hatch-a-cyst teacher guide - geneticsteach.genetics.utah.edu/content/gsl/pdfs/hatcha... ·...

BACKGROUND

Brine Shrimp (Artemia franciscana) are tiny crustaceans that live in saltwater environments such as Great Salt Lake.

When environmental conditions are good, females release actively developing embryos. But in stressful environmental conditions females release dormant cysts. Inside the cysts, the embryos can remain arrested in development for years while the surrounding shell protects them from the elements. When conditions improve, the embryo resumes development, and the life cycle continues. As is the case with any ecosystem, abiotic factors such as light and temperature shape the environment of brine shrimp, determining when they hatch and to what extent these organisms thrive.

In addition to being a vital part of Great Salt Lake's ecosystem, brine shrimp have an economic importance as well. Each fall, brine shrimp fishermen collect and sell cysts, an industry that generates about $40-60 million dollars each year. The cysts can be stored dry on shelves until needed. Once hydrated, the embryos inside hatch quickly and the young nauplii are fed to fish and shellfish that are raised for human consumption.

What are the ideal conditions for hatching brine shrimp? Design an experiment to test how a particular abiotic factor affects a population of brine shrimp. Pool your results with the class to determine the overall best environment for hatching these resilient and hardy organisms.

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HATCH-A-CYST Teacher Guide

Teach.Genetics.utah.eduGENETIC SCIENCE LEARNING CENTER

© 2011 University of Utah 1

Funding for this module was provided in part by Westminster College and by a grant awarded under the Workforce Innovation in Regional Economic Development (WIRED) Initiative as implemented by the U.S. Employment and Training Administration.

FUNDING

The following worksheets are a step-by-step scaffold for designing an experiment. Students may also use the worksheets as a lab write-up.

BEGIN

1. List the abiotic factors brine shrimp are likely to encounter in environments such as

Great Salt Lake:

You may want to generate this list as a class. Ideas include:• Extreme Salinity• Light• UV Exposure• Fluctuations in pH• Heat

• Cold• Oxygen Levels• Pollution (from runoff and wastewater treatment)• Boats• Brine Shrimp Fishermen

2. Which of the factors listed above can you change in the laboratory?

This step is helpful in prompting students to think about what is testable and which materials they might have available.

3. Determine which abiotic factor you will test:

I will change (the variable):

Ideally each testable abiotic factor identified above will be tested by at least one lab group. You may wish to assign this, or let students choose their own with minimal overlap.

I will measure: the percentage of cysts that hatch (# of hatched cysts / total # of cysts)

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DESIGN AN EXPERIMENTThe purpose here is to ensure that a control group is part of each experiment and to give students some experience working with the brine shrimp before designing their experiments.

SET UP A CONTROLSet up a group of brine shrimp cysts for which all abiotic factors will remain constant (or the same). This is your control group. Comparing your experimental group against your control group will tell you if the abiotic factor you change has any effect.

1. You will need the following materials:

☐ Small Petri dish ☐ Paper towel ☐ Scissors ☐ Pipet or dropper ☐ Microscope or hand lens ☐ 10 mL of 3% salt solution ☐ Beaker of hydrated brine shrimp cysts

2. Cut off a piece of the paper towel and fold it to fit in the bottom of the Petri dish. You may trim the corners to help it fit. Label the lid of the dish with the following: Your name, “Control”.

3. Gently swirl the beaker of hydrated brine shrimp cysts. Use a pipet or dropper to collect a sample of cysts from the bottom of the beaker (you do not want the empty cyst cases that are floating on the top).

4. Drop your cyst sample evenly over the paper towel-lined Petri dish by gently squeezing your pipet or dropper. Aim for 30 - 50 cysts per paper towel.

5. Use the pipet or dropper to further hydrate the paper towel with 3% salt solution. Be sure the paper towel is completely wet, but not so wet that the cysts can float away.

6. Using a hand lens or microscope, count the number of brine shrimp cysts present in your Petri dish and record the number on the lid.

7. Place your dish in the designated area of the classroom.

You will compare how many brine shrimp cysts hatch in this group to the number that hatch in the experiment you design.

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SET UP TEST GROUPS

Hypothesis1. Changing the abiotic factor of ____________________ will affect the hatch rate of brine

shrimp cysts.

If your students have prior knowledge of brine shrimp and their ideal environment, you may wish to have them create a hypothesis that is more specific to the abiotic factor they are testing.

2. List three things that will remain constant in your experiment: A. B. C.

Experimental Design 1. Materials I will need:

2. How I will set up the experiment: (*the cysts will hatch in 1 - 2 days)

Prompts for students:• Think about testing a gradient of your abiotic factor • Ensure that the factors listed above remain constant• Be sure to count cysts before they are hatched• Set up your experiment so it is easy to count hatched nauplii • Is time a factor?

3. Data I will need to record:

Prompts for students:• What will you record at the beginning of the experiment?• What will you record at the end of the experiment?

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Others should be able to follow your design without needing to ask you any questions.

NOTE

4. How I will record and display my data: (Include a chart, table, graph, picture or some other way to record your data while your experiment is underway.)

Students will record their data here. Prompt them to include data for the control group as well.

Obtain permission from your teacher to begin and set up your test groups.

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As cysts hatch they swell with water and crack as the embryos inside begin to grow. When the nauplii first emerge they are still wrapped in hatching membranes. Fully hatched nauplii are pale yellow and swim with jerky movements. In ideal conditions, cysts hatch in 1 - 2 days.

TIP

RESULTS

Title of Graph: ________________________________________________

CONCLUSION

What did you learn about the abiotic factor you tested and its effect on brine shrimp hatch rate?Prompt students to explain this as they would to a friend (rather than restating their hypothesis). Ex: "Brine Shrimp hatch in temperatures ranging from 25° C - 32° C". Pool the conclusions from all lab groups to determine the best environment for hatching brine shrimp.

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TEACHER RESOURCE

Abiotic factors to test on brine shrimp cyst hatch rate

Abiotic Factor What to Use Background

Salinity Create several concentrations of salt solution by dissolving different amounts of Instant Ocean™ or non-iodized salt in tap or deionized water. Calculate percent salinity in grams per 100 mL.

Brine shrimp cysts will hatch in salinities ranging from 3%-20%.The optimal salinity for hatching is around 9%, however, the algae that brine shrimp eat need a salinity of about 13%. Conditions in the Great Salt Lake support this difference: when spring runoff decreases the salinity of the lake temporarily, the brine shrimp hatch rate increases. As salinity levels decrease, algal growth increases.

Light Use aluminum foil, fabrics of different opacity or different locations around the room to vary the amount of light brine shrimp cysts receive.

Newly hatched nauplii are attracted to light and will swim toward it.

UV Exposure A UV light box can provide direct exposure. If you don't have access to a UV light box, the "sterilize" function on many goggle cabinets uses UV light.

At 4,200 feet in elevation, brine shrimp of the Great Salt Lake receive ultraviolet light levels that are about 15% higher than at sea level.

pH Household chemicals such as bleach, vinegar, lemon juice and baking soda can be used to alter the pH of the water in which you hatch your brine shrimp.

Bleach solution decapsulates brine shrimp cysts. Decapsulated embryos will sink to the bottom of the hatching container. Hatcheries sometimes use bleach solution to separate the empty cysts from those that contain embryos.

Temperature An incubator, heat lamp, refrigerator and freezer can be used to alter the temperature where brine shrimp hatch.

Dehydrated cysts will tolerate extreme heat and freezing temperatures with embryos intact. They will hatch in temperatures ranging from 25o C - 32o C.

Oxygen Levels Sealing containers and using a small aquarium pump and flexible tubing are two ways to change the level of oxygen for hatching cysts.

Cysts will not hatch in extremely anoxic conditions.

Pollution Examples include yard care chemicals, insect repellents, insecticides, auto care chemicals and ethanol.

Urge students to think about common household pollutants that might run off into Great Salt Lake and the impact the surrounding areas might have on the lake's ecology.

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hatch-a-cyst teacher guide - geneticsteach.genetics.utah.edu/content/gsl/pdfs/hatcha... ·...

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