Activity Overview

Mold Control: Toxicology Experiment

Activity Overview

Disciplines Covered: Science & Math

Prep Time: 60-90 minutes

Activity time: 2 class periods, plus incubation time (about 3-5 days)


The Dose Makes the Poison

LOEL

LD100

LD50

100

0

% Mortality

LD 50: Lethal Dose 50%

LD 100: Lethal Dose 100%

LOEL: Lowest Observable Effect Level


Serial Dilution Schematic


Serial Dilution Preparation

Teacher: Yeast dilutions Three batches of 10-5 yeast solution

Students: Cleaners- 100% to 0.0001%Group A – Lysol Kitchen Antibacterial Cleaner

Group B – Tilex Mildew Remover

Group C- Borax


Yeast Serial Dilutions


Add yeast solution to film


Lay film cover down


Press with spreader


1 ml spread on film


Incubate in bag


Petrifilm after Incubation


Part I: Serial dilutions

Working in pairs, you have 10 minutes to complete this task:

1. Practice using the disposable pipette with colored water.

2. Create a 10-6 dilution of yeasta. Mix the 10-5 yeast dilution well.b. Using a pipette, take 1 ml from

10 yeast dilution.c. Add this to the 9 ml of water in

the blank tube.d. Label this new dilution “10-6” e. Mix well.


Part II: Petrifilms

You have 5 minutes to complete this task. Working in pairs:

1. Mix your 10-6 dilution well.2. Draw 1 ml of your solution into a

NEW disposable pipette.3. Take one 3M Yeast and Mold

petrifilm.4. Lift the plastic layer.5. Squeeze out the 1 ml into one

large drop in the middle of the grid6. Lay the plastic layer back down.7. Place the spreader over the middle

of the drop. 8. Press down with firm pressure for

about 5 seconds.


Potato Dextrose Agar Plates

• An alternative to 3M Yeast and Mold Petrifilms are the traditional agar plates.

• Potato dextrose agar is used because it is a good medium for growing yeast.

• The alternative student and teacher materials are available on the Hydroville website: www.hydroville.org


Yeast solution and plate


Draw up about 0.5 ml


Add 4 drops to plate


Spread with back of spoon


Liquid on agar


Incubate upside down


Agar plate after Incubation

Control vs. 100% Lysol


Counting Colonies

Mold Control: Toxicology Experiment Part III: Data Analysis and Interpretation

You have 10 minutes to complete this task.

1. Work together to count the colonies on the petrifilms for each dilution (Tilex, Lysol, or Borax).

2. Plot your data on the graphs provided.

3. Find the LOEL and LD50 on the dose-response curve.

4. Compare answers with other groups to determine which cleaner is the most effective.


Calculations

% killed = C-T x 100 C

T= Number of colonies in treatment

C= Number of colonies in control


Results

Percent Killed

Dilution Lysol Tilex Borax

0.0001% 2 0 0

0.001% 2 2 0

0.01% 0 56 0

0.10% 34 91 0

1% 61 100 0

10% 91 100 19

100% 100 100 50


Dose-Response Curve

Mold Control Results

0.0

25.0

50.0

75.0

100.0

0.0001 0.01 1 100

Percent Concentration (log scale)

Perc

ent k

illed Lysol

Tilex

Borax


Student Outcomes

After doing this activity, students will be able to:

•Develop a dose-response curve.

•Identify the Lowest Observable Effect Level (LOEL), LD100 and LD50 on the dose-response curve.

•Understand the effect disinfectants have on yeast growth.

•Understand the purpose of using an experimental control.

Documents

Activity Overview