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Studying the Effect of Salt on Cress Germination

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PLANNING Initial Method 1. Prepare 8 sterile Petri dishes with a perfectly fitting circle of cotton wool and filter paper, this will sit on top of the wool 2. A control dish must also be set up using the same steps as above 3. Weigh out 8 different salt measures, at 0.25, 0.5, 0.75, 1, 1.25, 1.5 and 1.75 4. Measure out 8, 50ml beakers of distilled water 5. 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 6. Add one drop of Plant nutrient growth (e.g. baby bio) to each solution 7. 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 8. Add 10 Cress seeds to each of the 8 solutions and place the lid on the dish 9. Place the dishes in are area which is well lit by natural light 10. Check the dishes each day for a week 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) ...read more.


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) SALT (grams, g) SALT CONCENTRATION (%) NUMBER OF SEEDS GERMINATED (%) 0.25 0.5 100 0.5 1 70 0.75 1.5 60 1 2 40 1.25 2.5 0 1.5 3 0 1.75 3.5 0 0 0 100 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) ...read more.


11. Repeat this process again so that you run two sets of 8 salt concentrations OBSERVING AND RECORDING Table of Results SALT (grams, g) SALT CONCENTRATION (%) NUMBER OF SEEDS GERMINATED (%) 0.05 0.1 92.5 0.2 0.4 65 0.35 0.7 40 0.5 1 20 0.65 1.3 12.5 0.8 1.6 0 0.95 1.9 0 0 0 97.5 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 Category Data 1 Rank R1 Data 2 Rank R2 d = (R1 - R2) d2 1 0 1 97.5 8 -7 49 2 0.1 2 92.5 7 -5 25 3 0.4 3 65 6 -3 9 4 0.7 4 40 5 -1 1 5 1 5 20 4 1 1 6 1.3 6 12.5 3 3 9 7 1.6 7 0 1.5 5.5 30.25 8 1.9 8 0 1.5 6.5 42.25 n 8 Sum 0 167 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. ...read more.

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A well conducted investigation with clearly identified variables. Appropriate statistical analyses successfully carried out but their interpretation should refer to levels of significance, chance and probability.

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Marked by teacher Adam Roberts 25/10/2014

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