LD50 Lab
Problem: How does concentration of saltwater affect radish seed germination?
Hypothesis: Salt water causes a decrease in germination.
IV: concentration of salt
DV: germination
Ctrl: dish #1 (no salt)
Materials:
6 petri dishes
6 seeds
12 napkins
Water
Graduated cylinder
Concentrated Salt Water solution\
Procedure:
Hypothesis: Salt water causes a decrease in germination.
IV: concentration of salt
DV: germination
Ctrl: dish #1 (no salt)
Materials:
6 petri dishes
6 seeds
12 napkins
Water
Graduated cylinder
Concentrated Salt Water solution\
Procedure:
- Use the graduated cylinders and test tubes to prepare the various concentrations as shown below.
- Label all six petri dishes with your group number, the dish #, and a percent concentration of chemical:
- Dish #1: 0%
- Dish #2: 6.25%
- Dish #3: 12.5%
- Dish #4: 25%
- Dish #5: 50%
- Dish
#6: 100%
- Put two napkins together and cut them so that they fit into the petri dish.
- Put on the safety goggles and latex gloves. Carefully pour the chemical solutions onto the napkins, making sure to match the numbers and concentration percentages of the dish.
- Count out 10 seeds. Carefully place the seeds on the moist napkins in the petri dish.
- Repeat steps 3-5 for the other dishes.
- Place the seed dishes in a stack, lying flat with the seeds up. Put the seeds in the spot designated by your teacher.
Collecting Data and Plotting Results
You will measure the response of the radish seeds at various salt concentrations. After the seeds have germinated, count the number of seeds that germinated and measure the length of each radical (embryonic root). After recording your results, you will create two graphs (% seed germination and dose-response curve) to help you analyze the data collected.
You will measure the response of the radish seeds at various salt concentrations. After the seeds have germinated, count the number of seeds that germinated and measure the length of each radical (embryonic root). After recording your results, you will create two graphs (% seed germination and dose-response curve) to help you analyze the data collected.
- Remove the lid of the control dish. Count the number of seeds that germinated. Calculate the percentage of seeds that germinated and record in Table 2. Note: if fewer than 80% of the seeds in this control sample germinate, this indicates a problem with the experiment.
- Measure the length of the radical for each of the germinating lettuce seeds to the nearest millimeter (mm). Look carefully at each sprout to make sure you are measuring just the root, not the shoot as well. In the picture below, you would measure just the part between the two arrows, not the shoot and cotyledons to the left.
- Repeat steps 1-2 for each petri dish.
- For each treatment, calculate the mean radical length for each salt solution. Add the total radical lengths for each salt solution and divide by the total number of seeds that germinated. Do not include data from seeds that did not germinate. Record data in column labeled, “Mean Radicle Length (mm).”
- Make a line graph from the data collected to show a dose-response curve. The horizontal axis should be for the independent variable, dose (concentration of salt solutions). The vertical axis should be for the dependent variable, response (mean radical length). Remember to give the graph a title.To help you answer “Did the radical length increase or decrease in length as compared to the control?” subtract the mean radical length of each treatment from the mean radical length of the control. Record your answers in the column, “Difference in Radicle Length” on the data table.
- Make a line graph to show the percentage of seeds that germinated for each salt solution.
Observations
There were seed coats on at least three pods and the sprouts were green. There was a notable odor when we opened the case.
Specific Conclusions
1. What appears to be the LD 50 for salt for radish seeds? Support your answer with data.
The LD50, the level at which 50% of seeds are affected, is around 2.5 mg/L concentration of salt, close to 20% concentration. The second line graph shows the point where 50% of seeds fail to germinate between 1.5 and 3 mg/L.
2. Is your radicle data supported by your germination data? Support your answer with data.
Yes, because the lower the concentration of salt, the longer the average radicle. This is shown in the first line graph. As the dose decreased, the amount of germinated seeds increased as did the average radicle length.
The LD50, the level at which 50% of seeds are affected, is around 2.5 mg/L concentration of salt, close to 20% concentration. The second line graph shows the point where 50% of seeds fail to germinate between 1.5 and 3 mg/L.
2. Is your radicle data supported by your germination data? Support your answer with data.
Yes, because the lower the concentration of salt, the longer the average radicle. This is shown in the first line graph. As the dose decreased, the amount of germinated seeds increased as did the average radicle length.
General Conclusions
Evaluation of Hypothesis: I predicted that the salt would make it more difficult for the seeds to germinate. As the data shows, higher salt concentrations resulted in fewer germinated seeds. My hypothesis is valid.
Accuracy: Some measurements may be imprecise, as it was difficult to straighten out the radicles against the ruler. Also, there was minor confusion in the recording of data when it came to percentages, such as the petri dishes being labeled incorrectly at first.
Real-Life Application: Knowing the LD50 of a substance can help to determine just how dangerous it is to ingest. In a case of poisoning recently, a man poisoned his girlfriend with Visine eye drops (Wired), the LD50 of which was found to be 345 kg/mg. People assume poisoning via Visine is irritating but harmless because of the movie "Wedding Crashers," but in actuality it's poisonous enough to kill. When people don't grasp the toxicity of substances, they can endanger others.
Works Cited
Blum, Deborah. "Just an (Eye) Drop of Poison." Wired.com. Conde Nast Digital, 23 Mar. 0013. Web. 27 Mar. 2013.
Accuracy: Some measurements may be imprecise, as it was difficult to straighten out the radicles against the ruler. Also, there was minor confusion in the recording of data when it came to percentages, such as the petri dishes being labeled incorrectly at first.
Real-Life Application: Knowing the LD50 of a substance can help to determine just how dangerous it is to ingest. In a case of poisoning recently, a man poisoned his girlfriend with Visine eye drops (Wired), the LD50 of which was found to be 345 kg/mg. People assume poisoning via Visine is irritating but harmless because of the movie "Wedding Crashers," but in actuality it's poisonous enough to kill. When people don't grasp the toxicity of substances, they can endanger others.
Works Cited
Blum, Deborah. "Just an (Eye) Drop of Poison." Wired.com. Conde Nast Digital, 23 Mar. 0013. Web. 27 Mar. 2013.