In this investigation, we are researching and investigating whether the concentration/percentage of NaCl (salt) in water affects the germination rate of seeds and if so, which concentration germinates the most seeds. We will formulate our research by conducting an experiment in which we will observe the germination of seeds in various concentrations of salt water and evaluate the results gathered. In particular, we will measure the percentage of seeds germinated in one week and formulate our conclusions from there.
I hypothesise that the highest percentage of seeds will germinate in the petri dish that contains the lowest percentage of NaCl in water- 0.5% salt salinity and the percentage will decrease as the percentage of salt in the solution increases. I predict this because I know from prior knowledge that seeds need to be able to absorb H2O to germinate and salt prevents this. So if we increase the amount of salt and therefore, decrease the amount of H2O in the solution, germination of seeds will occur less than those in lower percentages of salt, thus allowing for the 0.5% solution to germinate the most seeds as it contains the least amount of salt out of our five different samples.
The independent variable (the variable being changed): The independent variable is going to be the concentration/percentage of salt in water (%). This variable will be changed and a different percentage of NaCl will be used in every petri dish. We will measure and change the concentration of NaCl with water for each petri dish by measuring and pouring 5mL of solution from a particular solution bottle and into a petri dish, using a different solution bottle-which contain different concentration of salt-for each dish.
The dependent variable (the variable being measured): The dependent variable is going to be the percentage of seeds that germinate over one week in each petri dish/NaCl solution. We will count the total number of seeds in each petri dish and after one week; count the number of seeds that germinated so that we can calculate a percentage.
The control variables (the variables kept the same): The other variables, which we need to keep constant, are:
* The same number of seeds used for each petri dish (10 seeds). To keep the amount of seeds the same for each sample, we will count out five groups of 10 seeds and then spread them evenly in each petri dish.
* The same fertilizer used to place around the seeds in each sample and the same quantity of the fertilizer. We will control this variable by ensuring that we use six cotton wool balls in each petri dish and we will make sure that no soil is placed in any of the dishes.
* The same seed species used (cress seeds) the same depth of planting. To make sure that all the cress seeds are planted the same distance into a cotton wool ball, we will carefully place them on the surface of the cotton wool ball, ensuring that we do not apply any pressure.
* The same type of container/petri dish used for each sample and the same type of lid used. To ensure that the same type of petri dish is being used, we will measure the diameter of each of them and ensure that they are all made of plastic. So that the results are accurate and the same conditions are kept for each trial, we will place a lid tightly onto each petri dish, restricting airflow to the seeds.
* The same length of time each seed spends in a petri dish before being observed. To keep this variable constant, we will leave each seed in the petri dish for one week before we observe them. This is the amount of time they have to be germinated in and will be length of our experiment.
* The same volume/amount of H2O (including salt) used in each petri dish. To control the amount of water poured in each petri dish and ensure that it is the same temperature for each sample, we will carefully measure out 5mL of a NaCl solution in a measuring tube and pour drops evenly around the 10 seeds. To keep the temperature the same, we will ensure that each solution bottle is at room temperature.
* The same spacing of seeds in the petri dish and the same gap between them (1cm). To ensure that the experiment is fair, we will equally space the seeds around the edge of each petri dish and ensure that there is 1cm gap between them.
* The same conditions present around the experiment (room temperature, sunlight, disturbance, humidity, etc.). To keep the room temperature and sunlight consistent for each petri dish, we will place each petri dish next to each other at the same location. This way, the room temperature will be the same for all of them and the amount of sunlight will barely change. The level of disturbance around each trial will be kept to a minimum, allowing for none of the seeds to be knocked of a cotton wool ball.
* 5 mL NaCl 0.5% solution
* 5 mL NaCl 1% solution
* 5 mL NaCl 1.5% solution
* 5 mL NaCl 2% solution
* 5 mL NaCl 2.5% solution
* 1x Measuring Tube
* 5x Petri-Dishes with lids
* 50x Cress seeds
* 1x Desk
* 3x Lab coats
* 1x Laptop
* 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.
NaCl (%-0%=No Salt)
No. Of Cotton wool Balls
Amount of NaCl and Water (mL)
1. Collect all necessary equipment, cress seeds and all other substances listed above and put on the lab coats.
2. Place the five petri dishes next to each other with their lids and make sure that they are the same size and make.
3. 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.
4. Divide the 30 cotton wool balls into groups of six so that there are five groups.
5. 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. Macintosh HD:Users:160161:Desktop:Screen Shot 2013-08-26 at 7.53.24 PM.png
6. 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.
7. 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.
8. 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%.
9. 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. Macintosh HD:Users:160161:Desktop:Screen Shot 2013-08-26 at 7.56.08 PM.png
10. 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.
11. 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.
12. 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.
13. Once finished, return equipment and throw out seeds and cotton wool balls.
14. 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.
Graph: I think the best kind of graph to use to display these results would be to create a line graph:
Macintosh HD:Users:160161:Desktop:Screen Shot 2013-08-24 at 5.03.21 PM.png
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.
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.
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.