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Most of the paper should be written in the PAST TENSE (was, were).
The present tense (is, are) is used when stating generalizations or conclusions.
) If the title had been "Effect of Environmental Factors on Growth of Escherichia coli ", the reader would not know which environmental factors were manipulated.
If the title had been "Effects of Light and Temperature on the Growth of an Organism", then the reader would not know which organism was studied.