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Bioassay Investigations with Daphnia


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Bioassay Investigations with Daphnia
Developed by Kathy Cahill

Wantagh High School

Wantagh, New York

For the


My Environment, My Health, My Choices project

University of Rochester

Rochester, NY
Abstract:
A bioassay is used to study the effects of environmental changes on simple organisms. Students will investigate the response of Daphnia to exposure to various concentrations of toxicants. Data is graphed to create a “dose-response curve” and to determine the LD50 for the toxicant. Discussion questions encourage students to consider the implications of this research for potential short-term and long-term effects of toxicants on human health.
Table of Contents


Pre/Post Test

3-4

Pre/Post Test Answer Key

5-6

Learning Context

7

Teacher Background Information

7-11

Student: Introduction to Bioassays

12-15

Student: Investigating the Effects of Toxicants on Daphnia

16-18

Student: Inquiry—Investigating the Effects of a Toxicant on Daphnia

19-21

Teacher Resources

22

New York State Learning Standards

23

Appendix A: Alternatives to using Daphnia

24-25

Appendix B: Class Data Table

26

Appendix C: How to Use an Experimental Design Planner

27



Teachers, we would appreciate your feedback. Please complete our brief, online Environmental Health Science Activity Evaluation Survey after you implement these lessons in your classroom.

The survey is available online at: www.surveymonkey.com/s.asp?u=502132677711

Pre/Post Test

Name ___________________________________ Class ______

Base your answers to these questions on the student lab report below.

O


100
ur group used a Daphnia bioassay to investigate what effect Toxicant X has on living organisms. We filled 6 test tubes with solutions that had different concentrations of Toxicant X. Next we added 10 Daphnia to each test tube. After 10 minutes, we counted the number of Daphnia that died and calculated the percent of Daphnia mortality in each tube. This graph shows the results of our experiment.

D
80
aphnia Mortality


A
60
fter 10 Minutes



20

40

50
(Percent)




































































































































































































































































































0 0.5 1.0 1.5 2.0

Toxicant X Solution Concentration (Percent)



  1. The bioassay was used to determine

1. What kind of Daphnia can survive exposure to Toxicant X.

2. What concentrations of Toxicant X are harmful to Daphnia.

3. What kind of Toxicant X is harmful to Daphnia.

4. What effect the Daphnia have on the Toxicant X concentration.




  1. What is the best title for this graph?

1. The Effect of Daphnia Mortality on Toxicant X Concentration

2. The Effect of Toxicant X Concentration on Daphnia Mortality

3. Toxicant Mortality X versus. Daphnia Concentration

4. Daphnia Percent vsersus Toxicant X Percent



  1. Toxicologists call this type of graph a

1. dose-response curve

2. toxicant-cause curve

3. lethal-dose curve

4. survival-mortality curve




  1. The Daphnia exposed to the 0% Toxicant X concentration

1. were the control for the experiment

3. all survived

2. were exposed the toxicant

4. all died





  1. What is the dependent variable in this experiment?

1. The Daphnia

2. The Toxicant X Concentration

3. The % of Daphnia that died

4. The type of toxicant Daphnia were exposed to.




  1. What is the highest concentration of Toxicant X that had no effect on Daphnia mortality?

1. 0.5% 2. 1.0% 3. 1.5% 4. 2.0%


  1. At which concentration did Toxicant X have the greatest effect on Daphnia mortality?

1. 0.5% 2. 1.0% 3. 1.5% 4. 2.0%


  1. What is the LD 50 for Toxicant X in this experiment?

1. 0.5% 2. 0.75% 3. 1.0% 4. 1.25%


  1. What six Toxicant X concentrations were Daphnia exposed to in this experiment?

1. 0%, .25%, .5%, 1%, 1.5%, 2%

2. 0%, .5%, 1%, 1.25%, 1.5%, 2%

3. 0%, 10%, 25%, 50%, 75%, 100%

4. 0%, 20%, 40%, 60%, 80%, 100%




  1. Which is the most likely explanation for the observation that some of the Daphnia in the 0% Toxicant X solution died?

1. Even low concentrations of this toxicant are hazardous.

2. Other factors, besides this toxicant, affect Daphnia survival.

3. There was an error in the design of the students’ experiment.

4. The students recorded the number, not the percentage, of the Daphnia.


Teacher Answer Key - Pre/Post Test
Name ___________________________________ Class ______

Base your answers to these questions on the student lab report below.

O


100
ur group used a Daphnia bioassay to investigate what effect Toxicant X has on living organisms. We filled 6 test tubes with solutions that had different concentrations of Toxicant X. Next we added 10 Daphnia to each test tube. After 10 minutes, we counted the number of Daphnia that died and calculated the percent of Daphnia mortality in each tube. This graph shows the results of our experiment.

D
80
aphnia Mortality


A
60
fter 10 Minutes



20

40

50
(Percent)




































































































































































































































































































0 0.5 1.0 1.5 2.0

Toxicant X Solution Concentration (Percent)




  1. The bioassay was used to determine

1. What kind of Daphnia can survive exposure to Toxicant X.

2. What concentrations of Toxicant X are harmful to Daphnia.

3. What kind of Toxicant X is harmful to Daphnia.

4. What effect the Daphnia have on the Toxicant X concentration.




  1. What is the best title for this graph?

1. The Effect of Daphnia Mortality on Toxicant X Concentration

2. The Effect of Toxicant X Concentration on Daphnia Mortality

3. Toxicant Mortality X versus Daphnia Concentration

4. Daphnia Percent versus Toxicant X Percent




  1. Toxicologists call this type of graph a

1. dose-response curve

2. toxicant-cause curve

3. lethal-dose curve

4. survival-mortality curve




  1. The Daphnia exposed to the 0% Toxicant X concentration

1. were the control for the experiment

3. all survived

2. were exposed the toxicant

4. all died





  1. What is the dependent variable in this experiment?

1. The Daphnia

2. The Toxicant X Concentration

3. The % of Daphnia that died

4. The type of toxicant Daphnia were exposed to.




  1. What is the highest concentration of Toxicant X that had no effect on Daphnia mortality?

1. 0.5% 2. 1.0% 3. 1.5% 4. 2.0%


  1. At which concentration did Toxicant X have the greatest effect on Daphnia mortality?

1. 0.5% 2. 1.0% 3. 1.5% 4. 2.0%


  1. What is the LD 50 for Toxicant X in this experiment?

1. 0.5% 2. 0.75% 3. 1.0% 4. 1.25%


  1. What six Toxicant X concentrations were Daphnia exposed to in this experiment?

1. 0%, .25%, .5%, 1%, 1.5%, 2%

2. 0%, .5%, 1%, 1.25%, 1.5%, 2%

3. 0%, 10%, 25%, 50%, 75%, 100%

4. 0%, 20%, 40%, 60%, 80%, 100%




  1. Which is the most likely explanation for the observation that some of the Daphnia in the 0% Toxicant X solution died?

1. Even low concentrations of this toxicant are hazardous.

2. Other factors, besides this toxicant, affect Daphnia survival.

3. There was an error in the design of the students’ experiment.

4. The students recorded the number, not the percentage, of the Daphnia.


Learning Context
Subject Areas: Biology and Environmental Science
Overall Purpose:

  • To use bioassay investigations to develop students’ understanding of the effects of chemical concentration on survival of living organisms

  • Make the connection between the survival of simple organisms and human survival

  • To understand the role that model organisms play in informing humans about the effects of toxicants


Learning Objectives: Students will…

  • Develop a hypothesis about the relationship between toxicant concentration and effect on living organisms

  • Create toxicant solutions of various concentrations

  • Perform bioassay experiments using toxicant solutions

  • Record experimental data in a data table

  • Graph experimental data

  • Draw conclusions based on experimental data and their hypothesis

  • Determine the LD50 for toxicants

  • Consider the implications of their research on human health


Prerequisite knowledge and skills:

  • Measure volume in mL

  • Record data in a data table

  • Graph data

  • Design a controlled experiment



Teacher Background Information
A bioassay is a procedure that uses living organisms to determine the toxicity of a chemical. In a bioassay living organisms are exposed to different concentrations of a chemical that might be a toxicant (harmful chemical). Observations of the effects on the organisms’ behavior and survival allow researchers to determine if, or at what concentration, a chemical has harmful effects.
The bioassay protocol introduced in this learning experience is a useful method for allowing students to observe the effects of slight environmental changes in simple organisms. Daphnia are commonly used in bioassays but other aquatic organisms such as duckweed, elodea, blackworms, and planaria may be substituted.
This learning experience includes two parts. In Part 1, students are introduced to the bioassay protocol by testing the effect of various salt concentrations on Daphnia. In Part 2, students apply what they learned to conduct a bioassay to investigate the effects of another toxicant on Daphnia. There are two versions of Part 2: a guided version and an inquiry version. Teachers may select the version most appropriate for their students.
In some cases the Daphnia will die due to the concentrations of salt or other toxicants. If you and or your students prefer not to utilize Daphnia but still wish to conduct bioassays, other simple aquatic organisms such as duckweed, elodea, blackworms, and planaria could be substituted. You may also wish to have your students compare the effect of the same toxicant on different model organisms. Appendix A provides sample instructions for setting up bioassays with other model organisms.
Students will be asked to graph their data to produce what toxicologists call a “dose-response curve.” They use their graph to determine the LD50 for the toxicant. LD50 is the abbreviation for Lethal Dose, 50%. This is the concentration of a toxicant that will kill 50% of the population exposed to the toxicant. In conducting a bioassay using a variety of concentrations of one particular toxicant, students will be able to determine directly, or through extrapolation, which concentration will result in the death of 50 % of the tested population
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