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ib biology sl notes

A Study On The Effect Of Smoke Water On The Germination And Growth Of Eucalyptus Pilularis

UPDATED ON - 15 APR 2020
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A study on the effect of smoke water on the germination and growth of Eucalyptus pilularis

Summary(Nail IB): 


[Comment]: Overall the report is clear, concise and logically structured.

[Comment]: Subject-specific terminology and notation are used throughout.

[Comment]: Student shows a high degree of engagement with the investigation.


Australia is a country where bushfires are commonplace during the summer season, and these fires affect much of Australia's flora. As a by-product of this, numerous native Australian plants that inhabit fire-dependent ecosystems have evolved reproductive strategies to adapt to factors associated with fire. These adaptations that affect their germination can be classified as either physical (derived from the immense heat of the bushfire stimulating a seed to germinate) or chemical (derived from a combination of various chemical elements produced by the smoke that stimulates germination).                              


[Comment]: Investigation set in context and justified.
[Comment]: Smoke water defined
[Comment]: Research question focussed
[Comment]: Methodology approx


This biology laboratory experiment aims to explore the effects of smoke water, a mixture of water, burnt plants and hay, and its effect on the  germination and post-germination growth Eucalyptus pilularis seeds are also known as gum nut or blackbutt, an Australian

the native plant which predominates in forests that are frequently burned.


Research question

Does smoke water stimulate germination and post-germination growth of Eucalyptus pilularis seeds compared to de-ionized water?


Smoke water will successfully germinate more Eucalyptus pilularis than de-ionized water, and thus, as a result of this, the post-germination growth of the Eucalyptus pituitaries seeds by the smoke water will be more effective. Effectiveness, for this experiment, is defined as the height of the seedling that emerges from the germinated gumnut seed. If the various chemicals, such as phosphorous and nitrogenous compounds found in the smoky remnants of organic matter function as chemical triggers, then Eucalyptus pilularis will begin its germination out of its dormant state. These phosphorous and nitrogenous compounds, such as NaN03, KN03, NH4Cl, and NH4N03, that are naturally occurring in organic matter, are not found in de-ionized water (Dixon et al. 1995), and hence, smoke water is predicted to germinate a larger number of seeds and grow more after germination than de-ionized water.



[Comment]: Defines the method to collect relevant data

[Comment]: Method can be easily followed and repeated by others.

Preliminary experiment

[Comment]: Anticipates that method may need modifying. Sufficient data is planned for

[Comment]: Suitable control 

The gumnut seeds were obtained from trees growing in local forestry plantations. It was felt necessary to find out if the gumnut seeds would germinate or not.   1. 50 seeds were planted in 5 Petri dishes of the potting mixture (10 seeds per dish).

    2. Each dish was watered with 10 ml of de-ionized water and left for two weeks at room temperature.

    3. At the end of the two weeks, the numbers of seeds germinating were counted.    


Number of seeds germinating = 22/50

[Comment]: Data displayed from the trial run

Percentage germination = 44%

[Comment]: Appropriate processing

The supply of seeds was considered viable enough to proceed with the experiment. 

[Comment]: Conclusion made from the trial run.



• 10 Petri dishes

• 100g of "Yates premium quality" potting mix

• 5.00g of hay

• 5.00g of Eucalyptus leaves

• 5.00g of grass

• Electronic weighing scale (±0.01g)

• 100 seeds of E. pilularis that are 2.00 mm in diameter (±0.5mm)

• 10.0cm ruler (±0.5mm)

• 100ml of de-ionized water to create the smoke water

• 100ml of de-ionized water to create the control

• Tea strainer

• 3 x 250ml graduated beaker (±0.4mL)

• Matches

• 2 Sand baths

• 2 thermometers (±0.05°c)

To create the smoke water

    1. Place 5g each of the hay, grass and Eucalyptus leaves into one of the 250ml beakers.

    2. Ignite the organic matter with a match so that they catch on fire. Let them burn until they are all charred.

    3. Measure 100ml of de-ionized water with the second 250ml beakers. Pour this water into the first beaker with the leaves, hay, and twigs and leave to infuse for 5 hours.

   4. Strain the smoke water mixture into the third measuring beaker using the tea strainer, ensuring that you are only left with the liquid remnants.



Care should be taken when burning the organic matter, this should be carried out in a ventilated area and the beakers should be made of heat resistant glass.

[Comment]: Safety risks assessed


Germination and growth

    1. Set the sand baths to 30 degrees Celsius and place a thermometer in each one to verify the temperature setting.

    2. Place 5 Petri dishes into one sand bath and the remaining 5 Petri dishes into another. One will be our control and one will be our test.

[Comment]: Plans for sufficient data

    3. Measure out 10 x 10.0g of the potting mix using the electronic weighing scale and place 10.0g into each one of 10 Petri dishes. 5 dishes for smoke water treatment and 5 dishes for de-ionized water treatment.

    4. Sow 10 gumnuts into each Petri dish and submerge them into the potting mix at a consistent depth of 0.5cm. Place the seeds towards the edges of the Petri dish so they can be observed through the glass without having to disturb the seeds to observe them.

[Comment]: Plans for sufficient data

    5. Water the control sand bath at 8:15 am with 10ml of de-ionized or smoke water each day for fourteen days.

    6. After 14 days, count the number of seeds germinated (distinguished by the emergence of the seedling) and measure the height of the emergent seedling in the test and the control groups with the 10.0cm ruler. The seedling height is measured from the soil surface to the highest part of the stem.

[Comment]: Correct definition of germination

    7. Repeat the set up once to ensure sufficient data.

[Comment]: Plans for sufficient data

Controlled Variables

[Comment]: Thorough consideration of the other factors that may influence the investigation

    • The same volume (10ml) of liquid is added to each dish at the same time (8:15 am) each day throughout the 14 days.
    • All 100 E. pilularis seeds that were used in this experiment were kept within a size range of 2.00mm in diameter

    • The water used to create the smoke water was de-ionized water like the control, which allowed consistency between the control

       and the test groups.

    • The temperature of the seeds was kept constant at 30.0°C by the sand baths.

    • The potting mix for the seeds was from the same brand, "Yates premium potting mix" and the mass of potting mix used for the seeds Was kept constant at                10.0g.

    • The same amount of light was assumed to be received for each plant as the experiment was conducted in the same location on the same days.

    • The seeds were placed at a depth of 0.5cm into the soil in the Petri dish.

The experiment continued for fourteen days to allow for sufficient time to gauge the effect of the different water types, the manipulated variable. Both sand baths set at the same temperature are placed next to each other, as specified by the method, and they are assumed to be receiving equal amounts of light. The potting mix was taken from the same batch, so all samples could be assumed to contain the same ratio of ingredients. Furthermore, the E. pilularis was submerged into the potting mix at a consistent depth of 0.5cm and towards the edges of the Petri dish to allow for observations to be made through the glass without having to disrupt the seeds to observe them.


Our method of data collection for this experiment is to count the seeds that successfully germinated from the different Petri dishes in the control and test groups respectively, the measured variable. This is done by observing through the side of the Petri dish whether the seed coat has broken and the seedling has emerged. The other way to collect data in this experiment is to measure the height of the seedlings (from the soil surface to the seedling tip) of the experiment. The difference of the germinated seeds after the 14 days between smoke water and de-ionized water was determined using the χ2 test for the germination and the t-test for the growth of the seedlings.

[Comment]: Appropriate method of analysis chosen


    • The light is of the same intensity because the seeds will be set up side by side.

    • The de-ionized water contains the same impurities

    • The potting mix contains the same amount of its constituent components.

    • The impurities and chemical elements in the air will be the same for both sets of seeds.

    • The gumnut seeds are all composed of the same percentage of elements.



[Comment]: Adequate qualitative observations made

        • The E. pilularis seeds were no bigger than 2mm and were brownish-black in color. There were no obvious signs of previous

            germination or cracking of the outer seed coat.

        • The smoke water was distinctive from the de-ionized water. The de-ionized water was clear, as one would expect if it had been filtered. The smoke water, however, had a blackish, straw-colored hue, due to its absorption of the remnants of the burnt organic matter.

        • Definite germination was seen on a lot more seeds with the smoke water than with the de-ionized water.

        • The E. pilularis subjected to smoke water germinated earlier on average than the seeds subjected to de-ionized water. Seeds with smoke first signs of water  Started showing germination as early as 7 days when their seed coats started to split to allow the seedlings to merge. In comparison, the de-ionized watered
          seeds took up to 10 days to start showing germination.

        • The E. pilularis that were germinated by the smoke water tended to have larger seedlings emerging from the split seed coat.

        • The E. pilularis that were watered with the smoke water had significantly larger cracking of the seed coat, allowing for more space for the seedlings to grow  And extend outwards from the shell.

       • The color of the seedlings in both experiments was a distinct dark purple color and leaves appeared only on the smoke water experiment,
        with a maximum of 2 small, juvenile leaves found, measuring no more than approximately 50.0mm.

Number of seeds successfully germinated

To determine the number of seeds that were germinated successfully, the number of seeds that showed distinct cracking of the seed coat and the emergence of the seedling for both the smoke water and the de-ionized water test groups was counted and placed into the table below. The raw data is presented in appendix A.


Water Type

[Comment]: Data table set in context. Clear, unambiguous presentation


Numbers germinated (/50)


[Comment]: Data analysis can be followed (no need for a worked
example here)


[Comment]: Uncertainties missing but not
considered relevant here for a count. However, uncertainties ±2% could have featured for the percentage of germination data




















From the processed data that inform us about the number of seeds successfully germinated, we can see that smoke water germinates, on average.















[Comment]: Appropriate graphical presentation of processed data




















[Comment]: Clear presentation of the graph


Χ2 test
To see if there is a significant difference between the germination of the seeds treated with smoke water and de-ionized water, a Χ2 test was carried out.

Null Hypothesis: Smoke water does not affect germination of gumnut seeds

Alternative Hypothesis: Smoke water affects germination of gumnut seeds



  Smoke water De-ionized water Row total
Germinated 88 49 137
Not germinated 12 51 63
Column total 100 100 200








Proportion of seed germinating = 137/200 = 68.5%
Proportion of seeds not germinating = 100 – 68.5 = 31.5%

Expected number of smoke water treated seeds to germinate = 68.5% of 100 = 68.5
Expected number of de-ionised water treated seeds to germinate = 68.5% of 100 = 68.5
Expected number of smoke water treated seeds not to germination = 31.5% of 100 = 31.5
Expected number of de-ionised water treated seeds not to germinate = 31.5% of 100 = 31.5



Difference Positive
88 68.5 19.5 19.5 5.55
49 68.5 -19.5 19.5 5.55
12 31.5 -19.5 19.5 12.07
51 31.5 19.5 19.5 12.07














Number of degrees of freedom = (rows – 1) x (columns – 1) = (2-1) x (2-1) = 1

Χ2crit = 3.84 for p=0.05


[Comment]: Data processing can be followed.

Since the test value for Χ2calc = 35.25 is a lot greater than the critical value Χ2crit = 3.84 we must reject the Null Hypothesis and accept the Alternative Hypothesis. The test value is significant for p < 0.001

[Comment]: Processed data correctly interpreted

[Comment]: Successful data analysis completed. The conclusion can be deduced.


The effect of smoke water and de-ionized water on post-germination growth
This section of the experiment is designed to test the effectiveness of gumnut seed germination, depending on the type of water it received, either de-ionized or smoke water. Effectiveness was determined by the height of the seedling that emerged from the seed coat of the germinated gumnut seeds. The higher the seedling the more effective the water is on germination. The raw data is presented in appendix A.

[Comment]: Terminology is imprecise here. Strictly speaking, this is post-germination growth



Height of seedlings for germinated seeds

[Comment]: Data table set in context. Clear, unambiguous presentation. Processing can be followed, a worked an example is not expected here. Processing can be followed. Correct
conventions for uncertainties

Water Type


Trial average of
seedling height /mm


Overall average height
/mm ±0.5mm

Overall standard






















On the first observation of the processed data, it can be seen that smoked water has a higher average seedling height than the de-ionized water whilst also having a lower standard deviation. This indicated that the smoked water seeds seedling grew higher than the de-ionized water. The error bars in the graph below suggest that there may be a significant difference between the effects of the treatment on seedling growth. However, the range of variation in the results as given by the standard deviations is large especially for the deionized water treatment trials. To verify this, a t-test was carried out on the data.





[Comment]: The candidate considers the reliability of the data though it could be argued that ungerminated seeds should not be included here. These results (0cm growth) skew the distribution so that it is not normally distributed.

























[Comment]: Appropriate method of analysis chosen.

To statistically test whether the shoot of smoke water germinated gumnut seedlings grew more than the de-ionized water, a two-tailed t-test for independent samples was carried out to investigate whether there is a significant difference between the growth of the seedlings.

Null Hypothesis - the smoke water does not affect the post-germination growth of the gumnut seedlings.

Alternative Hypothesis - the smoke water does affect the post-germination growth of the gumnut seedlings.

t-test formula:

degrees of freedom = n1 + n2 – 1 = 198                    
tcalc = 17.4
tcrit (p=0.05) = 1.97

 Because our test t value tcalc = 17.4 is greater than the critical value tcrit =1.97 at p = 0.05, we can accept the alternative hypothesis, that the smoke water significantly stimulates the growth of the gumnut seedlings germinated. The test value is significant for p < 0.001

[Comment]: Processing can be followed.                                                                                                                                 

[Comment]: Successful data analysis and interpretation completed


Evaluation of Weaknesses with suggested improvements

[Comment]: Student considers the reliability of the data and considers the impact of experimental uncertainty

The potting mixture used was obtained from the local garden shop, and whilst the same brand and the same amount of the potting mixture was used for both seeds in the experiment, the potting mixture may have contained impurities which could potentially have enhanced or reduced the ability of the seeds to germinate, especially because the Yates brand "Contains trace elements to add extra vital nutrients"2  Some of the chemicals from the smoke water also could have potentially rendered them useless, however, the seeds watered with de-ionized water may not have had this potential problem. To improve this, I could have used different support for the seeds such as cotton wool or filter paper. 

[Comment]: Sensible suggested an improvement.

Using different types of leaves, twigs and hay to create the smoke water would give you different chemicals, as each has a differing composition of chemicals, some of which may be beneficial for germination, and some of which wouldn't. For this experiment, I could have used only one variable like hay, instead of twigs and leaves as well. This would narrow my scope of results down as well and I would potentially be able to pinpoint the specific chemical, or source of the chemical, that allows gumnuts to germinate successfully. It may be found that twigs, for example, don't enhance seed germination but leaves do. By singling out the element that best enhances seed germination, further experiments could be carried out, and the exact chemical could be identified, that best enhances the seeds germination.

[Comment]: Feasible extension proposed.

Combined with this, I could have used gumnut seeds that were all the same weight rather than the same size in diameter. I tried to use gumnut seeds that were only 2.00mm in diameter, however, it would have been better served to use seeds that all had a constant weight of 0.2g for example, as then I could have assumed that each seed contained the same amounts and composition of nutrients, enzymes and other chemicals inside it.

[Comment]: Suggested improvement impractical

[Comment]: Unsafe assumption

To further narrow my scope of the experiment, I could have tested the effects of different concentrations of the smoke water as well. Instead of only using a 1:10 ratio of 1 part twigs, hay and leaves to 10 parts deionized water, I could have tested a ratio of 1:5 with 1 part twigs, hay and leaves and 5 parts deionized water. Working out the optimum concentration of smoke water would help this experiment as better and clearer results could be obtained.


[Comment]: Feasible extension proposed.



In conclusion, the experiment supported my hypothesis that smoke water will successfully germinate more Eucalyptus pilularis than de-ionized water. Furthermore, the subsequent growth of the Eucalyptus pilularis seeds by the smoke water was found to be more effective than the de-ionized water due to the significantly taller seedlings of the Eucalyptus pilularis that were exposed to the smoke water. This could because the various chemicals, such as phosphorous and nitrogenous compounds found in the smoky remnants of the burnt organic matter (in my case, the burnt leaves, hay, and twigs) acted as chemical triggers for the E. pilularis to begin its germination out of its dormant state and stimulate its subsequent growth. While all of the active compounds in smoke have not yet been identified, a large majority of the compounds present in the smoke water mixture (NaN03, KN03, NH4CI, and NH4N03) are water-soluble, thus they are easily able to be taken in by the gumnut seed and, once, inside the seed, they are used as these so-called "chemical triggers” to start germination. These chemical triggers work by altering the levels of chemicals that the seed maintains in homeostasis, once the seed has registered these differing levels of phosphorous and nitrogenous compounds, it stimulates the germination of the seed. There are, however, compounds called butenolides that have confirmed germination-promoting action. These butenolides are produced by some plants on exposure to high temperatures and smoke caused by bush fires. In particular, botanists Flematti, Ghisalberti, Dixon and Trengove isolated a particular butenolide called 3-

[Comment]: Compare to relevant scientific theory

methyl-2H-furo[2,3-c]pyran-2-one, which was found to trigger seed germination in plants whose reproduction is fire-dependent, such as the E. pilularis used in my experiment3. One theory about how this butenolide called 3- methyl-2tf-furo[2,3-c]pyran-2-one is formed by the plant is given to us by Light, Berger, and van Steden,

who hypothesized that this particular butenolide was created from cellulose within the plant, and this substance, created by the cellulose, stimulated the seeds

reproductive cycle, and hence, germination4. The two pie graphs that show the percentage of seeds germinated for the smoke water experiment and de-ionized

water experiments respectively, furthermore indicate that my hypothesis was correct, with 88% of the smoke watered seeds successfully germinating compared to only 47% of the de-ionized water seeds germinating. This was backed up with my χ2 -a test that accurately concluded that we could reject the null hypothesis, with a 95% degree of confidence, that the smoke water successfully germinated more seeds that the de-ionized water. The t-test on the seedling growth shows that the smoke water has a  significant positive effect on the gumnut seedlings.

[Comment]: Successful interpretation of the results. The relevant justified conclusion is drawn


Appendix A - raw data tables

[Comment]: Raw data recorded includes uncertainties

                                Seeds watered with Smoke Water (Trial 1)

Seed Number Did the seed Germinate Height of seedling in / mm ±0.5mm
1 Yes 56.0
2 Yes 71.0
3 Yes 73.0
4 Yes 67.0
5 Yes 54.0
6 No


[Comment]: Decimal places should be consistent

7 Yes 58.0
8 Yes 70.0
9 Yes 66.0
10 Yes 61.0
11 Yes 64.0
12 Yes 71.0
13 No 0
14 No 0
15 Yes 59.0
16 Yes 67.0
17 Yes 58.0
18 Yes 63.0
19 Yes 62.0
20 Yes 64.0
21 Yes 72.0
22 Yes 75.0
23 No 0.0
24 Yes 68.0
25 Yes 64.0
26 Yes 69.0
27 Yes 70.0
28 No 0
29 Yes 52.0
30 No 0
31 Yes 79.0
32 Yes 81.0
33 Yes 83.0
34 Yes 74.0
35 Yes 74.0
36 Yes 78.0
37 Yes 63.0
38 Yes 69.0
39 Yes 58.0
40 Yes 70.0
41 Yes 68.0
42 Yes 62.0
43 Yes 63.0
44 Yes 68.0
45 Yes 58.0
46 Yes 81.0
47 Yes 68.0
48 Yes 73.0
49 Yes 67.0
50 No 0









Seeds watered with De-ionized water (Trial 1 )


Seed Number Did the seed Germinate Height of seedling in / mm ±0.5mm
1 Yes 18
2 Yes 27.0
3 Yes 19.0
4 No 0
5 No 0
6 No 0
7 Yes 24.0
8 No 0
9 Yes 25.0
10 No 0
11 Yes 28.0
12 No 0
13 No 0
14 Yes 17.0
15 Yes 23.0
16 Yes 0
17 Yes 16.0
18 No 0
19 Yes 26.0
20 Yes 27.0
21 Yes 15.0
22 No 0
23 No 0
24 Yes 27.0
25 No 0
26 Yes 21.0
27 Yes 22.0
28 No 0
29 Yes 27.0
30 Yes 37.0
31 No 0
32 No 0
33 Yes 26.0
34 Yes 31.0
35 No 0
36 No 0
37 Yes 27.0
38 Yes 41.0
39 No 0
40 No 0
41 No 0
42 Yes 25.0
43 No 0
44 Yes 19.0
45 No 0
46 No 0
47 Yes 37.0
48 Yes 22.0
49 No 0
50 Yes 25.0





Seeds watered with Smoke water (Trial 2)


Seed Number Did the seed Germinate Height of seedling in / mm ±0.5mm
1 Yes 72.0
2 Yes 73.0
3 No 0
4 Yes 72.0
5 Yes 57.0
6 Yes 74.0
7 Yes 79.0
8 Yes 62.0
9 Yes 78.0
10 Yes 64.0
11 Yes 72.0
12 Yes 79.0
13 Yes 72.0
14 Yes 57.0
15 Yes 56.0
16 Yes 83.0
17 Yes 63.0
18 No 0
19 Yes 72.0
20 Yes 63.0
21 No 0
22 Yes 58.0
23 Yes 81.0
24 Yes 57.0
25 Yes 62.0
26 No 0
27 Yes 74.0
28 Yes 73.0
29 Yes 83.0
30 Yes 58.0
31 Yes 74.0
32 Yes 57.0
33 Yes 63.0
34 Yes 79.0
35 Yes 60.0
36 Yes 74.0
37 Yes 79.0
38 Yes 57.0
39 Yes 86.0
40 Yes 53.0
41 Yes 56.0
42 Yes 67.0
43 Yes 63.0
44 Yes 68.0
45 Yes 54.0
46 Yes 68.0
47 Yes 68.0
48 No 0
49 Yes 62.0
50 Yes 72.0












Seeds watered with De-Ionized water (Trial 2)

Seed Number Did the seed Germinate Height of seedling in / mm ±0.5mm
1 No 0
2 Yes 26.0
3 Yes 21.0
4 Yes 23.0
5 No 0
6 No 0
7 No 0
8 No 0
9 Yes 31.0
10 No 0
11 Yes 14.0
12 No 0
13 No 0
14 Yes 16.0
15 Yes 18.0
16 No 0
17 No 0
18 No 0
19 Yes 26.0
20 Yes 31.0
21 Yes 25.0
22 No 0
23 No 0
24 Yes 21.0
25 No 0
26 Yes 31.0
27 Yes 26.0
28 No 0
29 Yes 23.0
30 Yes 36.0
31 No 0
32 No 0
33 Yes 14.0
34 Yes 23.0
35 No 0
36 No 0
37 Yes 23.0
38 Yes 27.0
39 No 0
40 No 0
41 No 0
42 Yes 24.0    
43 No 0
44 Yes 45.0
45 No 0
46 No 0
47 Yes 42.0
48 Yes 23.0
49 No 0
50 No 0

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