The Effects of Light Intensity on the Growth Rates of Green Algae

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In a given algal suspension optical density is proportional to the density of the algal population in terms of cell numbers or cell protoplasm per volume of the suspension. In using optical density as a measure of growth the assumption is made that as long as the culture is in the exponential phase of growth under steady state conditions the proportionality between optical density and the density of algal population remains constant. Growth rate, k, is caleulated from the integrated growth equation:

g_ O.D.0 tx'



where O.D.0 and O.D.1 are optical densities at the beginning and end of the time interval, t. By using logarithms to the base 2, and the unit of time as one day, the growth constant, k, becomes equivalent to the number of doublings per day. At least five readings were taken during exponential growth in each experiment at a particular light intensity. Reproducibility of the rate for at least two subsequent experiments was required. The logarithmic growth rate for each light intensity was calculated as an average from two experiments, each experiment conducted in duplicate.
RESULTS 2 give the growth rates of five algae Figures and plotted against light intensities up to 10,000 ft-c. Each of the light intensity curves consists of two portions. Illumination up to 2,000 ft-c was provided by fluorescent lamps. Intensities above 2,000 ft-c were from incandescent lamps. The shapes of the curves might not be
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