This unit introduces students to the properties of cell membranes and how substances are transported across the cell membranes of plants and animals. Designed to familiarize the students with the concepts related to membrane permeability, each of the five exercises involve the students’ skills of observation. The students will find the exercises easy to follow and comprehend. Each exercise is followed by a series of questions to help students learn how to think critically about biological topics. At the end of the unit, there are additional questions to review the most important points of the unit and to relate the unit to the students’ everyday life.