Teacher Notes

Environmental Pollution and Lichens

Student Laboratory Kit

Materials Included In Kit

Cobalt chloride solution, CoCl2•6H2O, 0.01 M, 100 mL
Copper(II) chloride solution, CuCl2•2H2O, 0.01 M, 100 mL
Iron(III) chloride solution, FeCl3•6H2O, 0.01 M, 100 mL
Methylene blue solution, 5 x 10–4 M, 100 mL
Potassium chloride solution, KCl, 0.01 M, 100 mL
Sodium chloride solution, NaCl, 0.01 M, 100 mL
Foliose lichen, approximately 27 in.2*
Gauze, 1 roll
Test tubes, 120
*May be in multiple pieces, so excess is included.

Additional Materials Required

Water, distilled
Scissors
Stirring rod
Test tube rack

Safety Precautions

Cobalt chloride is moderately toxic by ingestion. Iron(III) chloride solution 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. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Disposal

Please consult your current Flinn Scientific Catalog/Reference Manual for general guidelines and specific procedures, and review all federal, state and local regulations that may apply, before proceeding. The cobalt chloride solution may be treated according to Flinn Suggested Disposal Method #27f. The potassium chloride, sodium chloride, copper(II), and iron(III) chloride solutions may be flushed down the drain with excess water according to Flinn Suggested Disposal Method #26b.

Teacher Tips

  • Enough materials are provided in this kit for 30 students working in pairs or for 15 groups of students.
  • The lichen samples by be broken into small pieces by hand. The bark may be left on the lichen pieces if necessary. The bark will not affect the result.
  • In order to save time, the lichens may be pre-soaked in the methylene blue solution by the instructor before students come to class or this activity may be broken into two class periods.
  • Incorporate lichens into your lesson plans before beginning this activity. Introduce the three types of lichens: foliose (leafy), fruticose (branched) and crustose (flat crust).
  • Additional lichens may be collected in your area for testing. The best lichens to use are foliose lichens. They are usually bluish-green or bluish gray and grow on rocks and trees.
  • As an extra credit project, have students look for lichens in your area and write a report on the overall environmental quality pertaining to their findings.

Further Extensions

  • As an extra credit project, have students look for lichens in your area and write a report on the overall environmental quality pertaining to their findings.
Alignment with AP® Environmental Science Topics and Scoring Components

Topic: Pollution. Impacts on the Environment and Human Health (Hazardous chemicals in the environment).
Scoring Component: 9-Pollution, Hazardous Chemicals in the Environment.

Correlation to Next Generation Science Standards (NGSS)†

Science & Engineering Practices

Planning and carrying out investigations
Analyzing and interpreting data

Disciplinary Core Ideas

MS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience
HS-LS2.C: Ecosystem Dynamics, Functioning, and Resilience

Crosscutting Concepts

Stability and change
Patterns
Cause and effect

Performance Expectations

HS-ESS1-4: Use mathematical or computational representations to predict the motion of orbiting objects in the solar system.

Sample Data

{13917_Data_Table_1}

Answers to Questions

  1. What is a lichen?

    Lichens consist of fungal threads and microscopic green algae living together symbiotically and functioning as a single organism.

  2. Which solution indicated the least amount of methylene blue exchange?

    The solution containing sodium had the lowest methylene blue exchange although water is a very close second. This is likely due to the carbonic acid content in our deionized water. Carbonic acid forms as carbon dioxide diffuses into the deionized water and creates a slightly acidic solution. In your area, tap water may have a lower methylene blue exchange.

  3. Which solution indicated the greatest amount of methylene blue exchange?

    The iron(III) chloride solution had the highest methylene blue exchange.

  4. Given the results, which metal cation would have the greatest effect on lichens?

    The iron cation would affect lichens the most.

  5. What possible things could be done to stop lichen deterioration in your area?

    Answers will vary.

Recommended Products

Item No. Description
AP6461 Environmental Pollution and Lichens, Full-Size Lab Kit
LM1028 Lichen Set—3 Types

Student Pages

Environmental Pollution and Lichens

Introduction

What is a lichen? Can lichens really be used as an indication of the quality of the environment? Perform the following experiment and find out!

Concepts

  • Environmental pollution
  • Natural indicators
  • Lichens

Background

Lichens consist of fungal threads and microscopic green algae living together symbiotically and functioning as a single organism. Symbiosis is defined as the condition when two or more dissimilar organisms live together in close association. In this case, the symbiosis is mutualistic since both organisms benefit from the relationship. The main body of a lichen is called a thallus and does not resemble either algal or fungal structures. The algae within the thallus manufacture sugar that the fungus can feed upon. In return, the fungus provides protection for the algae.

As early as the mid-19th century, scientists became aware that lichens were becoming uncommon in areas in close proximity to cities. In 1866, William Nylander, a Finnish naturalist, was the first person to link the disappearance of lichens in urban areas to air pollution. He noticed that lichen species within the Luxembourg Gardens in Paris were missing in other parts of the city. Over the next three decades, the entire lichen population in the gardens was eventually wiped out by the large amount of industrial smog.

Why are lichens so sensitive to pollution? Lichens lack roots and act like sponges, taking in and retaining everything that is in the air and dissolved in rainwater. They also lack specialized protective surfaces, which could potentially block out harmful compounds. As pollutants reach high enough levels in lichens, the chlorophyll in the algal portion eventually breaks down and photosynthesis stops. This results in death of the algae which, in turn, results in the death of the fungal component of the lichen.

Due to the susceptibility of lichens to pollution, they are commonly used as bioindicators of the quality of the environment. The presence or absence of lichens in a given area can be easily recorded and can be used to indicate changes in the environment over a period of time. In fact, lichens are used as a means of assessing pollution from radionuclitides that are released near uranium mines, crashed satellites, etc. Lichens have also been used to test the fallout of radioactive dust from nuclear explosions, and were used following the nuclear disaster at Chernobyl in 1985 to render the meat of the caribou that fed upon the lichens unsafe for human consumption.

Metal cations are also a source of pollution that affect the life cycles of lichens. Metal cations commonly enter the environment from air pollutants, highway salt treatments and chemical dumping to name a few. In this activity, pieces of lichens will be used as bioindicators to show and quantify the detrimental environmental effects of several different metal cations.

Materials

Cobalt chloride solution, CoCl2•6H2O, 0.01 M, 2.5 mL
Copper(II) chloride solution, CuCl2•2H2O, 0.01 M, 2.5 mL
Iron(III) chloride solution, FeCl3•6H2O, 0.01 M, 2.5 mL
Methylene blue solution, 5 x 10–4 M, ~ 5 mL
Potassium chloride solution, KCl, 0.01 M, 2.5 mL
Sodium chloride solution, NaCl, 0.01 M, 2.5 mL
Water, distilled
Gauze, ≈ 2" x 3" piece
Lichen pieces, approximately 1 cm x 1 cm, 6
Stirring rod
Test tubes, 7
Test tube rack

Safety Precautions

Cobalt chloride solution is moderately toxic by ingestion. Iron(III) chloride solution 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. Please review current Safety Data Sheets for additional safety, handling and disposal information.

Procedure

  1. Place 5 mL of the methylene blue solution into a test tube.
  2. Cut or break off 6 small pieces of lichen, approximately, 1 cm x 1 cm.
  3. Place the 6 pieces of lichen into the test tube containing the methylene blue.
  4. Allow the lichen pieces to soak for 30 minutes. If the lichen pieces float to the top, push them back into the solution with a stirring rod.
  5. After 30 minutes of soaking, remove the lichen pieces and place them onto a piece of gauze. Over or in a sink, lightly rinse the lichen pieces with distilled water.
  6. Obtain six clean test tubes. Place 2.5 mL of the appropriate solution in the test tubes according to the following chart:
    {13917_Procedure_Table_1}
  7. Place one methylene blue–soaked lichen piece in each test tube and let soak for 30 minutes. During this period, the methlyene blue cations previously absorbed by the lichens will be released as the metal cations are absorbed in exchange and enter the lichens. Shake or stir the solutions to dispense the methylene blue. The larger the cation exchange of the metal the more methylene blue will leave the lichens and enter the solution. Therefore, the intensity of the blue color of the solution should increase in proportion to the amount of the metal cations that have entered the lichens.
  8. After soaking, remove the lichens from the test tubes. Compare the intensities of the solutions. Rate the intensities of the blue solutions on a scale from 0–5 with 0 being colorless and 5 the most intense blue. Record your observations in the data table.

Student Worksheet PDF

13917_Student1.pdf

*Advanced Placement and AP are registered trademarks of the College Board, which was not involved in the production of, and does not endorse, these products.

†Next Generation Science Standards and NGSS are registered trademarks of Achieve. Neither Achieve nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.