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LIGHT INTENSITY ENHANCES PLANT GROWTH IN RCBr ( Brassica rapa ) FAST PLANTS Laurent King (320) 266-3780 Day 4/2:40 P.M/Dr. S. Saupe 14 April, 2008 Introduction Plant biologists and environmentalists alike have been interested in the effects of light, among other important environmental conditions, on plant growth. The effect of varying light intensity should be studied in order to understand the natural conditions that plants are exposed to throughout the day, during which the plant experiences rapid changes in light quality and intensity (Huxley, 1969). Light is important in the plant for photosynthesis, which is the means by which the energy from light is captured and used to synthesize chemical energy in the form of carbohydrates (Brooker et al., 2008). The plant uses these carbohydrates as a source of nutrition to support healthy growth. However, this experiment will focus on RCBr ( Brassica rapa ) fast plants. In plants, photosynthesis occurs in the chloroplasts in two reaction stages: light dependent (light reaction) and light independent (dark reaction). Although the products of the light dependent reaction are used in order to carry out the light independent reaction, light is especially important in the light dependent reaction. The light reactions involve an amazing series of energy conversions, starting with light energy and ending with chemical energy in the form of covalent bonds (Brooker et al., 2008). The light-dependent reactions take place on the thylakoid membranes of the chloroplast using four membrane-bound protein complexes called
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photosystem I (PSI), photosystem II (PSII), cytochrome complex (C) and ferredoxin complex (FD). In these reactions light energy is used to split water, oxygen is given off, and ATP and NADPH are produced. Photosystem II (PSII) is the initial step in the light dependent reactions of photosynthesis, and it has two main components: a light harvesting complex and a reaction center. The light harvesting complex is composed of several pigment molecules attached to proteins, and its role is to directly absorb ‘harvest’ photons of light. When a pigment molecule absorbs a photon, electrons are boosted or excited to a higher energy level. This energy is then transferred to a special pigment molecule (P680), located in the reaction center of PSII, and known as so because it is best at absorbing light at a wavelength of 680 nm. When an electron in the P680 pigment molecule is excited it is then designated P680*. The reaction center then quickly removes the high-energy electron from P680* and transfers it to another molecule known as the primary electron acceptor where the electron will be more stable. It also replaces the electrons removed from the pigment molecules with electrons from water molecules, and transfers those electrons to oxidized pigment molecules (P680 + ). The oxidation of water results in the formation of oxygen gas (O 2 ), which is then released into the atmosphere. Once the primary electron acceptor has
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This lab report was uploaded on 04/17/2008 for the course BIOL 221 taught by Professor Saupe during the Spring '08 term at CSB-SJU.

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