Influence of road salt on new born plants
By Arianne van Rijn and Roos Boersma
Date of submission: 8th April 2011
Summary
A plant tries to reach a balance between the concentration in its cells and in its
environment. We investigated what the influence of salt is on the germination of
seeds. The first experiment demonstrates that NaCl (road salt) influences the
germination of seeds. The second experiment demonstrates that more experiments
are necessary to reach the same result as in the first experiment.
Inquiry question:
What is the influence of salt (road salt) on
the germination of seeds?
During winter a lot of salt is scattered on
the roads. We investigated what the
influence of salt is on roadside plants. Salt
stays in the ground. In spring, osmotic
value in the ground is very high.
Hypothesis
We expect that seeds in a high salt
concentration germinate less, because of
the high osmotic value. The osmotic value
outside the plant is higher than in the cell.
Osmosis theory
‘‘Osmosis is the passage of water from a
dilute solution through a semi-permeable
membrane to a more concentrated
solution (from Nigel D. Purchon)’’ This is
one of the many definitions of the
phenomenon of osmosis.
The semi-permeable membrane can stop
some substance. Cell membranes will
allow small molecules (such as salt NaCl,
Oxygen O2, water H2O, Carbon Dioxide
CO2, Ammonia NH3 (aq), Glucose
C6H12O6) to pass through. Cell
membranes will not allow larger
molecules. A region of high concentration
of water is either a very dilute solution of
something. There is a high concentration
of water.
In the cell there is a higher concentration
of substance. The water concentration in
the environment of the cell is higher. The
semi-permeable membrane will pass
through water by osmosis. The cell will
swell. Cells of plants always have a cell
wall surrounding them. When they absorb
water by osmosis they start swelling, but
the cell wall prevents them from bursting.
The cell is turgid now. Turgid means that
the plant is hard and swollen.
Now there is a balance between the two
concentrations. There is still movement of
water in both directions.
When the concentration of water in the
environment is lower than in the cell, the
water will move through the semipermeable membrane again, but now in
the opposite direction. The cell will lose
water by osmosis and collapse. The cell
becomes flaccid. The cell has
plasmolysed.
Two experiments were done.
The first experiment:
In the first experiment we investigated if
salt always influences the germination of
seeds. This experiment has been done
once. This experiment has kept on for six
days.
There were four Petri dishes. Every dish
contained cotton-wool and fifteen cress
seeds.
The first dish was filled with 23.041 grams
of demi-water.
The second dish was filled with 23.196
grams of demi-water and 0.998 grams of
NaCl
The third dish was filled with 23.001 grams
of tap water
The fourth dish was filled with 23.175
grams of tap water and 1.000 grams of
NaCl.
The second experiment:
On the basis of the result of the first
experiment, a second experiment was
done.
We investigated the influence of a variable
concentration of NaCl in demi-water on the
germination of seeds. This experiment has
been done once. This experiment has kept
on for six days.
There were seven Petri dishes.
The first dish was filled with a
concentration of 0.02000 mol/L NaCl.
The second dish was filled with a
concentration of 0.01000 mol/L NaCl.
The third dish was filled with a
concentration of 0.005000 mol/L NaCl.
The fourth dish was filled with a
concentration of 0.002500 mol/L NaCl.
The fifth dish was filled with a
concentration of 0.001250 mol/L NaCl.
The sixth dish was filled with a
concentration of 0.0006250 mol/L NaCl.
The seventh dish was filled with a
concentration of 0.0003125 mol/L NaCl.
The molar mass of NaCl is 58,44 g/mol.
We started with 1,169 gram of NaCl,
because 0,02 mol/L * 1L * 58,44 g/mol =
1,1688 gram.
The solution was diluted by blending half
of the previous solution with the same
amount of demi-water.
Results
Experiment 1
Demi-water
Demi-water with NaCl
Tap water
Tap water with NaCl
Burst seeds (pieces)
14
0
13
0
Germinated (pieces)
3
0
1
0
Burst seeds (pieces)
Germinated (pieces)
15
7
6
6
5
4
15
12
7
6
6
5
4
7
Experiment 2
Concentration NaCl in
demi-water
0.02000 mol/L
0.01000 mol/L
0.005000 mol/L
0.002500 mol/L
0.001250 mol/L
0.0006250 mol/L
0.0003125 mol/L
The growing plants all had the same
height. There was no difference between
the height or the colour of the plants.
All the seeds in both experiments had the
same rate of daylight and the experiment
was set in the same spot during one week.
Conclusion and discussion
In the first experiment it is demonstrated
that NaCl (road salt) influences the
germination of Cress seeds. None of the
seeds germinated.
In the second experiment it is
demonstrated that almost all the seeds
germinated. This does not correspond with
the hypothesis. The salt has no influence
of the germination of seeds. This does not
correspond with the theory of osmosis.
The seeds should not have broken open in
a high salt concentration, but they did. We
cannot explain this result of the
experiments.
Evaluation
To prove that the theory of osmosis is true
- as well on germination of Cress seeds the experiment has to be done more
times. The experiment has to be done in
the same circumstances with the same
concentrations of NaCl. The results have
to be put in a diagram. The diagram shows
a clear result.
The concentrations of salt are correctly
calculated. All the seeds have had the
same time to develop and to germinate.
They had the same amount of (day)light.
Bibliography
http://www.purchon.com/biology/osmosis.htm
A site by Nigel D. Purchon, a biologist.
http://www.experimenten.nl/tuinkers.html
A Dutch site with a very simple description of the
experiment.