Materials and MethodsUse past tense, passive voice to describe what was done. i.e. "frogs were dissected", not "I dissected the frogs." Do NOT use imperative tense, as if giving instructions, as in the lab manual.
Materials and equipment used are mentioned in the course of describing the procedures. The sequence of events is implied by the order of your sentences. Therefore, you do not have to place the word "then" or "next" in each sentence.
A person with some background in the area should be able to repeat your experiment from the description of your methods. Assume the reader has some knowledge of biological techniques - do not bore him/her with excess detail and verbiage. Be clear and brief. Give no equations, calculations, conversions, or figures. Mention if class data were pooled.
Important facts to include here are how many individuals of each organism were used, their conditions of light and temperature (Celsius!), what they were fed, how long experiments were run, and things of this nature, which are likely to have a big impact on the results. Always use appropriate metric units -- force is not measured in millimeters