) The electrons within the porphyrin ring are delocalised so the molecule has the potential to easily and quickly lose and gain electrons making the structure of chlorophyll ideal for photosynthesis. Chlorophyll is the most abundant photosynthetic pigment, absorbing red and blue wavelengths and reflecting green wavelengths, meaning plants containing chlorophyll appear green. There are many types of chlorophyll, including chlorophyll a, b, c1, c2, d and f. Chlorophyll a is present in all photosynthetic organisms and is the most common pigment with the molecular formula C55H72MgN4O5. Chlorophyll b is found in plants with the molecular formula C55H70MgN4O6, it is less abundant than chlorophyll a. Chlorophyll a and b are often found together as they increase the wavelengths of light absorbed. Chlorophyll c1 (C35H30O5N4Mg) and c2 (C35H28O5N4Mg) are found in algae, they are accessory pigments and have a brown colour. Chlorophyll c is able to absorb yellow and green light (500-600nm) that chlorophyll a

They are accessory pigment molecules that cascade light energy to primary pigments. Carotenoids absorb wavelengths in the blue and green region of the visible spectrum (400-550nm) and reflect wavelengths of 590-650nm so appear red-orange in colour. They are found in all plants and some photosynthetic bacteria. Carotenoids are separated into two groups, carotenes and xanthophylls. Carotenes (C40H56) are polyunsaturated hydrocarbons containing no oxygen and include pigments such as α-carotene, β-carotene, and lycopene. They give the orange colour to carrots and autumn leaves. Xanthophylls (C40H56O2) contain oxygen and include lutein and zeaxanthin. Carotenoids contain alternating carbon-carbon double bonds and single bonds, forming a conjugation system where electrons in the fourth outer shell are in p-orbitals which overlap. This overlapping produces a system of π-bonds with delocalised electrons. The delocalised electrons are free to move so are more easily lost because less energy is needed to raise them to an excited state. Shorter wavelengths towards the blue end of the spectrum with lower energies are absorbed because of the lower energy