Equipment List
- Cress seedlings (bag)
- Petri Dishes
- Filter paper and Cotton wool for each dish
- Distilled Water
- Beakers and measuring cylinders
- Scales
- Spatula
- NaCl (rock salt)
- Plant growth solution – baby bio
Risk Assessment
NaCl
Properties – a white crystalline solid, stable, melting point 804 ºC, boiling point 1413 ºC
Figure 1 – risk table
Table of Variables
Figure 6 – variables table
Control Variables, firstly all the repeats and solutions were placed in front of a window where every dish would receive equal amounts of light with no sun blockage and even coverage, the temperature would have also been even for all of the dishes as they were placed away from any heat sources and would all receive the same room temperature. I controlled the samples of cress water and salt by ensuring they were all measured correctly and from the source. I used the same type of cress and salt which were taken from one batch. The water was also all used from the same bottle.
Table of results (preliminary)
Figure 2 – preliminary results
The results I have recorded are sufficient to use in a spearman rank coefficient data test as I am looking for a correlation and trend and have taken a suitable amount of repeats and tests to gain a result from the stats test. I also have no anomalies in my original results as they all appear to follow a trend
Statistical Data Test – Spearman Rank Coefficient
For my main experiment, I have chosen to analyse the results using a Spearman’s Rank Correlation Coefficient test. This should allow me to assess whether there is significant correlation between the concentration of salt (NCaL) and the germination of seeds. This test is appropriate as I am taking readings for 8 different concentrations, and both of the variables recorded (germination % and concentration) are continuous.
Figure 4 – preliminary data test
The spearman rank correlation coefficient equalled – 0.96 and the critical value were 0.64 giving a significant correlation (which was negative) therefore disproving my null hypothesis “salt has no effect on the germination of cress seeds.” The results show that the larger the salt concentration gets the lesser the cress seed germination is.
figure 5 – preliminary results graph
The preliminary test was successful, and I judged that 0.95 g of Salt per 50ml would be the highest concentration I would use. Results from the test (fig 5) show that germination in the presence of 1.25 g to 2g (2.5 – 4%) salt concentration is severely inhibited. No concentration of salt appeared to increase the rate of respiration (in comparison to the control).
The preliminary test showed that my method appeared to work, however I could change it to create a more reliable test using closer measurements of salt, this will be shown in my revised method for my main experiment. I will take readings from 0g-0.95 per 50ml of copper sulphate at 0.15g intervals. However, I was concerned that the electronic balance was not sensitive enough so measure differences in 0.01g of mass. So for my main experiment, all other factors involved will remain the same as they have seemed to be correct, the preliminary test can be considered great success.
Revised Method
- Prepare 8 sterile Petri dishes with a perfectly fitting circle of cotton wool and filter paper, this will sit on top of the wool
- A control dish must also be set up using the same steps as above
- Weigh out 7 different salt measures, at 0.05, 0.2, 0.35, 0.5, 0.65, 0.8, and 0.95 grams
- Measure out 8, 50ml beakers of distilled water
- Add the one measure of salt into a beaker (1 beaker for each weight) and stir until the salt is dissolved and cannot be seen
- Add one drop of Plant nutrient growth (e.g. baby bio) to each solution
- Add each solution into individual Petri dishes which were made up earlier on, make sure the cotton wool and filter paper are allowed a small amount of time to absorb as much water as possible before the next step
- Add 20 Cress seeds to each of the 8 petri dishes and leave the lid off of the dish
- Place the dishes in are area which is well lit by natural light
- Check the dishes each day and top up each dish with the same solution if it is becoming dry, add the same amount to each dish (record what you add)
- Repeat this process again so that you run two sets of 8 salt concentrations
OBSERVING AND RECORDING
Table of Results
Figure 7 – Main investigation results
The above results show a general correlation indicating that increased salt concentrations reduce the germination of cress seeds, however I will analyse this later
Statistical Data Test – Spearman Rank Coefficient
Figure 8 – Main investigation statistical test
The spearman rank correlation coefficient equalled – 0.98 and the critical value were 0.64 giving a significant correlation (which was negative) therefore disproving my null hypothesis “salt has no effect on the germination of cress seeds.” The results show that the larger the salt concentration gets the lesser the cress seed germination is.
INTERPRETATION AND EVALUATION
Figure 9 – Main Investigation results graph.
