= Solution
Use a <randomized complete block design>, with day as block and each <biological cell> as an <experimental unit>. \b[Each day should contain two <biological cells> at each of the five dose levels.] Each level then has ten <replicates> overall and occurs equally often in every day: the resulting <block design> is an <orthogonal block design>.
This spreads any day-to-day changes in preparation, temperature or measurement across all levels instead of <confounding> dose with day. Treat the zero level as a control with otherwise comparable handling. Keep the treatment-to-measurement delay standardized because the <response variable> is a <diffusion> rate measured immediately after preparation.
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