Lab 4: Cell Structure, is one of a series of lab investigations for the middle school student from the book, "Argument-Driven Inquiry in Life Science: Lab Investigations for Grades 6-8". Students are introduced to The Cell Theory, design a simple experiment, and engage in argumentation. "Checkout Questions" are provided to facilitate student reflection on what was learned. Students are assigned a short investigation report to finish processing their experience. Significant background information is provided for teachers and to a lesser degree in the student hand-out in the introduction. The standards addressed in the lesson are also included in the teacher's notes.