AP® Environmental Science: Environmental Pollution and Lichens

Product Details

Overview 
In this inquiry lab, students discover the value of lichens as living indicators of environmental quality. In Part I, students soak lichen pieces in methylene blue solution, which is absorbed by the lichen. In Part II, students place the methylene blue-soaked lichen into test tubes containing different metal cation solutions (sodium, potassium, copper, cobalt, iron, and distilled water as a control). As the lichen absorbs the metal cations, it releases the methylene blue back into solution. By comparing the intensity of the blue color across solutions, students determine which metal cations are most readily absorbed by lichens and which would have the greatest environmental impact. 

AP® Course and Exam Description Alignment 
This activity is aligned to the 2024 AP® Environmental Science Course and Exam Description, Unit 7: Atmospheric Pollution.  

Learning Objectives addressed: 
● STB-2.A: Identify the sources and effects of air pollutants. 
● STB-2.B: Explain the causes and effects of photochemical smog and methods to reduce it. 
● STB-2.G: Explain how air pollutants can be reduced at the source. 

Science Practices addressed:  

SP 1.A, 1.B (Describe and explain environmental concepts and processes) 

SP 4.C (Describe an aspect of a research method) 

SP 5.D (Interpret experimental data and results and explain what the data implies about environmental issues) 

SP 7.A, 7.B (Describe environmental problems and potential responses). 

Exam Connect questions are included, featuring both free-response and multiple-choice questions aligned to Unit 7 topics and science practices. 

Key Features 

Real sample data included. Kit instructions always include real sample data—never made up! Teachers have a complete cation exchange data table with intensity ratings for all six solutions to guide expectations. 

Tested and optimized. Each experiment has been thoroughly tested, retested, and optimized to guarantee safety and success. 

Prelab questions build foundational understanding of mutualism, indicator species, and pollution sources. A two-part guided procedure walks students through lichen preparation and cation exchange experimentation, and post-lab questions progress from explaining the exchange mechanism to data interpretation to proposing environmental solutions. 

Flexible and adaptable. Additional lichens can be collected locally for extended testing. The activity can be expanded into a field study where students survey lichen populations in their area to assess local environmental quality. 

Teacher Notes 
Estimated Time: This lab can be completed in two 50-minute class periods. Day 1: soak lichen in methylene blue for 30 minutes, then rinse with distilled water. Day 2: soak lichen in metal cation solutions for 30 minutes and evaluate the exchange. 

Kit accommodates 15 groups of students. 

Materials: Kit includes methylene blue solution, potassium chloride solution, sodium chloride solution, copper(II) chloride solution, cobalt chloride solution, iron(III) chloride solution, foliose lichen, gauze, and culture tubes. 

Additional Materials: Distilled water; scissors; stirring rod; test tube rack. 

Advanced Preparation: Teacher may presoak the lichen in methylene blue for 30 minutes before class to complete the activity in one period. It is not recommended to soak longer. Gauze can be precut into pieces for rinsing. 

Safety: Cobalt chloride is moderately toxic by ingestion. Iron(III) chloride may be irritating to skin and body tissue. Copper(II) chloride is toxic by ingestion and inhalation. Methylene blue will stain skin, clothing, and surfaces. Wear chemical splash goggles, chemical-resistant gloves, and a chemical-resistant apron.