This lab activity is about toxic substances like pesticides and their effects on biological systems. The activity starts with an introduction of how birds sequester calcium to make an egg. Learners are asked to bring eggshells from home from different kinds of birds, if possible. These shells are prepared for analysis. Learners discover how to prepare a primary acid, neutralize a base, and calculate the percentage of CaCO3 in shell material. These results lead to a discussion of how calcium moves through this biochemical system and how a pesticide can prevent calcium from building eggshell. This resource includes tips, some related to safety; adult supervision recommended.