LD-50 Lab
Pre Lab
- Dependent Variables: germination rate of radish seeds.
- Independent Variables: concentration of chemical (salt) in solution.
- Hypothesis: If there is more salt in the solution then there will be less germination and root length because the salt either kills the plant or inhibits its growth.
Problem
Does the amount of concentration of NaCl have any effect on the germination and growth of a plant?
Hypothesis
If there is more salt in the solution then there will be less germination and root length because the salt either kills the plant or inhibits its growth.
Experiment Parts
Independent Variable: Concentration of chemical (NaCl) in solution.
Dependent Variable: Germination rate of radish seeds, radical length.
Control Variables: The same type of petri dishes and paper towels, water from the same source.
Control Group: Petri dish #1 which contained no NaCl.
Experimental Groups: The other 5 petri dishes that contained different NaCl concentrations.
Dependent Variable: Germination rate of radish seeds, radical length.
Control Variables: The same type of petri dishes and paper towels, water from the same source.
Control Group: Petri dish #1 which contained no NaCl.
Experimental Groups: The other 5 petri dishes that contained different NaCl concentrations.
Materials
- 6 petri dishes
- 60 seeds
- 12 paper towels
- Concentrated salt water solution
- Water
- Graduated cylinders
- Test tubes
Procedure
- Use the graduated cylinders and test tubes to prepare the various concentrations of NaCl-Water solutions.
- Label all six petri dishes with your group number, and the dish number.
- Fold together two paper towels and cut it to where it fits inside the petri dish.
- Carefully pour the chemical solutions onto the napkins. (Make sure you match the solutions with concentration percentages of the dish).
- Count out 10 seeds and place them on the moist paper towel in the petri dish.
- Repeat steps 3-5 for other dishes.
- Place the seed dishes in a stack, lying flat with the seeds up and put them in a spot designated by your teacher.
- After 3-4 days check on your dishes.
- Count and calculate the percentage of seeds germinated for each dish.
- Measure the length of each radical in millimeters. Make sure you are measuring just the root not the sprout.
- Calculate the mean radical length for each salt solution by adding the total radical lengths and dividing by the total number of seeds that germinated. DO NOT include data from seeds that did not germinate.
Observations
The seeds that were in the control and the 3 dishes with low NaCl concentration germinated excellently and can be seen below in the pictures. The percent germinated ranged from 90% to 100%. The other two dishes, however, which had high NaCl concentrations had very little to no germination happening. Our groups data was the most successful out of our class because we seemed to have the most seeds germinated and the longest radical growth despite the fact that we drowned our seeds and paper towels for the first 3 petri dishes just like most of the groups in the class; however, there were a couple of groups that had results similar to ours.
Pictures
Data Table and Graphs
Analysis and Conclusion
1. What appears to be the LD-50 for salt for radish seeds? Support your answer with data.
The LD-50 for salt for radish seeds appears to be 10.00 mL. It is clearly visible that in the petri dish that contained this amount of concentration and the ones right after it more than half or nearly all of the seeds did not germinate. Unlike in the dishes that contianed less NaCl concentration and had 90%-100% seeds germinated.
2. Is your radical data supported by your germination data? Support your answer with data.
The radical data is supported by the germination data because in petri dish number 1, 2, and 4 the percent germinated was 90 and the radical length ranged from .3 to 5.7 cm. Group 3 had an even higher percentage germinated at 100 and they had the longest radical length ranging from 1 to 7.1 cm. Compared to petri dish number 5 which had only 40 percent of seeds germinated and 10.00 mL of NaCl solution and where the mean radical length was only 3.25 mm.
The LD-50 for salt for radish seeds appears to be 10.00 mL. It is clearly visible that in the petri dish that contained this amount of concentration and the ones right after it more than half or nearly all of the seeds did not germinate. Unlike in the dishes that contianed less NaCl concentration and had 90%-100% seeds germinated.
2. Is your radical data supported by your germination data? Support your answer with data.
The radical data is supported by the germination data because in petri dish number 1, 2, and 4 the percent germinated was 90 and the radical length ranged from .3 to 5.7 cm. Group 3 had an even higher percentage germinated at 100 and they had the longest radical length ranging from 1 to 7.1 cm. Compared to petri dish number 5 which had only 40 percent of seeds germinated and 10.00 mL of NaCl solution and where the mean radical length was only 3.25 mm.
General Analysis and Conclusion
Hypothesis Evaluation: In the hypothesis it was predicted that if there is more salt in the solution then there will be less germination and root length which turned out to be completely accurate. The control and the dishes with little NaCl present experienced higher percentages of germination compared to the dishes that had more than 10.00 mL of NaCl.
Accuracy of Results: For the most part, the results were pretty accurate with the exception of the first 3 groups where there was too much water and the seeds and paper towels were soaked instead of just moist. That could have swayed our results and allowed for so much growth and germination in those 3 groups because more water made the NaCl concentration even smaller compared to the other groups where the experiment was conducted correctly. This experiment could have been done better if we knew exactly how much water was needed to be put inside each petri dish. Also seeds don't always germinate generally only around 80 percent of seeds germinate out of a packet of seeds so there could have just been some seeds that didn't germinate not due to the salt. So to eliminate that variable many tests would have to be taken with similar results.
Application: From this lab I learned that LD-50 or Lethal Dose 50 is the amount of a substance required to kill fifty percent of a population. I also learned that this method is used to test out new drugs and their toxicity before they can be used by humans. I have learned from this lab that it can also be a very good indicator of in what doses something can be tolerated. In our lab our ranges were pretty far apart but even with the doses being very different there was a clear defining point of what was okay for the plant and what was harmful. If we took it into more detail and did more detailed measurements of the salt concentration and varied it smaller then I believe this method would give very accurate results.
Real Life Example: The article "Goodbye to LD50" talks about how LD50 tests are not effective and do not portray valid and useful information that is beneficial to humans. The author found out from various biotech and pharmaceutical companies that they actually used other methods to find out the starting dose in humans, the organ that was affected, and for predicting acute overdose situations, the LD50 method was very much avoided. While reading through the comments below the article I stumbled upon different opinions regarding the LD50 tests. Some people believe that LD50 is crucial for determining the levels of toxicity of the drug and that mice are the perfect species to test it on while others believe that mice do not have the same physiology as humans therefore any results conducted from the LD50 experiment would be inaccurate when relating to humans. In some ways, I believe, this test helps and in others it does not. In this lab I observed that the petri dishes that contained more NaCl had very little germination and the ones that contained a little amount of NaCl experienced a lot of growth. Therefore it can be concluded that the LD50 test is actually somewhat useful when trying to determine the toxicity of a chemical; however, I also agree that testing the chemicals on mice does not produce the most accurate results because of the differences in physiology.
Zielinska, Edyta. "Goodbye to LD50?." The Scientist. The Scientist, 9 Jan. 2008. Web. 26 Mar. 2013. <http://www.the-scientist.com/?articles.view/articleNo/25905/title/Goodbye-to-LD50-/>.
Accuracy of Results: For the most part, the results were pretty accurate with the exception of the first 3 groups where there was too much water and the seeds and paper towels were soaked instead of just moist. That could have swayed our results and allowed for so much growth and germination in those 3 groups because more water made the NaCl concentration even smaller compared to the other groups where the experiment was conducted correctly. This experiment could have been done better if we knew exactly how much water was needed to be put inside each petri dish. Also seeds don't always germinate generally only around 80 percent of seeds germinate out of a packet of seeds so there could have just been some seeds that didn't germinate not due to the salt. So to eliminate that variable many tests would have to be taken with similar results.
Application: From this lab I learned that LD-50 or Lethal Dose 50 is the amount of a substance required to kill fifty percent of a population. I also learned that this method is used to test out new drugs and their toxicity before they can be used by humans. I have learned from this lab that it can also be a very good indicator of in what doses something can be tolerated. In our lab our ranges were pretty far apart but even with the doses being very different there was a clear defining point of what was okay for the plant and what was harmful. If we took it into more detail and did more detailed measurements of the salt concentration and varied it smaller then I believe this method would give very accurate results.
Real Life Example: The article "Goodbye to LD50" talks about how LD50 tests are not effective and do not portray valid and useful information that is beneficial to humans. The author found out from various biotech and pharmaceutical companies that they actually used other methods to find out the starting dose in humans, the organ that was affected, and for predicting acute overdose situations, the LD50 method was very much avoided. While reading through the comments below the article I stumbled upon different opinions regarding the LD50 tests. Some people believe that LD50 is crucial for determining the levels of toxicity of the drug and that mice are the perfect species to test it on while others believe that mice do not have the same physiology as humans therefore any results conducted from the LD50 experiment would be inaccurate when relating to humans. In some ways, I believe, this test helps and in others it does not. In this lab I observed that the petri dishes that contained more NaCl had very little germination and the ones that contained a little amount of NaCl experienced a lot of growth. Therefore it can be concluded that the LD50 test is actually somewhat useful when trying to determine the toxicity of a chemical; however, I also agree that testing the chemicals on mice does not produce the most accurate results because of the differences in physiology.
Zielinska, Edyta. "Goodbye to LD50?." The Scientist. The Scientist, 9 Jan. 2008. Web. 26 Mar. 2013. <http://www.the-scientist.com/?articles.view/articleNo/25905/title/Goodbye-to-LD50-/>.