Understanding Photosynthetic Pigment Chemical Formulae

Photosynthetic pigments are molecules found in plants, algae, and bacteria that absorb light energy for photosynthesis. Different pigments absorb light at different wavelengths. Some of the primary pigments include chlorophylls, carotenoids, and xanthophylls. Each pigment has a specific chemical structure and formula.

Analyzing the Chemical Formulae of Photosynthetic Pigments

Let's examine the common chemical formulae for the pigments mentioned in the statements:

• Chlorophyll a: This is the primary photosynthetic pigment and has the chemical formula \(\text{C}_{55}\text{H}_{72}\text{O}_5\text{N}_4\text{Mg}\).
• Chlorophyll b: An accessory pigment, chlorophyll b, has a slightly different formula compared to chlorophyll a, which is \(\text{C}_{55}\text{H}_{70}\text{O}_6\text{N}_4\text{Mg}\). Note the difference in hydrogen and oxygen atoms.
• Carotenoids: These are a group of accessory pigments. They are typically hydrocarbons (composed only of carbon and hydrogen). A common example is \(\beta\)-carotene, with the formula \(\text{C}_{40}\text{H}_{56}\).
• Xanthophylls: These are oxygenated carotenoids, meaning they have oxygen atoms in addition to carbon and hydrogen. A common example is Lutein, with the formula \(\text{C}_{40}\text{H}_{56}\text{O}_2\).

Evaluating Each Statement

Now let's compare the provided statements with the correct chemical formulae:

• Statement (1) Carotenoid - \(\text{C}_{55}\text{H}_{70}\text{O}_6\text{N}_4\text{Mg}\): This statement gives a formula that includes Oxygen, Nitrogen, and Magnesium. Carotenoids, like \(\beta\)-carotene (\(\text{C}_{40}\text{H}_{56}\)), are hydrocarbons or oxygenated hydrocarbons (xanthophylls) and do not contain Nitrogen or Magnesium. The given formula is actually that of Chlorophyll b. Therefore, statement (1) is incorrect.
• Statement (2) Chlorophyll 'a' - \(\text{C}_{55}\text{H}_{72}\text{O}_5\text{N}_4\text{Mg}\): This formula correctly matches the known chemical formula for Chlorophyll 'a'. Therefore, statement (2) is correct.
• Statement (3) Chlorophyll 'b' - \(\text{C}_{55}\text{H}_{70}\text{O}_6\text{N}_4\text{Mg}\): This formula correctly matches the known chemical formula for Chlorophyll 'b'. Therefore, statement (3) is correct.
• Statement (4) Xanthophyll - \(\text{C}_{50}\text{H}_{70}\text{O}_5\text{Mg}\): This statement provides a formula containing Magnesium, which is not present in xanthophylls. Typical xanthophylls, like Lutein (\(\text{C}_{40}\text{H}_{56}\text{O}_2\)), have a different structure and composition. Therefore, statement (4) is incorrect.

Identifying the Correct Matches

Based on our analysis:

• Statement (1) is incorrect.
• Statement (2) is correct.
• Statement (3) is correct.
• Statement (4) is incorrect.

The statements that are correct are (2) and (3).

Conclusion

The option that lists (2) and (3) as correct statements is the right answer.

Revision Table: Photosynthetic Pigment Formulae

Additional Information on Photosynthetic Pigments

Photosynthetic pigments play a vital role in capturing light energy. They are located in the chloroplasts of plant cells, specifically within the thylakoid membranes.

• Chlorophylls: These are the most abundant pigments and absorb strongly in the blue and red parts of the spectrum, reflecting green light (hence plants appear green). Their structure includes a porphyrin ring with a magnesium ion at the center and a long phytol tail. Chlorophyll a is found in all photosynthetic eukaryotes and cyanobacteria, while chlorophyll b is found in plants, green algae, and euglenoids.
• Carotenoids: These pigments absorb light mainly in the blue-green region of the spectrum. They serve several functions, including transferring absorbed energy to chlorophyll, protecting chlorophyll from photodamage (acting as antioxidants), and contributing to the yellow, orange, or red colors in fruits, flowers, and autumn leaves. Carotenoids are generally made of isoprene units and can be linear or cyclic. They are divided into two main groups: carotenes (hydrocarbons) and xanthophylls (oxygen-containing derivatives of carotenes).
• Absorption Spectra: Different pigments have different absorption spectra, meaning they absorb light most effectively at different wavelengths. This broadens the range of light energy that can be harvested for photosynthesis. For example, carotenoids can absorb light that chlorophylls do not, and this energy is then transferred to chlorophyll a for use in photosynthesis.