24 A Closer Look at Arthropods

CHAPTER 24
MATERIALS
• clear plastic cups
• 100-mL graduated
cylinder
• 400 mL sea salt solution
• 0.1 g brine shrimp eggs
• plastic spoon
• balance
• clear plastic wrap
• aluminum foil
• clear plastic bottles
with lids
• vinegar
• baking soda
• pH duo-test paper
• 2 eyedroppers
• 10 petri dishes
• hand lens or dissecting
microscope
• lamp
PROCESS SKILLS
• Designing Experiments
• Collecting Data
• Analyzing
• Predicting
DESIGN YOUR OWN INVESTIGATION
Hatching Brine Shrimp
Brine shrimp are small arthropods found in oceans, salt lakes, estuaries, and tidal
ponds. Brine shrimp are used primarily for fish food, especially on fish farms where
natural food sources are unavailable. Their eggs can be harvested and hatched
under controlled conditions by biologists working in an aquaculture facility. In this
investigation, you will design an experiment to determine the best conditions for
hatching brine shrimp eggs.
PROBLEM What are the best conditions for hatching brine shrimp eggs?
PROCEDURE
1. Choose one factor to investigate. Some factors to consider are the presence or
absence of light, aeration (open container versus air-tight container), and pH (6–8).
Make a hypothesis about that factor, and design an experiment to test your
hypothesis. Have your teacher approve your design.
2. The conditions of the hatching (temperature, pH, light conditions, and so on) will
depend upon your independent variable. If you are testing pH, use vinegar to
adjust the pH of the sea salt solution to pH 6.0 or baking soda to adjust the pH
to 8.0 as measured with the pH test paper.
3. Determine the number of cups of brine shrimp needed based on your
experimental design. Be sure to include a control. Hatch the brine shrimp eggs
by filling each cup with 200 mL sea salt solution and 0.1 g brine shrimp eggs.
Cover the cups with plastic wrap or aluminum foil depending upon your
experiment. If you are testing aeration, use bottles with lids instead of cups.
4. Once you have set up your cups or bottles,
remove 5 mL from each with an eyedropper
and place each volume in a separate clean step 4
petri dish.
5. Examine each dish with a hand lens or
microscope. Count the number of eggs
and the number of hatched brine shrimp.
Note these numbers.
6. Repeat steps 4 and 5 each day for five
days and note the numbers of hatched
shrimp and eggs each day.
ANALYZE AND CONCLUDE
1. Analyze Graph the data with the number of shrimp hatching or number
of shrimp hatching rate (shrimp hatching divided by number of eggs) on the
y-axis and the days on the x-axis.
2. Analyze On what day did you observe the most shrimp hatching? Was this day
consistent with the findings of other members of your group? List possible
reasons for inconsistent results.
3. Experimental Design Identify possible sources of error in your experiment and
give reasons why they might have occurred.
4. Analyze How did your factor affect the hatching of brine shrimp?
5. Infer Compare your team’s result with other teams in your group. Identify
conditions that had the most positive effect on the hatching of brine shrimp.
6. Experimental Design Explain why it was important to have a control in
your experiment.
Chapter 24: A Closer Look at Arthropods 739