Air pollution: Does sulphur dioxide affect seed germination?

The aim of this experiment is to find out how sulphur dioxide affects seed germination. This will be done by adding different concentrations of sodium metabisulphite to cress seeds, which will be germinated in a polythene bag for a week. The different solutions will be tested by different users, the concentration you need to use will be assigned. After a week, the results will be notated and plotted on a graph. The graph will indicate the severity of sulphur dioxide during seed germination.

Materials required:

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* filter paper

* Petri dish

* a pencil

* watch glass

* tongs

* cotton wool

* Different concentrations of Sodium metabisulphite

* polythene bag

* a wire

* tap water

* 25 Cress seeds

Method:

1. Get a piece of filter paper and soak it with tap water.

2. Place the soaked filter paper in a Petri dish.

3. Gather a pencil, and mark a 5 x 5 grid on the filter paper.

4. Place 25 cress seeds on the marked grid.

5. Using tongs, dip a piece of cotton wool in 1% concentrated Sodium metabisulphite solution.

6. Place the soaked cotton wool on a watch glass.

7. Place the watch glass containing the sodium metabisulphite and the Petri dish containing the cress seeds beside each other, in a polythene bag.

8. Tie the bag using the wire.

9. Place it on a windowsill, and leave it to germinate for a week.

10. After a week, record the number of seeds germinated.

11. Plot a graph using the results.

Concentration of Sodium metabisulphite (%)

Number of seeds germinated

Percentage germination

(%)

Average stem length

(Cm)

0

21

84

1.5

0.01

18

72

0.6

0.05

17

68

0.9

0.1

13

52

0.42

0.25

2

8

0.25

1

0

0

0

2

0

0

0

Conclusion:

During the experiment each group was assigned a different concentration to test, the one that I recorded was 1%. From my individual experiment I have found that 1% Sodium metabisulphite is enough to stop a plant from germinating. From my results I have found that sodium metabisulphite decreases the number of seeds germinated, as the concentration of the solution increases. When the solution reaches 1% it becomes a limiting factor, because it has will have stopped the growth and increasing the concentration further will not affect it. This experiment has shown, that the release of sulphur dioxide needs to be kept at a minimum.

To keep my result valid with the rest of the results, I have placed the polythene bag, on the same windowsill, so the amount of light the seeds received is the same. Another factor which made the results valid, is the 5 x 5 grid, which made sure the distance between the seeds is the same and each seed has got an equal surface area to absorb light. Also the amount of water available to the seeds was near enough equal.

To make the results reliable, I have compared my results with people who used the same concentrated solution.

The result highlighted on the table, is most likely to be incorrect, incorrectly measured or another factor may have affected its growth.

Evaluation:

The experiment overall went well. I have found that sulphur dioxide does affect seed germination, when in the right concentration it completely stops the germination. The experiment was made valid and reliable. However to improve it for the future, the experiment can be made more reliable by repeating it several times and taking the average number of germination.

To increase the validity I could have ensured that the amount of water was fully equal in each Petri dish.