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Natural Selection Lab: Brine Shrimp
Transcript of Natural Selection Lab: Brine Shrimp
and the effect of pH on hatch
viability of brine shrimp
Does pH affect the hatching viability of brine shrimp?
adhesiveness of tape
1. Prepare 5 beakers of 1.5 % salinity.
2. Label 5 beakers and 5 petri dishes: 4, 5.5, 7, 8, and 9. Place a piece of 1.5 cm of tape on the bottom in each petri dish.
3. Use a paintbrush to collect 20 eggs and stick the eggs to the tape in each of the five petri dishes.
4. Calibrate pH meter with stock solutions.
5. Titrate the solutions in the beakers labeled "4" and "5.5" to the pH on their individual labels with a 0.5 molar solution of sulfuric acid solution.
6. Do not titrate the beaker labeled “7.”
7. Titrate the solutions in beaker "8" and "9" to the pH on their individual labels with a 0.2 molar solution of sodium hydroxide solution using a glass pipet.
8. Pour the solution in each beaker into its corresponding petri dish. Allow the dishes to sit at room temperature undisturbed for 24 hours.
If the hatch viability of brine shrimp is affected by environmental conditions, such as pH, then the hatch viability will be greatest at a pH of 8 because this is close to the pH of their most favorable environment, brackish water.
salinity of 1.5% in each petri dish
volume of solution
each dish (presumably) exposed to identical conditions
Experimental set up:
Variables Observed in this Experiment
Independent Variable: pH
Dependent Variable: Hatch Viability
Hatch Viability Calculation:
dish 1 (4.18): (0+0+4+3)/(20)=0.350 35.0%
dish 2 (5.52): (0+0+4+0)/(20)=0.200 20.0%
dish 3 (7.10): (0+0+8+0)/(20)=0.400 40.0%
dish 4 (8.07): (3+0+4+0)/(21)=0.333 33.3%
dish 5 (9.05): (1+0+4+1)/(20)=0.300 30.0%
Highest Viability (40%)
1. Using a stereomicroscope, count and remove the swimming brine shrimp with a pipet. Record this number under “24 hours.”
2. Count and remove the dead brine shrimp with a pipet. Record this number under “24 hours.”
3. Count the number of unhatched brine shrimp eggs and record this number under “24 hours.”
4. Repeat steps 1-3 for each of the petri dishes.
1. Using a stereomicroscope, count and remove the swimming brine shrimp with a pipet. Record this number under “48 hours.”
2. Count and remove the dead brine shrimp with a pipet. Record this number under “48 hours.”
3. Count the number of unhatched brine shrimp eggs and record this number under “48 hours.”
4. Repeat steps 1-3 for each of the petri dishes.
Sulfuric acid (corrosive, irritant)
skin contact -> burns ( itching, scaling, reddening, blistering)
eye contact -> irritation (redness, watering, itching)
inhalation -> damage respiratory tract
inhalation -> cough, sore throat, burning sensation, shortness of breath
skin contact -> burns (red, blisters)
eye contact -> burns (Redness, blurred vision)
ingestion -> abdominal pain, burning mouth and throat, sensation in the throat and chest, nausea, vomiting
brine shrimp eggs
double sided tape
200 ml dechlorinated water
10 petri dishes
3 grams sodium chloride
0.5 molar sulfuric acid
0.2 molar sodium hydroxide
calibrated pH meter
pH stock solutions (pH of 3,4,5,8,9,10)
5 microscope slides
Predicted a bell curve-relationship of pH and viability with 8 as the highest pH
pH of 7 had the highest hatch viability
4.18 unexpected as the second highest, possible explanation:
counted both the number of swimming and dead brine shrimp
pH of 4.18 had 3 dead
Time on microscope->heat and light
Our hypothesis implies that brine shrimp should remain in cyst form in unfavorable conditions (i.e. pH of 4)
Possible sources of error:
Small sample size
1 group-heavily influenced by random error
only about 20 brine shrimp eggs/pH
no repetition of lab
Temperature was not controlled
ideal temp: 80°F - 82°F
perhaps higher temperature for brine shrimp in pH of 4.18 (explains higher hatch viability)
Light was not controlled
less light = lower hatch rate
perhaps more light for the brine shrimp in pH of 4.18 (explains higher hatch viability)
pH meters were problematic
Adhesiveness of tape was variable in each solution
some eggs were observed floating on the surface in each petri dish, only submerged eggs will hatch
Why does the pH of 4.18 have a higher hatch viability than the pH of 5.52?
pH of 4.18 represents acid rain - less favorable conditions expected to have lower hatch viability
pH of 5.52 represents rain water
more natural environment than acid rain
Did the sulfuric acid dissolve any of the brine shrimp?
acid may have corroded brine shrimp before counted – hatch viability may be lower than recorded
Are the eggs placed in the dishes from the same parents?
variability in hatch viability - are some naturally better in some environments?
How would pH affect overall maturing time/maximum length?
Let's dive deeper...
A presentation by Gabe, Gabby, and Sarah
Experimental Control group: pH of 7.00 +/- 0.2
Hypothesis was incorrect
Highest to lowest hatch viability:
1. pH of 7.10 (40.0%)
2. pH of 4.18 (35.0%) <-- not ideal environment
3. pH of 8.07 (33.3%) <-- predicted as highest
4. pH of 9.05 (30.0%)
5. pH of 5.52 (20.0%)
Microscope or weather increased heat and light exposure unevenly between dishes
Crux of Natural Selection: Differential Reproductive Success
offspring that hatch in one environment pass their more adept genes on to the next gen. in population
Diff. Rep. Succ. shows how populations can change based on the genes that pass down from generation to generation
Significant variables not controlled:
Heat (higher temps yields higher viability)
Light (necessary for hatching)
No major methodology problems
Changes for next time:
Try using tweezers - paintbrushes are sloppy
Define hatch viability as a group beforehand
Stickier tape - adhesiveness affects hatching
Smaller dish size
Microscope / Weather -introduced variables
Further proof for natural selection
Used to test ecotoxicity in agriculture
Test for warfare agents in liquid food
Ballast water testing irradication