Procedures:
- I took five Petri dishes with lids and then labeled them pH 3, pH 4, pH 5, pH 6 and pH 7.
- I placed a disc of filter paper in the base of each dish (they had to be slightly cut as they were too big for the Petri dish)
- Then, 5cm³ of sulphuric acid pH 3 was poured into the dish labeled pH 3. it was poured in a way for it to be evenly distributed.
- I repeated the procedure in 3. for the other solutions and respective dishes
- 50 similar sized seeds were selected; the size was estimated by putting them on a sheet of graph paper.
- I placed 10 mustard seeds evenly on the filter paper in each dish. To ensure they were evenly placed, I used a ruler to measure the distances between each seed.
- Each day the seeds were observed for signs of germination and growth and for the measurements to be made.
- All the dishes were exposed to the same temperature (room temperature) as well as to the same oxygen availability: fresh air was only introduced to the dishes whenever they were observed, so they were exposed to air for and at the same time.
Data collection:
The data collected is presented below in 4 different tables, each of them corresponding to each pH value.
Table 1- pH 3
Table 2 - pH 4
Table 3 - pH 5
Table 4 - pH 6
Table 5 - pH 7
Tables 1, 2, 3, 4 and 5 (pages 3 and 4) were made with the data collected from the 4 readings made throughout the week. Below, Table 6 shows a synopsis of the other tables presented above by showing the average values – with the respective standard deviations – for the length of root, length of leaves and length of stem.
Table 6
Table 6 (above) contains all the data collected during this investigation. The graphs presented in Data Processing and Presentation will be based in the values shown on this table.
Data Processing and Presentation:
Graph 1 (left) – Average
length of
stem for each
level of pH
Graph 2 (left)
– Average
length of
root for each
level of pH
Graph 3 (left)
– Average
length of
leaf for each
level of pH
Conclusion and evaluation:
With this investigation on the effect of acid rain in germination and growth of mustard seeds we can confirm our hypothesis to a certain extent, as mustard seeds grew more when in a neutral pH (i.e. pH7). This is due to the fact that the optimum pH for germination and growth of mustard seeds is a neutral pH, therefore the existence of better results for pH 7 than for any other value of pH. However, contrary to what was expected, pH 3 also showed very positive results if we have in account that it is a very low and therefore very acidic level of pH. For example, when we compare the average length of root of pH 4 by the time of reading no. 4 with that of pH 3, there is a big difference: while pH4 has an average root length of 1,33±0,38cm, pH3 has 4,66±1,60cm. As expected, pH7 showed the highest root development with an average root length of 5,01±1,78cm in reading 4. Surprisingly, pH6 proved to be the worst level of pH for mustard seeds’ development: by the last reading (on the 13th May) all the roots of the germinated seeds were rotten. On the other hand, the leaves have developed more in pH 6 than in any other level of pH – see graph 3 – as by reading no. 4 pH6 had an average leaf length of 3,9±0,30mm whereas the second best level of pH – pH7 – had an average of 3,17±0,38mm. The pH level showing the lowest leaf development was pH3, with an average of 2,57±0,50mm, which does not differ much from those of pH4 and pH5 but has a difference of more than 1mm when compared to the average of pH6. Up to now, pH7 is the level of pH that has been showing the most proportional development if compared for example to pH6 – where all the roots were rotten but where there was a significant leaf development – or even pH3, whose statistics show it had the lowest leaf length despite having had the second best root length. After analyzing more carefully the column concerning the length of leaves in Table 6 (Page 5) we can conclude that it was only in this column that our hypothesis proved to be correct: the higher the pH level, the higher the average of leaf length. Although pH6 had actually a higher leaf length than pH7, we can consider it as being already a neutral pH: acid rain, for example, usually has a pH of 5. The number of leaves in each pH level showed a tendency to increase in pH’s 4, 5 and 6. In pH6 there was a high increase in the number of leaves between readings 2 and 3, where by reading three it had more 12 leaves than before. By the time of reading 4, despite the fact all the roots were rotten there was a total of 40 leaves which is interesting if we have in account the state of the roots. pH3 shows the lowest number of leaves – 28 – and this number remains constant throughout the week. This is associated to the fact that only 7 seeds germinated from a total of 10, where each germinated seed had a number of 4 leaves. pH7’s number of leaves also remained constant throughout the week: 9 mustard seeds germinated, which gives a total of 36 leaves where, as well as in pH3, each seed that germinated had 4 leaves. In pH4 and pH5, the number of seeds that germinated was 8, however the total number of leaves in each of them was 36. This has to do with the fact that in each value of pH one of the seeds that had not germinated yet started to develop small leaves, however it had neither root nor stem – at least those were not visible – the leaves seemed to grow directly from the seed. Finally, pH3 showed the highest average in stem length: 2,79±0,30cm. pH7 was the second best, with an average difference of 0,09cm. pH6 showed the lowest average for stem length, not even reaching an average of 2cm. This shows, once more, hat the seeds in pH6 developed more the growth of leaves rather than the growth of the root or stem, and there might be an explanation for the roots being rotten: they possibly were not able to support such development in the leaves in contrast with the poor development observed in the stem and the roots themselves.
After this analysis, we can conclude that the level of pH that showed better results in the germination and growth of mustard seeds was pH7, where 9 seeds out of 10 germinated and showed a good and proportional growth and development. Despite having also had very good results having in account it was a very acidic level of pH, only 7 seeds germinated in pH3 from a total of 10, which shows a lower rate of success in germination and growth when compared to that of pH7.
The results obtained from this investigation are accurate as many procedures were taken in order to achieve that. Firstly, the size of the seeds was measured in graph paper in order to ensure their size would be the same therefore that would not have an effect in the results: all the seeds were 2mm diameter. In addition, the spacing between the seeds when they were put in the Petri dishes was also the same – 2cm – to make sure they would all have the same space for growing and they were all under the same conditions. Furthermore, when the readings were made all the seeds were exposed to the same oxygen availability as well as to the same light intensity and temperature, so by taking these procedures all of them had the same conditions to germinate and develop their features – root, stem and leaves. Secondly, a pH meter was used to check the different pH’s to make sure they were not higher or lower than the expected. Thirdly, a ruler measuring in mm was used to make de measurements concerning the lengths.
Although a ruler measuring in mm was used, sometimes there were difficulties in making the measurements due to the lack of space to place the ruler in the Petri dishes – they were perhaps too small – so a bigger container should have been used to place the seeds: that would allow a higher spacing between each seed and would have made the measurements easier to make.