Effect of Light Color on Plants

Topics: Photosynthesis, Plant, Color Pages: 5 (1615 words) Published: January 5, 2012
Living organisms have been classified by humans according to several different characteristics, one of them being the manner in which they obtain nutritive organic molecules (1), in other words, their food. Plants are denominated as autotrophs, organisms that can produce their own food from abiotic sources surrounding them, such as light, carbon dioxide and water (2). Plants use these three factors in photosynthesis to convert light energy into chemical energy, which is then stored until the plant needs it, or used right away (3). The process of photosynthesis takes place on organelles (substructures inside eukaryotic cells) called chloroplasts, more specifically, on the membrane of the thylakoids inside the chloroplasts, where protein complexes known as photosystems are situated. It’s these complexes that are responsible for the photosynthetic processes. Because this is the main way in which plants obtain their food, and light energy is the base of said process, light is absolutely essential for their growth. Sunlight contains many different wavelengths which, when isolated, present different colors of visible light. Plants cannot use all wavelengths of light, however, because the different chlorophylls (pigments in the plants’ chloroplasts, also responsible for photosynthesis) absorb and use only certain wavelengths of light ; the rest is reflected back out, unused (4). Exposed to sunlight, plants have available to them, a range of wavelengths wider than the light spectrum visible to us, from which they utilize only a select range for photosynthesizing. This essay will investigate the effect light color/wavelength has on plant germination and rate of photosynthesis. Cellophane sheets of different colors (red, yellow, blue, green) and clear plastic wrap were used to provide these limited wavelengths . The experiments dealing with germination consisted of different seeds being planted separately from other species and being covered by the different colored cellophane or the clear wrap; they were then watered and monitored for a week, taking note of any growth. The plants used were the common bean (Phaseolus vulgaris), brown mustard (Brassica juncea), and common oats (Avena sativa). For the photosynthesis rate experiment, same sized Brazilian waterweeds (Egeria densa) were inserted in eudiometer tubes filled with water and then placed in a beaker half-filled with water. Each test tube was wrapped with a different color, and the volume of oxygen produced, through photosynthesis, by each of the plants was compared. Beans, specifically all the plants under the genus Phaseolus, are amongst the fastest growing plants and are said to germinate within a week. To make them germinate faster, it’s usually recommended to soak them in water before planting because hydrating the seeds stimulates germination. (5) They also benefit from warm temperatures because they are native to more tropical climates (6). They need to be planted in well drained soil because they aren’t tolerant to water excess. Mustard is also among the fastest sprouting plants, but its growth afterwards is relatively slow as it’s meant to grow flower buds five weeks later. It does better in cool conditions than warm and can usually withstand short periods of mild drought with little to now consequences. In addition, it too, is not tolerant to water clogging in the soil (7). Oats are native to warm, sub-tropical regions and can manage well in poor soils (8) but they also require good water draining . The Experiments


Fifteen equally sized plastic containers (cylindrical in shape, approximately 8cm in diameter and 6cm in height) were filled with the same amount of soil. Five of them were allotted to each plant species; making sure to add the same amount of seeds in each segment (comparing to the same species, since the size of the beans and oats is much greater than the brown mustard seeds and would therefore be unreasonable to compare their...
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