Lab report requirement:
1.You need to finish the activity and submit the data table and two graphs (dose vs. # of seeds germinated; dose vs. mean radicle length(mm))
2.Answering questions in ‘Analysis”
LD 50 Lab Name: _____________ Date:_____________ Introduction and Problem: The LD-50 of a compound simply means the individual dose of that compound that is required to kill 50% of a population of something. This is calculated in order to assess the risks of certain chemical compounds. By using a dose-response experiment in which many different populations of test organisms are exposed to various doses of that compound, scientists are able to calculate the LD-50 of the compound. The data can then be used to discuss and manage risks involved when using that compound. According to the background information provided for this lab, it is suspected that salt applied to highways for deicing may affect the growth of nearby vegetation. By conducting this dose-response experiment using radish seeds and different salt concentrations, the amount of salt required to kill 50% of a radish seed population will be calculated, thus evaluating the risk of deicing highways with salt. Many things discussed in this lab include a dose-response curve as well as serial dilution. A dose-response curve is a curve plotting the relationship between the dose of a drug administered and its pharmacological effect. On the contrary, serial dilution is a lab technique in which a substance is decreased in concentration in a series of proportional amounts. Hypothesis: If radish seeds are exposed to 12.5% of the salt solution, then 50% of the radish seed population will die, but, the seeds germinated radicles will be much larger than those of the control group. Parts of an Experiment: · Independent Variable: Concentration of salt added to the radish seeds. · Dependent Variable: Number of germinated seeds and the average length of them. · Controlled Variables: plastic bags, distilled water, napkins, amount of sunlight, amount of time grown. · Control Group: Seeds exposed to distilled water only, and 0% salt. · Experimental Group: Seeds exposed to numerous concentrations of salt Materials: · 6 ziploc bags · 60 seeds ( you can use other seeds) · 12 napkins · Concentrated salt water solution (Pour 4 oz. of water into a pan, and slowly add salt. When excess salt starts to rest at the bottom of the pan. Or you can use Nutri-SeaWater for aquarium) · Distilled water (bottle water) · Graduated cylinder (any cylinder) · Metric ruler Methods and Procedure: 1. Use the graduated cylinders and test tubes to prepare the various concentrations as shown below. (see photos in the end) 2. Label all six bags with your group number, the dish #, and a percent concentration of chemical: Dish #1: 0% (control group) (20 ml water and 0 ml salt water) Dish #2: 6.25% (18.75 ml water and 1.25 ml of salt water) Dish #3: 12.5% (17.5 ml water and 2.5 ml salt water) Dish #4: 25% (15 ml water and 5 ml salt water) Dish #5: 50% (10 ml water and 10 ml salt water) Dish #6: 100% (20 ml salt water) 3. Put two napkins together and cut them so that they fit into the bag. 4. Put on the safety goggles and latex gloves. Carefully pour the salt solution onto the napkins, making sure to match the numbers and concentration percentages of the dish. 5. Count out 10 seeds. Carefully place the seeds on the moist napkins in the bag. 6. Repeat steps 3-5 for the other dishes. 7. Place the seed dishes in a stack, lying flat with the seeds up. 8. Let the seed germinated for three days. Collecting Data: 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. 1. 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. 2. 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).” Data table: Replicates-radicel length (mm) Concentration of salt solution (ml) % of seeds germinated 1 2 3 4 5 6 7 8 9 10 Mean radicle length (mm) 0% 0.00ml 6.25% 1.25 ml 12.5% 5.0ml 25% 5.0ml 50% 10.0ml 100% 20.0ml Plotting Results: 1. 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. 2. 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. 3. Make a line graph to show the percentage of seeds that germinated for each salt solution. Analysis: 1. What did you observe in this experiment? 2. Based on the dose-response curves, what was the LC-50 of salt on radish seeds predicted? 3. Any conclusions you can draw from this activity? Lab report requirement: 1. You need to finish the activity and submit the data table and two graphs (dose vs. # of seeds germinated; dose vs. mean radicle length(mm)) 2. Answering questions in ‘Analysis” Photo 1 Photo 2 Photo 3