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.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.

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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


Properties – a white crystalline solid, stable, melting point 804 ºC, boiling point                                                                                   1413 ºC


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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. 4 Stars