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Studying the Effect of Salt on Cress Germination

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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.
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    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)
  11. Count and record the percentage

I chose to carry out my method in this fashion as it gave me the best way to see which salt concentration had the biggest effect.

I chose 8 solutions as it gives me a good range to monitor the salinity effects. The solutions are based on findings in earlier research and I chose to go up to 1.75 grams to see whether this would affect cress regardless of it being a particularly high concentration. The amounts of salt correspond with the 50 ml measurements (which is as much as a Petri dish can hold without risk of spillage) to make the correct percentages I needed to study the effects closely. The test will run for a week as cress is expected to grow in 3-6 days, the extra day allows for poor weather affecting the light and other extraneous variables which I shall go on to explain further.

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 �C, boiling point 1413 �C

HAZARD

RISK

HOW TO REDUCE RISK

EMERGENCY ACTION

Soluble in substantial colourless amounts

Vomiting, stomach related illnesses

Do not place near drinking water and clearly label the salt solutions

Ensure the consumer is feeling well and hydrate with clear drinkable water

Salt entering the eye

Irritation and surface scratches

Wear Safety Goggles, keep away from the face

Flush the eye with clean water, seek medical advice if severe

Glass beakers

Cuts and grazes

Keep away from edges and act in a careful manner when carrying

Clean up all broken glass and dispose of it safely. If cut sterilise and bandage, if severe seek medical attention

Scissors

Cuts

Use safety blunt ended scissors and use them with caution

If cut sterilise and bandage, if severe seek medical attention

Figure 1 – risk table

Table of Variables

Independent

Dependent

Control

Extraneous

Salt concentrations (%)

The % of cress which has germinated

The distilled water, all from the same source and bottle

The weathers effect on how much light the cress received per day

All repeats received the same amount of light

Consistency of the room temperature

All repeats were done at the same temperature

Diseased or damaged cress

All cress was taken from the same plot and bag

All petri dishes were sterile

All salt was weighed and measured using the same scales

All water was measured in the same measuring cylinder

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)

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) are continuous.

Category

Data 1

Rank R1

Data 2

Rank R2

d =

(R1 – R2)

d2

1

0

1

100

7.5

-6.5

42.25

2

0.5

2

100

7.5

-5.5

30.25

3

1

3

70

6

-3

9

4

1.5

4

60

5

-1

1

5

2

5

40

4

1

1

6

2.5

6

10

3

3

9

7

3

7

0

1.5

5.5

30.25

8

3.5

8

0

1.5

6.5

42.25

n

8

Sum

0

165

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

  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 7 different salt measures, at 0.05, 0.2, 0.35, 0.5, 0.65, 0.8, and 0.95 grams
  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 20 Cress seeds to each of the 8 petri dishes and leave the lid off of the dish
  9. Place the dishes in are area which is well lit by natural light
  10. 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)
  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.

Cite this Studying the Effect of Salt on Cress Germination

Studying the Effect of Salt on Cress Germination. (2017, Jul 22). Retrieved from https://graduateway.com/studying-effect-salt-cress-germination-178/

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