Using the technique of synchronous culture, investigations were made of the effects of temperature and light-intensity on cellular life cycle ofChlorella ellipsoidea. Some improvements in the culture technique for obtaining a good synchrony of algal growth were described.By following the changes of average cell volume and cell number occurring during culturing, the rates of the following processes of life cycle were determined: (i)“growth”(or the increase in cell mass) occurring from the stage ofsmaller cells(Da) to the stage ofripened cell(L3), (ii)“ripening”(or processof formation of“nuclear substances”as estimated from the average number of daughter cells formed from single mother cell), and (iii)“maturing and division”which leads to the full maturation of mother cells (L-cells) and their division into separate daughter cells (D-cells).“Growth”and“ripening”were found to be dependent in light,“maturing and division”light-independent. The time required for“growth”and“ripening”(τC) is dependent on temperature but independent of light intensity, the onset of“maturing and division”occurring at the same time (τD) of culturing under varied light intensities. The average cell volume at this stage (L3),however, was found to be markedly modified by light intensity; larger with higher temperatures (see Fig. 4).Changes in incubation temperature (under the condition of saturating light intensities) were found to affect the life cycle in the following way: (i) The time of onset of“maturing and division”(τD), varies markedly with culturing temperature; earlier at higher temperatures, (ii) The average cell volume at this stage also depends on temperature ; smaller at higher temperatures.The average number of daughter cells (n) emerging from single mother cells, was found to be uninfluenced by culturing temperature; (4.0–4.1 under the conditions of the present study). It was found that the division numbernis remarkably varied by changing the light intensity in the“growth”and“ripening”phases; 2.0 at 1 kilolux, 3.7 at 5 kilolux, 4.2 at saturating light intensities (10 and 25 kilolux). This finding was explained by assuming a light-dependent formation of“nuclear substances”during the“growth”and“ripening”phases, the quantity of the substances in the cell at L3stage determinig the division number.The experimental data were analyzed reaction kinetically, the rate constants and other characteristics of the reactions constituting the processes of life cycle were determined, and values for the apparent activation energy for each reaction were computed. The reactions were discussed with special refer
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