Plant Pigment Chromatography
Plant Pigment Chromatography
1. Describe what each of your chromatography strips looked like. Specifically, identify the pigments on each strip and compare their positions to one another. Plants have four types of pigments, namely chlorophyll, carotenoids, anthocyanins, and xanthophylls. These pigments have different polarities and chemical properties. In paper chromatography, the pigments will separate based on their affinity to the medium (paper), and affinity for the solvent. The solvents used in this experiment are water (polar) and acetone (mid-polar). Therefore, the different pigments will migrate based on their respective polarities too.
The pattern of migration will be similar for acetone and distilled water. The fastest to migrate (or found at the topmost of the paper strip) will be anthocyanin, followed by carotenoids, then xanthophylls and lastly chlorophyll. Chlorophyll is insoluble in polar solvents therefore it will migrate slowest in both water and acetone and will be found closest to the bottom of the paper strip. 2. Which pigments did the spinach and the red leaf lettuce have in common? Propose an explanation for this. Spinach and red lettuce will have the same pigments, only they will be in different concentrations.
Plants have different pigments to maximize their photosynthesizing capability. With different pigments, all the photosynthetically active radiation emitted by the different light wavelengths will be absorbed. For example, the green pigment chlorophyll will not absorb the green wavelength; therefore, the carotenoids and the xanthophylls will absorb light in that region to increase absorption rate. 3. Which pigments were soluble in water? In acetone? Why are some pigments carried further from their original position than others? Chlorophyll is not soluble in water and only slightly soluble in acetone.
Carotenes and anthocyanins are highly soluble in water. Some pigments travel further away from their original position compared to others because these specific pigments are more soluble in water or acetone than the others are. The differences in solubility are attributed to their different chemical structures and composition. 4. In the fall, leaves often change colours as the day shortens. Propose an explanation for this colour change. What do you think happens to the green pigments? Why don’t we see the other pigments during the summer? In some trees, changes in leaf colour occur in autumn.
Changes in day and night temperatures, daylength and light intensity will signal that autumn is about to set in. In autumn, the production of food, through the process of photosynthesis, is minimized to conserve energy and resources. With this, the plant will stop manufacturing chlorophyll, the photosynthetic pigment responsible for the green colour in plants. Without any chlorophyll, the other pigments that are present in the leaf, like anthocyanin and carotene, become exposed. These pigments do not absorb red and yellow in the light spectrum, therefore leaves with high carotenes show yellow, red, and orange colours.
5. Which pigments are most crucial to plant survival? Outline the functions of these pigments. Chlorophyll a and b are the pigments that are most crucial to the survival of the plants. These two pigments are present in the highest amount in the leaves compared to other pigments. The pigments absorb light and transmit the energy from this light to other chlorophyll molecules towards the photochemical reaction centre in the dark reaction phase of photosynthesis (Mathews & Van Holde, 1996). Chlorophyll therefore plays a very important role in photosynthesis.
Conclusion Plants have a large number of pigments to carry out photosynthesis to ensure that the absorption of photosynthetically active radiation (PAR) is maximized. Individually, the different pigments will absorb only a certain range of wavelengths in the PAR. For example, chlorophyll will not absorb the blue green region while carotenoids will try to absorb energy in the green region of the light spectra. References Mathews, C. K. , & Van Holde, K. (1996). Biochemistry (Second ed. ). Menlo Park: The Benjamin Cummings Publishing Company, Inc. ,.