Name_______________________________________________________________________Date________
Lab: Air Pollution Assay
Honors Biology
Pre-Lab Questions:
1. What is the purpose of this lab?
2. Why are we using lichen? Explain in detail.
3. Where can lichen be found?
4. What type of indicator will be used in this lab and why?
5. What does the level of blue dye in the test tube indicate?
6. Why do you think you must rinse the disk with distilled water during the day 1 lab procedure?
7. What type of data will you be recording? Quantitative or qualitative? Explain.
8. In our last wet lab using indicators you had a positive and negative control. Will you have those in this
lab? If so, identify them.
9. Read through the lab and define any terms you have not heard of before in the space below (choose at
least 3 terms)
Introduction:
A lichen is a symbiotic association between a fungus and an alga. The lichen body (thallus) takes on a
form unlike that of either the fungus or the alga living independently. This fungal-algal partnership is capable of
survival in environments most other organisms would find tolerable. In fact, lichens are able to survive
conditions neither partner could tolerate alone-- lichens occur from the Arctic to the Antarctic. In the lichen
symbiosis, the fungus is supplied with carbohydrates, nitrogen compounds, and vitamins by the alga, while the
alga is protected from high light intensity and provided with water, minerals, and some organic nutrients. The
fungus is the dominant member of the team, forming an envelope around the algal component. The lichens,
therefore, are classified as fungi.
Figure 1- Three lichen types
There are three major growth forms of lichens: crustose (flat, adherent crusts), folios (leafy), and fruticose
(branched). The lichen supplied in this kit is a foliose lichen. The thallus of this type of lichen is composed
mainly of interwoven fungal hyphae (95% of the dry weight), while the algal component is limited to a
subsurface layer. Special fungal hyphae, the rhizinae, extend from the lower surface of the thallus to penetrate
the substrate for anchoring the thallus and absorbing water.
Lichens are extremely slow-growing (some grow only 1 mm to 1cm per year) and long-lived. If large numbers
for large lichens are found in an area, it can be assumed that they have been undisturbed for a long time.
Some Arctic lichens are estimated to be about 45000 years old.
Lichens are remarkable in their ability to withstand high and low temperatures, desiccation, mineral and
nutrient stress, extremes of light intensity, and all manner of hostile habitats. But they must have clean air-they cannot tolerate the polluted air of cities and industrial areas.
Several peculiarities of lichen structure explain their sensitivity to air pollutants. Since lichens are not rooted
like plants, they receive their nutrients and water mainly from the atmosphere. They have a very efficient
absorption system and therefore high levels of toxins accumulate within the. Their entire surface is exposed 24
hours a day to any chemicals in the atmosphere or substrate. Lichens have no cuticle or outer layer to protect
them from the gaseous environment or to reduce water loss. There are no stomata to shut out pollutants, nor
do lichens have deciduous parts that can be shed in the winter. Lichens accumulate cations from their
environments in excess of the biological requirements. It is not understood how lichens can tolerate such high
levels for individual metals. However, accumulated toxins slow growth, and when the system is overloaded
with toxic cations, the lichen dies.
Lichens absorb heavy metals from the atmosphere. Heavy metal fallout, especially from cadmium, copper,
lead, manganese, nickel, and zinc, results from smoke particulates from oil and coal combustion, from smelting
processes, and from vehicle exhausts. By methodically noting lichens’ occurrence and growth patterns in and
around industrialized areas, ecologists can create lichen maps that show patterns of air pollution.
Lichens inhabit a peculiar niche in nature that impacts on man and other organisms in a number of ways.
Lichens have long been recognized for their role in “building” soil from rock. They extract minerals such as
phosphorous, magnesium, calcium, iron, potassium, and sulfur from rock and deposit them in tiny rock
crevices. As the lichens die, their organic matter is added to the extracted nutrients, forming soil. Lichens
provide food, shelter, and camouflage to a variety of animals, protozoa, and bacteria. For many years litmus
paper was produced from lichens, but today their main industrial uses are in fixatives, alcoholic beverages,
perfumes, antibiotics, and other medicines.
Destruction of lichens not only indicates ecological damage but it can also cause some. Since lichens
accumulate radioactive metals as well as airborne pollutants, radioactive substances can enter to the food
chain through them. Lichens are the principal food of both reindeer and caribou, on which Laplanders adn
Inuits depend for food, clothing, and shelter. Also, since lichens help build soil from rocks, this process slows
when they are destroyed. Lichens also protect soil from erosion (vast tracts, in some regions) and help insulate
it.
Objectives:
● Understand the symbiotic structure of lichens and how it benefits both the algal and the fungal partner.
● Understand how lichens’ structure makes them susceptible to air pollution damage.
● Gain practice in controlled modeling and testing of a naturally-occurring phenomenon (extrapolate from
nature to lab and vice versa).
● Appreciate the scientific value of indicator species.
Materials:
● Lichen Sample
●
Distilled Water
●
7 Test Tubes
●
Paper Punch
●
Methylene Blue Solution, 60 mL
●
8 Graduated Cylinders (at least 10 mL)
●
Cadmium Chloride Solution, 30 mL
●
Strainer
●
Lead Chloride Solution, 30 mL
●
Small Plastic Cups or Glass Beakers
●
Lithium Chloride Solution, 30 mL
●
Test Tube Racks
●
Manganese Chloride Solution, 30 mL
●
Sodium Chloride Solution, 30 mL
●
Zinc Chloride Solution, 30 mL
●
Blue-Colored Glass Cleaner
Procedure:
Day 1: Preparing and Dying the Lichen Discs
1. Punch out disks of the lichen with a hand-held paper punch. Each group of students will need five disks
of lichen of roughly the same size. Any bark adhering to the lichen will not affect the outcome of the
exercise.
2. Drop the lichen disks into enough methylene blue solution to cover the disks. Force the disks down
under the surface of the methylene blue until they are thoroughly wet. Leave the disks in the dye for 30
minutes. Work on the pre-lab questions while you wait.
3. Remove the lichen disks from the dye by pouring the lichen disk/methylene blue mixture through a
strainer. Rinse the lichen disks with distilled water. Place your disks on a paper towel with your name
on it and put it in the bin for our class.
Day 2: Leaching of Methylene Blue
1. Measure out 10ml of your assigned substance using the graduated cylinder and place it into your test
tube.
2. Add the five disks and allow them to soak in your assigned solution for 30 mins. Gently shake the
cylinders every 5-10 mins.
3. Observe the color of the solutions during the 30 minute leaching process.
4. At the end of the 30 minutes, shake the tubes well and then compare the intensity of the blue color of
each solution to the distilled water and the blue glass cleaner. Score the blue glass cleaner as ++++
and the distilled water as -. Evaluate the color intensity for each metal solution and assign them values
ranging from - to ++++ after comparing each to the water and the blue glass cleaner.
5. Collate the data in Table 1 and compare with the expected results in Table 2.
Data
Table 1: Intensity of Color Leached from Lichen Disks
Solution
Cadmium Chloride
Lead Chloride
Lithium Chloride
Manganese Chloride
Sodium Chloride
Zinc Chloride
Distilled Water
Blue-colored Glass cleaner
Intensity of Blue Color
*Interpretation of Results
It has been known for some time that fungal cell walls strongly bind metal cations. Lichens trap metals
by an ion exchange process in which chemical sites on the cell wall release hydrogen ions and bind
metal cations. In this exercise, the lichen binding sites are saturated with methylene blue molecules,
which have a positive charge but are more weakly held by the binding sites than metal cations are. Any
subsequent replacement of methylene blue by metal cations is indicated by the amount of methylene
blue leached from the lichen after exposure to the metal cations. Notice whether you see any
correlation between the valence of the metal cation and the amount of leaching seen.
Post Lab Questions:
1. Which chemical solution replaces the most methylene blue? What does this indicate?
2. Do your experimental results support the claim that lichens absorb toxins? Explain.
3. Lichens are extremely slow-growing and long-lived organisms. Some are considered to be thousands
of years old. Besides the air quality, what could the absences of lichens from an area indicate?
4. Lichens are also known to provide food, shelter, and camouflage to a variety of animals. Humans can
use these animals for food, clothing, and shelter. What are some implications to the food web of lichens
absorbing heavy metals?
5. Write a conclusion paragraph for this lab in the space below. Include your results, what they infer, and
any sources of error for the lab.