EXPERIMENTAL PLAN
Materials/Equipment:
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5 mL NaCl 0.5% solution
- 5 mL NaCl 1% solution
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5 mL NaCl 1.5% solution
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5 mL NaCl 2% solution
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5 mL NaCl 2.5% solution
- 1x Measuring Tube
- 5x Petri-Dishes with lids
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50x Cress seeds
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1x Desk
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3x Lab coats
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1x Laptop
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1x Marker
- 30x Cotton wool balls
Setup & Plan:
Here are the details of how we will conduct our experiment and the measurements we will make:
Our group will calculate the percentage of seeds germinated in each trial by using a basic formula. We will count the total number of seeds for each concentration, count the number of seeds that germinate and use these numbers to figure out the percentage using a calculator. After our data has been collected using the above method and formed into a table, we will process and convert it into a line graph with a “line of best fit”. Our experiment will be set up (like in the above image) with the petri dishes placed next to each other for a week and the seeds germinating on the surface of the cotton wool so that we can observe the seeds without disturbing them.
Some techniques we could use to achieve prime accuracy and precision are:
- Dropping the solution of salt and water directly on the seeds so that none of it is wasted and some seeds get less than others.
- Using the same scale of germination for each seed- allowing for two exact same seeds that are on the border line between germinated and not germinated to both be called germinated/not germinated rather than different decisions.
- Comparing our results with another group to see if there are any anomalies in our data.
Method:
- Collect all necessary equipment, cress seeds and all other substances listed above and put on the lab coats.
- Place the five petri dishes next to each other with their lids and make sure that they are the same size and make.
- Label with the marker a different NaCl percentage on each lid (0.5%, 1%, 1.5%, 2%, 2.5%). Ensure that lids do not get mixed up with each other.
- Divide the 30 cotton wool balls into groups of six so that there are five groups.
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Place each group of cotton wool balls inside a different petri dish and space them out evenly in the dish, ensuring that there is very little gap between them.
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Divide the 50 cress seeds into groups of ten and place each group into a different petri dish. Place them gently on the surface of the cotton wool balls, spreading them evenly around the edge with a 1cm gap between them.
- Measure out 5mL of the 0.5% NaCl solution in a measuring tube and carefully drop the solution on the seeds in the respective petri dish with the label: 0.5%. Ensure that all of the solution is dropped on the seeds and not on the side.
- Repeat the step 7 with the 1% solution; ensuring the measuring tube is washed before. Remember to pour the solution on the seeds in the petri dish with the label 1%.
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Repeat step 7 again with the 1.5%, 2% and 2.5% NaCl solutions, remembering to wash the measuring tube each time and pouring the solutions to their respective labeled petri dishes.
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Place on the lids on each petri dish-tightly and with the same amount of force each time so that airflow to the seeds is the same for each petri dish.
- Move the petri dishes to a suitable location where they will get enough sunlight as well as not be disturbed by activity around them. Leave them there for a week.
- After the week has passed, open their lids and count how many seeds germinated in each petri dish. Record your results in a table and use a calculator to work out the percentage that germinated.
- Once finished, return equipment and throw out seeds and cotton wool balls.
- Write up report, ensuring to include a graph and results table.
*NOTE: Capture pictures throughout experiment with the laptop and remember to write down all observations.
RESULTS
Results Table:
Graph: I think the best kind of graph to use to display these results would be to create a line graph:
DISCUSSION
Our results show a wide range of relationships between the data. For instance, the shape of our graph shows that as the concentration/percentage of NaCl increased, the percentage of seeds that germinated decreased. This trend is proven as the concentration that germinated the most seeds was the lowest (0.5%) and the highest concentration germinated the least seeds (zero seeds). Looking at the logarithmic line, it seems as if the trend will continue. There was also no real pattern in the decreasing rate with the line (the blue line) on the graph having different gradients between points. Another pattern was that, usually less of the seeds in the middle germinated than those on the edges. This may have been caused due to the solution gathering around the edges, leaving those seeds with more H2O. The data looks fairly reliable, as there are no anomalies, although the variation of the gradient may have been caused due to a few errors in the setup of some of the petri dishes.
CONCLUSION
In conclusion, the results gathered are sufficient and clearly show that the germination of seeds is affected by the concentration/percentage of NaCl, convincingly answering our research question. Due to this, I proved my hypothesis correct/valid as the 0.5% concentration of NaCl proved to germinate the highest percentage of seeds- germinating 90% of the seeds in its petri dish. The percentage of germinated seeds also decreased as the concentration of salt increased, further proving my hypothesis valid. This is supported by the sufficient data plotted on the graph, which clearly shows evidence of this with the lowest concentration (0.5%) germinating 90% of seeds and the highest concentration (2.5%) germinating 0% of the seeds. The scientific reasoning behind this theory is that, seeds need to be able to absorb H2O to grow and germinate. However, salt-NaCl- prevents this from happening as it drags out the water from the seeds, drying them out and preventing their germination. Thus, as the salt percentage increases, more H2O is absorbed and drawn out, leaving less and less water for the seeds.
EVALUATION
I think our experiment went quite well and we were able to collect all the necessary readings required, encountering very few problems during the experiment and the week. The only major problem that we encountered was placing the seeds with equal gaps and spacing between each other. Although we mentioned in our control variables that we would place each seed around the edges of the petri dishes with equal gap between them (1cm)- we struggled to keep this consistent, as the seeds where hard to place accurately because we tried not to apply any force when dropping them on the cotton wool balls or disturb the other seeds. This was a result of human error, as the seeds had various spacing with some seeds falling of the cotton wool balls, thus impacting their germination. We solved this problem with some other petri dishes by not worrying too much about the spacing but instead placed each seed in the middle of a cotton wool ball so that it didn’t fall off. A minor problem that we experienced was the small sample of seeds initially supposed to be used- only 10 seeds per petri dish-this wouldn’t have been sufficient data. We solved this problem by adding an additional ten seeds to each petri dish so that we could have a larger sample and more reliable data.
Our group collected a range of data that was sufficient for this experiment although a wider range could have been collected with more concentrations/percentages of NaCl used to obtain a more accurate trend line and conclusion as well as a second trial to make it a fairer experiment. As mentioned above, one of the main errors in our data and measurements was the issue of seeds falling of the cotton balls and into empty space away from the water and salt solution. As a result of this, the data collected could be less reliable in a few tests with some seeds not being in as much solution as they were supposed to, thus affecting our final conclusion based on their germination trend. If we were to conduct this experiment again, a larger sample should be used so that the trend is more reliable and greater accuracy should go into the preparation of the setup.
Using our results, we were able to answer our research question in the affirmative that the concentration/percentage of NaCl does affect the germination process of seeds and the most number of seeds germinate when the lowest concentration of salt (0.5%) is used.
Our method was fairly clear, concise and allowed us collect our data in a fairly orderly way, doing so for most tests. It allowed us to complete the experiment with accuracy excluding the human errors present. Although our method is quite accurate, there are many improvements that could be made to it. These include:
- Reducing the chance of human interference affecting the results (different amounts of solution poured on each seed.) Using a fixed amount for each seed (e.g. 1mL)-instead of just trying to divide 5mL across ten seeds- could solve this problem.
- Using a wider range of concentrations so that the trend can become more evident and more precise conclusions can be drawn on the increase/decrease of seed germination rate.
- We could test each concentration of NaCl three or four times and develop an average, excluding results that stand out so that our data becomes more reliable.
- We could leave the seeds for a longer period of time (e.g. one month) in natural conditions such as a pot or flower bed and water them daily with the various concentrations of NaCl and see which seed has grown the most after the one-month.
- We could extend this experiment by investigating whether using a different type of seed effects the germination rate and if so, which species of seeds germinates the quickest and most consistently.
- We could also investigate how long it takes for every seed to germinate for each concentration and whether using soil instead of cotton wool affects the results.