Photosynthesis Formal Lab Report

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Introduction

The purpose of this lab is to determine which pigments in a plant support or effect photosynthesis, based on starch production, which wavelengths of light are involved in photosynthesis, and identify plant pigments found in a plant leaf by means of paper chromatography.

Life on Earth is dependent entirely on the energy from the Sun, not only to keep the planet at a suitable temperature but also to provide the energy required to sustain life. The energy of the Sun, in the form of photons, is actively captured by chlorophyll and related pigments present in photosynthetic organisms, like plants and algae. This captured energy is used to convert carbon dioxide into complex energy-rich molecules that can be used by themselves or other organisms.

“Photosynthesis is the conversion of light energy to chemical energy in the form of sugar and other organic molecules.” (Russell, Wolfe, Hertz, & Starr, 2010). Photosynthesis can be categorized into two main processes: light-dependant reactions and light-independent reactions. For the purpose of this lab, light-dependant reactions will be investigated. The reactants involved in photosynthesis include carbon dioxide, water and sunlight to produce glucose, oxygen, and water. The light reactions involve the capture and use of light energy by pigment molecules to synthesize NADPH and ATP. Plants use this light energy to produce glucose from carbon dioxide. The glucose is stored mainly in the form of starch granules, in the chloroplasts of cells. Glucose in the form of starch is non-polar and is not soluble in water, allowing it to be stored much more compactly. The chloroplast is formed from an outer membrane, an inner membrane, and an intermembrane compartment. The aqueous environment within the inner membrane is called the stroma. Within the stroma is the thylakoids, which are flattened, closed sacs. It is in these sacs that the specific molecules required to carry out the light reactions of photosynthesis are contained, including the pigments, electron transfer carriers, and the ATP synthase enzymes for ATP production.

A pigment is able to absorb photons of light and differ by the wavelengths of light they can absorb. The amount of energy in a photon is inversely related to its wavelength. Blue light has a shorter wavelength and consists of photons that have higher energy than the longer wavelength red light. When photons of light hit an object, they can be reflected off the object, transmitted through the object or absorbed by the object. The absorption of light by a pigment results in electrons becoming excited and moving to a higher energy state. Colour is determined by the wavelengths that it cannot absorb, therefore chlorophyll is green since it does not absorb green light. If a pigment absorbs all wavelengths of visible light, the object appears black. A large variety of pigments can be found in plants. The most common are chlorophylls a and b and carotenoids, located in the chloroplasts of cells, and anthyocyanins, located in the cell vacuoles and do not contribute to photosynthesis. Each of these pigments has different properties and performs different functions for the plant, including absorbing light in different parts of the spectrum. The more light absorbed equals the more energy available for a plant. The pigment molecules that can be found in plants are specifically arranged in and around photosystems that are embedded in the thylakoid membranes of chloroplasts. Each contains a reaction centre surrounded by an antenna complex. Light from the sun travels into the chloroplast and goes through the antenna pigment. The energy trapped by the antenna complex is funnelled to the reaction centre, called P700, where it is used to oxidize a chlorophyll molecule and donate an electron to a primary acceptor molecule to continue into carbon fixation to ultimately release glucose sugar (Oracle ThinkQuest, 2010). The reaction centers are named after the wavelength...
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