Dependant variables:
These are the variables which will be measured. In this experiment there is only one dependant variable. This is the amount of brine shrimps that hatch per day in each test. Each hatched shrimp shall be removed and placed into a separate salt solution, so that they are not counted several times.
Controlled Variables:
These are the variables which we will try to maintain to the best of our ability. There are several controlled variables in this experiment:
- The temperature in each of the experiments must be maintained. The water bath tests will be maintained at their correct temperatures by an electronic thermostat (20,25 and 30°C. This needs to be programmed to the correct temperature. The test in the fridge will also be kept at the same temperature by an onboard thermostat(4°C). The test that is going to in the biology lab will only be maintained to a range of degrees (17°C). This is because the room operates a thermostat which has a 2-3º variation range. If the ambient temperature drops below 2-3º of a set level, the heating comes on, and vice versa.
- The number of brine shrimp added to each test beaker must also be the same to the best of our ability. The cysts are very small and some variation in numbers is expected. This is not a problem as long as the number of shrimps in each beaker is near to being equal. There should be a 5 cysts degree of error across all tests.
Reliability:
Each experiment shall be carried out 4 times to get a broader spectrum of results. This will allow for any mistakes in counting or during hatching of the shrimps. This can then allow for an average value to be taken.
Ethics:
This experiment requires the use of live animals, their safety is very important. Great care must be taken during the handling of these creatures, pipettes are being used in order to transport them form beaker to beaker and the cysts must be used carefully. Any excess cysts must be returned to their container for use in the future as they deserve the chance to develop at some stage. Developed shrimps must be disposed of appropriately after the experiment by being placed into a pond or other saltwater environment.
Apparatus:
- 5 small beakers
- 1 large beaker
- 3x water baths set at 20, 25 and 30°C respectively.
- Fridge set at 4°C
- Thermostat controlled biology laboratory at 17°C
- Pipette
- Brine water (salt solution)
- Brine shrimp cysts (40 for each test beaker)
- Forceps
- White paper, graph paper.
- Marker pen (water resistant)
- Magnifying lens.
Method:
- Place 2g of sea salt into a beaker for the salt solution. Add 100cm3 of de-chlorinated water and stir.
- Label the beakers with the conditions they are going to be exposed to.
- Place some cysts onto a piece of plain white paper.
- Wet some graph paper that has been cut to a smaller size and count 40 cysts onto this graph paper using forceps.
- Place the graph paper into the salt water and leave for 20 seconds.
- Shake the graph paper inside the salt to remove all of the cysts.
- Repeat steps 3-6 for other beakers.
- Place the corresponding beaker into each environment. Leave for 1 week.
- Count how many cysts have hatched and remove hatched shrimp into a separate salt water filled beaker. Count how many shrimp were removed from each beaker.
- At the end of the week count all hatched shrimp and place into a separate large beaker containing salt solution.
- Repeat 4 times.
Results:
Discussion:
The results show that there is an optimum temperature region at which to grow brine shrimp.
Temperatures in the region of 25°C produced the most brine shrimp over each week and the average value is also above the other conditions. At 4°C it was simply too cold for the brine shrimp to hatch, with a sum total of no shrimp hatching in any of the 5 tests.
The 17°C results were very low with a maximum of 2 shrimp in the most successful trial, trial 2. This supports my hypothesis of “This higher temperature is what I believe to be the most suitable temperature for the shrimps. This is because at lower temperatures, the hatching process is delayed and the percentage of eggs hatched is reduced.” However, I predicted that the 30°C experiment would be the most successful, but it was not, the slightly lower temperature of 25°C was the most successful. I was also incorrect in saying that there would be very little difference between 25 and 30°C. Although the two temperatures are very close to each other, the optimum temperature must obviously be nearer to the 25°C level, as this had a much more profound impact upon the hatching of the shrimp. The 30°C experiment did not have the effect that I predicted. I believe that this was caused by the temperature being too close to the threshold in which the shrimp cannot survive at around 35°C. The 25°C trial was however far enough away from that threshold to have a larger impact upon the hatching of the shrimp.
The first trial was not as successful as hoped due to alterations in the concentration of all the solutions over the week. In the warmer temperatures, the water begun to evaporate and therefore increased the salinity of the remaining solution. After a week of increasing salinity the cysts either did not hatch or were poisoned by the salinity of the solution. All other trials were carried out with cling film covering the beakers containing the shrimp, so that any evaporated water condenses on the cling film and returns to the beaker.
There was also an issue of the salt leaving the solution and forming salt crystals at the base of the beaker in the 4°C experiments. this affected salinity by reducing the salt content in solution. This was evident in all trials with cling film over the beakers, but not to the extent of the 4°C experiments which may have contributed to the increased volume of shrimp hatching.
During trial number 3 for the 35°C experiment, there was an incident concerning the water bath being turned up to a higher temperature. This essentially killed the shrimp off and resulted in none surviving for the whole week. There was another incident involving the shrimp being knocked over inside the water bath resulting in void results as no shrimp remained in the beaker. This occurred on the trial 4, 17°C experiment.
In order to prevent this from occurring in any future experiments, the water bath should contain a grid which can hold the beakers in place and prevent them from floating around. The water bath adjustment is easy to make and is unavoidable if left in a biology lab with students coming in and out all day. There is also no way of preventing the salt leaving the solution in the colder temperatures, without warming the solution up, affecting the results.
