Determine the relationship between light intensity and the rate of photosynthesis in spinach leaves.

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Abstract:

This study was undertaken to determine the relationship between of light intensity and rate of photosynthesis in spinach leaves.  Rate of photosynthesis was determined at pH 7,  0.2% NaHCO3, room temperature, and under white light using light intensities of 2200, 4250, 5300, 14400, 20600 lux.  The amount of oxygen production was determined after five minutes at each light intensity.  Spinach leaf segments were infiltrated with 0.2% NaHCO3 and made to sink in solutions of 0.2% NaHCO3 so that rate of oxygen , production could be estimated from the rate at which the leaf segments floated.  The rate of oxygen production increased relatively rapidly at lower light intensities but leveled off at intensities greater than 5300 lux, suggesting that light intensity is a limiting factor of photosynthesis below 5300 lux.  At light intensities greater then 5300, however, light intensity is no longer limiting.  Instead other factors such as amount of water, NaHCO3, chlorophyll, and other reagents of photosynthesis become limiting.  

Introduction:

Photosynthesis is a process that underlies all life on Earth.  It is essential in creating the sugars that sustain life.  By converting light energy into chemical energy in the form of carbohydrates, it not only sustains the life of photosynthetic organisms themselves (called autotrophs), but also provides food for the heterotrophs that consume autotrophs.  

        The net reaction of photosynthesis is

CO2 + H2O + light energy yields (CH2O) + H2O + O2

where (CH2O) stands for carbohydrate.  Overall, photosynthesis consists of two sets of reactions: one that is light dependent and one that is independent of light.  In the light dependent reactions use energy from light is absorbed by chlorophyll.  This powers the release of electrons from water, which are then transferred to the electron carrier, NADPH.  Oxygen is a product of the light dependent reactions.  In contrast, the light-independent reactions result in the production of sugar from carbon dioxide.  

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        It is useful to study factors that affect rate of photosynthesis in order to determine the conditions of optimal photosynthetic activity and explain various characteristics of plants.  For example, understanding the affect of light intensity on rate of photosynthesis may reveal why shrubs in the shade do not grow as tall as trees with greater exposure to sunlight.  

        In this experiment, spinach leaves were subjected to varying light intensities to determine the effect of light intensity on rate of photosynthesis as measured by production of oxygen.  We expected rate of photosynthesis to increase with increasing light intensity.  This was ...

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