Question

Photosynthetic pigments such as chl \(a\), chl \(b\), xanthophyll and carotene can be separated by which of the following techniques? (a) Paper chromatography (b) Gel Electrophoresis (c) \(X\)-ray diffusion (d) ELISA test

Short answer

Photosynthetic pigments like chlorophylls and carotenoids can be separated by paper chromatography.

Step-by-step solution

Understanding the principle of separation

First, recognize that different techniques separate molecules based on different properties. Paper chromatography separates compounds based on their solubility and affinity to the paper and solvent, gel electrophoresis separates based on size and charge, X-ray diffraction is used for determining the atomic structure of crystals, and ELISA is an assay to detect and quantify substances such as proteins, peptides, antibodies, and hormones.

Identifying the unique properties of photosynthetic pigments

Photosynthetic pigments, including chlorophylls and carotenoids, are colored molecules that are soluble in organic solvents. They differ from each other in their solubility and affinity towards the stationary (paper) and mobile (solvent) phases during chromatography.

Selecting the appropriate technique

Since photosynthetic pigments have distinct solubility and affinity properties and need to be separated based on these differences, paper chromatography would be the appropriate technique for separating these pigments.

Eliminating incorrect options

Gel electrophoresis is mainly used for nucleic acids and proteins, X-ray diffraction for crystalline structures, and the ELISA test for specific molecules in immunoassays, which are not suitable for separating photosynthetic pigments.

Key concepts

Paper Chromatography

Paper chromatography is a method widely used in chemistry to separate and identify substances that are or can be made to be colored, especially pigments. This technique exploits the differences in polarity between compounds.

Here's the basic principle behind paper chromatography: a sample is applied to a piece of chromatography or filter paper, known as the stationary phase. Then, the paper is placed in a container with a shallow level of solvent, or mobile phase. As the solvent soaks up through the paper by capillary action, it carries along with it the compounds in the sample that were applied to the paper. The key factor is that different compounds will move with the solvent at different rates.

• Compounds that are more soluble in the solvent will travel further up the paper.
• Compounds that bond strongly to the paper will not travel as far.

This creates a series of spots separated along the paper strip. Each spot corresponds to a different compound in the original mixture, and the position of the spot provides information about the compound's polarity and solubility.

When separating photosynthetic pigments, like chlorophyll and carotenoids, each of these pigments has a different affinity to the mobile and stationary phases, resulting in distinct bands on the chromatography paper following the separation.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in molecules of glucose. This transformation is one of the fundamental processes of life as it is the primary source of organic molecules for nearly all other organisms.

For photosynthesis to occur, organisms use pigments to capture the energy from sunlight. Chlorophyll, the main pigment in plants, absorbs mainly blue and red light and reflects green, which is why plants appear green to our eyes. Other pigments, like carotenoids, absorb different wavelengths of light and provide additional energy absorption capacity, as well as photoprotection for the plant.

• Photosynthesis occurs in two main stages: light-dependent reactions and the Calvin cycle.
• The light-dependent reactions convert light energy into chemical energy in the form of ATP and NADPH.
• The Calvin cycle uses ATP and NADPH to convert CO2 into glucose.

The role of pigments in capturing light makes them crucial to the efficiency of photosynthesis and, by extension, the life-sustaining energy cycle on Earth.

Chlorophyll

Chlorophyll is a family of green pigments found in all photosynthetic organisms, including plants, algae, and cyanobacteria. It serves as the primary driver of photosynthesis by enabling the capture of sunlight, allowing plants to convert carbon dioxide and water into glucose and oxygen.

There are different types of chlorophyll, with chlorophyll a being the most abundant and most essential for the photosynthetic process.

• Chlorophyll a is the primary pigment that initiates the transformation of light into chemical energy.
• Chlorophyll b serves as an accessory pigment, broadening the range of light a plant can use for energy.

Both chlorophyll a and chlorophyll b absorb light most effectively in the blue and red wavelengths, but their solubility and affinity for the paper and solvent in paper chromatography differ, leading to their separation. Importantly, chlorophyll's role is not just in photosynthesis; its presence also influences a plant's growth and health.

Carotenoids

Carotenoids are a class of pigments that are yellow, orange, or red and are found in many fruits and vegetables, as well as in some photosynthetic tissues of plants. They play several roles in plant health and photosynthesis.

• Carotenoids absorb wavelengths of light that chlorophyll cannot, providing a more comprehensive range of light absorption for photosynthesis.
• They help protect plant tissues by dissipating excess light energy that could otherwise damage chlorophyll or interact with oxygen to produce harmful reactive oxygen species.

In paper chromatography, carotenoids can be separated based on their solubility in different solvents. Their distinct coloration makes them easy to identify on the chromatography paper once separated. Carotenoids include well-known compounds like beta-carotene, lycopene, and lutein, which are of significant interest not only for their role in plants but also for their antioxidant properties and potential health benefits to humans.