The mean root length for wheat seeds grown on a growth medium, previously occupied by germinated grass seeds, will be significantly less than those seeds grown on previously unoccupied growth mediums.
Null Hypothesis:
There will be no significant difference in the root length between the two conditions.
Planning
As a result of my preliminary experiment I decided that the best conditions in which to grow my seeds would be to use 5ml of water at room temperature.
Method
The forceps were dipped in ethanol and were then flamed in a Bunsen burner. The droppers were wiped with biocide then rinsed with distilled water. The filter paper was exposed to U.V light.
Two layers of filter paper were placed into six petri dishes. 20 grass seeds were placed, in a uniform manner, on the filter paper. 5.0 ml of distilled water was measured in a measuring cylinder and was added to the petri dish via a dropper. The petri dish was then sealed loosely using selotape and labelled with the seed type and date. The petri dishes were then placed on a desk at room temperature.
The grass seeds were watered at three-day intervals. After a period of 1 week the grass seeds were washed using distilled water and the top layer of filter paper was discarded. The bottom layer was used as the top layer, on which the wheat seeds rest in the next part of the experiment.
20 wheat seeds were then placed on the petri dish previously occupied by grass seeds, and were watered every three days, this was repeated in 5 petri dishes. The control group was done at the same time: six more petri dishes were used and only one layer of filter paper was placed in the petri dish and again 20 wheat seeds were placed on top, and watered every three days with 5.0ml of distilled water.
After a period of 1 week the wheat seeds were measured. All the roots and shoots were stretched across a ruler using forceps. The measurements were taken in mm. And the results were recorded in a table.
Apparatus:
- Grass Seeds
- Wheat Seeds
- Petri Dishes- used to control the area of growth for example, the amount of space and water given.
- Filter Paper- 2 pieces of filter paper was used to ensure no debris from the grass roots were left, as the chemicals from decomposition can inhibit the growth of seeds.
- Distilled Water
- Measuring Cylinder- used to accurately measure the volume of water used in each petri dish.
- Ruler
- Selotape
- Forceps
- Dropper- a dropper was used so the arrangement of the seeds were not disturbed. so the seeds had the same amount of space between each other.
- Pens
- Biocide- used to sterilise droppers in order to prevent contamination
- Bunsen Burner
- Ethanol- used to sterilise equipment in order to prevent contamination
The results were recorded by removing each of the seeds and measuring the root and shoot in mm with a ruler and forceps to stretch them across the ruler.
Controls/Variables:
The dependent variable in this investigation is the root and shoot lengths of the seeds. This is dependent on the presence of allelochemicals, the independent variable.
There are various factors that impact the growth of plants that need to be controlled, in order to ensure that the results obtained from the investigation are as accurate as possible.
The volume of water required, will be controlled by using a measuring cylinder, this is important as different volumes of water may affect the rate of growth, low water levels will reduce photosynthesis, inhibiting growth. Therefore the volume of water needs to be the same in each petri dish.
Another factor affecting photosynthesis is heat, thus the temperature to which they are exposed to needs to be the same. High temperatures can cause increased respiration above the rate of photosynthesis. This means that the products of photosynthesis are being used more rapidly then they are being produced. For growth to occur photosynthesis must be greater than respiration. Therefore lower temperatures can result in poor growth. As the petri dishes are placed in a room the temperature may fluctuate therefore the petri dishes must be keep in close proximity of each other.
The same sized petri dishes will be used, also the distance apart from each of the seeds and the sides of the petri dish must be the same. So that each seed has the same amount of space in which to grow and thus compete for the same amount of water and space as each other.
The germinated seeds need to be exposed to the same amount of light, as photosynthesis is light dependant and low light levels may limit the growth.
The seeds will be watered and measured at the same time as the water may be used more at a certain time of day when the rate of photosynthesis is high.
Biocide will be used as any bacteria present in the petri dishes could have affected growth of the seeds, also the bacteria could have affected the way in which the allelochemicals worked. All this could have an impact on the reliability of the investigation. The ethanol used in the investigation was also to prevent contaminating the petri dishes.
The same type of seeds will be used, from the same packet, however individual differences are uncontrollable.
Two layers of filter paper will be used in each petri dish. This will be done because if there was debris left from the roots of the grass, the decomposing plant tissue may release chemicals, which could affect the growth of the wheat seeds.
Safety precautions:
Caution will need to be taken when using the Bunsen burner, it must be used responsibly, never left unattended and when not in use the safety flame should be used.
Ethanol is flammable therefore it should be kept away from the bunsen burner.
Work areas should be kept clean and tidy at all times. Also long hair should be tied back.
Care must be taken when using biocide as it may irritate the skin, wash the effected area immediately with water and do not ingest.
Goggles should be worn, in order to prevent potential harm to the eyes.
Result:
The following table shows the average length of the wheat roots and shoots of the two groups.
Each petri dish contained 20 seeds.
Table 1- Control Group: wheat seeds grown in petri dish.
Table 2- experimental group: Wheat seeds grown in petri dish previously occupied by grass seeds.
Table 3- a comparison between the overall averages of the control group and experiment group and the differences between the two groups.
Graphs:
Graph one
Graph two
Statistical Analysis:
The statistical being used will be the student’s t-test. The t-test is a statistical calculation, which provides a way of measuring the probability that the results occurred in correspondence to my hypothesis, or simply by chance. The values will then be evaluated.
Two t-tests will be used; one to compare the growth of the roots from both groups and the another will compare the shoot length from both groups.
The following formulae is used to calculate ‘T’:
T = ( X1 – X2 )
√ S1² + S2²
n1 n2
X = the mean of the X values
S = the standard deviation
n = the number of seeds
1 = data set number 1
2 = data set number 2
Standard deviation = √Σ(x – x)²
n
The first t-test compares the total growth of the roots of both the experimental group and the control group.
First t-Test: Shoot Results
t= 14.1
sdev= 1.58
degrees of freedom =178
The probability of this result, assuming the null hypothesis, is 0.000
Group A: Number of items= 90
3.00 4.00 4.10 4.10 4.10 4.20 4.20 4.20 4.50 4.60 4.70 4.80 4.90 4.90 5.00 5.00 5.00 5.00 5.00 5.00 5.10 5.10 5.10 5.20 5.20 5.20 5.20 5.20 5.30 5.40 5.40 5.50 5.50 5.50 5.50 5.50 5.60 5.60 5.70 5.80 5.80 5.80 5.80 5.90 5.90 6.00 6.00 6.00 6.10 6.10 6.20 6.20 6.40 6.60 6.60 6.60 6.70 6.70 6.70 6.80 6.80 6.80 6.80 6.90 6.90 6.90 7.00 7.10 7.10 7.20 7.20 7.30 7.40 7.40 7.50 7.50 7.50 7.50 7.70 7.90 7.90 7.90 8.20 8.30 8.60 8.80 8.90 9.20 9.20 9.70
Mean = 6.15
95% confidence interval for Mean: 5.826 thru 6.483
Standard Deviation = 1.36
Hi = 9.70 Low = 3.00
Median = 5.95
Average Absolute Deviation from Median = 1.11
Group B: Number of items= 90
0.200 0.500 0.500 0.700 0.800 1.00 1.00 1.00 1.00 1.20 1.20 1.20 1.30 1.30 1.30 1.40 1.40 1.50 1.50 1.50 1.50 1.70 1.70 1.70 1.80 1.80 1.90 1.90 2.00 2.00 2.00 2.00 2.00 2.10 2.10 2.10 2.10 2.20 2.20 2.20 2.30 2.30 2.50 2.50 2.50 2.50 2.50 2.50 2.60 2.60 2.70 2.70 2.70 2.80 2.90 2.90 3.00 3.00 3.00 3.00 3.00 3.10 3.10 3.10 3.20 3.20 3.20 3.40 3.40 3.50 3.50 3.50 3.50 3.60 3.70 3.90 3.90 4.10 4.80 5.00 6.00 6.20 6.40 6.60 6.90 7.00 7.10 7.50 7.90 8.50
Mean = 2.84
95% confidence interval for Mean: 2.513 thru 3.171
Standard Deviation = 1.77
Hi = 8.50 Low = 0.200
Median = 2.50
Average Absolute Deviation from Median = 1.23
Second t-Test: Roots Results
t= 21.3
sdev= 1.34
degrees of freedom =178
The probability of this result, assuming the null hypothesis, is 0.000
Group A: Number of items= 90
6.80 6.90 6.90 7.00 7.30 7.80 7.80 7.80 7.80 7.90 8.00 8.00 8.00 8.10 8.20 8.20 8.20 8.40 8.40 8.40 8.50 8.50 8.50 8.60 8.70 8.80 8.80 8.90 9.00 9.00 9.00 9.00 9.00 9.00 9.10 9.10 9.20 9.20 9.20 9.20 9.20 9.20 9.30 9.40 9.40 9.50 9.60 9.60 9.60 9.60 9.70 9.80 9.80 9.80 9.90 10.0 10.0 10.1 10.1 10.1 10.1 10.2 10.3 10.3 10.4 10.5 10.7 10.7 10.8 10.8 10.9 11.0 11.1 11.2 11.3 11.3 11.4 11.5 11.5 11.5 11.5 11.7 11.7 11.9 12.2 12.2 12.4 12.5 12.7 12.9
Mean = 9.63
95% confidence interval for Mean: 9.356 thru 9.913
Standard Deviation = 1.45
Hi = 12.9 Low = 6.80
Median = 9.45
Average Absolute Deviation from Median = 1.17
Group B: Number of items= 90
3.20 3.20 3.20 3.40 3.50 3.60 3.70 3.70 3.80 4.00 4.00 4.00 4.10 4.10 4.10 4.10 4.20 4.20 4.20 4.20 4.40 4.40 4.50 4.50 4.50 4.50 4.50 4.50 4.60 4.70 4.70 4.80 4.80 4.80 5.00 5.00 5.00 5.00 5.10 5.10 5.20 5.20 5.20 5.30 5.30 5.30 5.30 5.40 5.50 5.50 5.60 5.80 5.80 5.80 5.80 5.80 5.90 5.90 6.00 6.00 6.00 6.00 6.00 6.00 6.00 6.10 6.20 6.20 6.20 6.30 6.30 6.30 6.50 6.50 6.50 6.50 6.50 6.70 6.70 6.80 7.00 7.00 7.20 7.30 7.50 7.50 7.60 7.90 8.00 8.50
Mean = 5.38
95% confidence interval for Mean: 5.103 thru 5.659
Standard Deviation = 1.21
Hi = 8.50 Low = 3.20
Median = 5.30
Average Absolute Deviation from Median = 1.00
Results of t-test analysis
After calculating a value for T, the figures can be compared.
A difference between two means is significant if the calculated t value is greater than the critical value, which can be found in a critical table.
The degrees of freedom relevant to my sample can be calculated using the following formulae:
DF = n1 + n2 – 2
Therefore if this is applied to my results: both n1 and n2 are equal to 90. Hence the degree of freedom is 178 (90 + 90 – 2 =178).
The t value obtained from my root comparison was 21.3. This value is greater than the critical value of 1.98 (the value at a 0.05 probability at 178 degrees of freedom). This indicates that over 95% of the time, the mean set of data is significantly different. This shows that the data obtained is good enough to support a conclusion with 95% confidence.
The t value obtained from my shoot comparison was 14.1. This value is greater than 1.98, this again indicates that over 95% of the time, the set of data is significantly different. Again this shows the data is good enough to support a conclusion with 95% confidence.
This statistical evidence greatly supports my hypothesis which states that, the mean root length for wheat seeds grown on a growth medium, previously occupied by germinated grass seeds, will be significantly less than those seeds grown on previously unoccupied growth mediums.
Therefore I can reject my null hypothesis.
Analysis:
From graph one it is evident that there is a difference between the two groups. The control groups average root length was longer than the experimental group. The average length for the control group was 100mm compared to 54mm for the experimental group, showing a difference in the groups of 46mm.
From graph two we can see a similar pattern that shoot length of the experimental group was shorter than that of the control group. The average shoot length for the control group was 65mm and for the experimental group it was 31mm, showing a difference of 34mm.
It is also evident from the raw data that the experimental group had more seed that did not germinate than the control group. In the experimental group 27 seeds did not germinate in comparison to 8 in the control group.
Petri dish 6 of the experimental group appears to be an anomaly as the average root and shoot growth is much greater than the 5 petri dishes. This could have been due to the amount of sunlight the seeds were exposed to, as this is one variable that was not controlled.
The error bars show us that the range is quite low therefore the error is fairly low.
In summary it is clear from looking at the graphs that the experimental groups roots and shoot lengths were much shorter than the control group indicating an inhibition of growth.
Conclusion:
From the results of this experiment there is a clear indication that the experimental groups seed growth was affected by allelochemicals present on the filter paper produced by the grass.
The experimental groups in comparison to the control groups showed signs of inhibited root and shoot growth, a sign, which is associated with the effects of allelopathy.
There are several reasons why there was an inhibition of growth. Firstly, the grasses grown secrete allelochemicals (phytotoxins) from their roots into the surrounding area. The roots of the wheat grown absorb these chemicals. The toxins may inhibit the germination of seeds, growth or photosynthesis. Or they may block the absorption of critical nutrients.
The allelochemicals secreted from the grass could have inhibited the enzymatic activity of the amylase in the wheat seed. Amylase is needed to convert starch into sugars, which in turn are used in respiration. If the allelochemicals hinder this activity then the growth of the seed will be inhibited. This could also explain why so many of the experimental group’s seeds did not germinate.
The investigation does have some limitations. Various improvements could be made including, the use of more sensitive equipment, such as a microscope to measure the root and shoot lengths and a micrometer for accuracy. However as a ruler was used an appropriate degree of accuracy was obtained as when measuring in mm whole numbers can only be used.
An incubator could have been used, as it is possible that the temperature could have fluctuated in the room and had an effect on the growth of the seeds. The incubator could have been used to keep a constant temperature.
The anomalous results obtained from petri dish 6 could have been avoided if a UV light was used, as it would have controlled the light exposure to the seeds.
Different plants could be used to investigate the prevalence of allelopathy. Other factors could have been measured such as, the colour of leaves or the amount of metabolism.
My aim was to investigate whether the allelochemicals produced by grass seeds at germination inhibited the growth of wheat seeds. My investigation has shown that it does.
Further investigation:
An experiment could have been conducted to investigate the effect of wheat on allelopathy. In order to determine whether allelopathy can be used as a natural herbicide.
References:
1 Rice, E.L., 1984. Physiological Ecology: A Series of Monographs, Texts, and Treatises. 2nd ed. Florida: Academic Press, inc.
2
3 Thompson, C., 1984. The Chemistry of Allelopathy. Missouri: American Chemical Society.
4
5
6 Rice, E.L., 1979. Bot. Rev. 45.
7
Biology preliminary investigation
Aim: the aim of the investigation is to investigate what conditions the wheat seeds and grass seeds germinate best in, there are two factors which are varied to test the
best conditions for the seeds to germinate.
Rationale: the reason for this experiment is being done is so that the best conditions for the plant to grow can be establishes, so when doing my main experiment the growth of the seeds will not be effected by the conditions they are exposed to. So a cause and affect can be recognised.
Hypothesis:
The seeds will germinate best in the petri dish where the temperature is at room temperature and 5ml of water is used.
Null hypothesis:
There will be no significant difference in the grow of the seeds in different conditions. All the seeds will grow similarly to one and other.
Method:
Eighteen petri dishes were obtained and each one contained a sheet of filter paper. Different concentrations of distilled water were measured in a measuring cylinder and poured carefully into the petri dishes, the concentrations were as follows; 2.5ml; 5.0ml and 10ml. There was 9 petri dishes of wheat seeds and 9 of grass seeds. The seeds were then checked and measurements were taken on the fourth and sixth day. The seeds were watered every 3 days. Measurements were taken by using forceps to stretch the roots along a ruler.
Apparatus:
- Filter Paper
- Wheat seeds
- Grass seeds
- Distilled water
- Forceps
- Selotape
- Petri dishes
- Incubator
- Measuring cylinder
- Marker pen
- Ruler
- Selotape
Controls/Variables
The same amount of water was used each time. The same type of seeds were used from the same packet. The distance the seeds and the sides of the petri dish was the same for each plant, so that each seed had the same amount of space in which to grow. Each seed was grown for the same amount of time
Results:
Grass seeds at 25°C
Grass seeds at 30°C
Grass seeds at Room Temperature
Wheat seeds at 25°C
Wheat seeds at 30°C
Wheat seeds at Room Temperature
Evaluation
There are various factors that impact the growth of plants such as water, temperature sunlight. A plant needs the right amount of all these.
In this experiment the conditions which suited the growth of both the seeds was, room temperature with 5ml of water.
The volume of water required, is important as different volumes of water may affect the rate of growth, low water levels will reduce photosynthesis and therefore the plant will not grow properly. Another factor affecting photosynthesis is heat, thus the temperature to which they are exposed to needs to be right in order for the seeds to grow well. High temperatures can cause increased respiration above the rate of photosynthesis. This means that the products of photosynthesis are being used more rapidly then they are being produced. For growth to occur photosynthesis must be greater than respiration. Therefore lower temperatures can result in poor growth. These factors are important when investigating allelopathy as only the allelopathic effects need to be measured. The hypothesis can be accept and the null hypothesis rejected.
Raw data
Experiment Group
Petri dish 1
Root
Shoot
Petri Dish 2
Roots
Shoots
Petri Dish 3
Roots
Shoots
Petri Dish 4
Roots
Shoots
Petri Dish 5
Roots
Shoots
Petri Dish 6
Roots
Shoots
Control Group
Petri Dish 1
Roots
Shoots
Petri Dish 2
Roots
Shoots
Petri Dish 3
Roots
Shoots
Petri Dish 4
Roots
Shoots
Petri Dish 5
Roots
Shoots
Petri Dish 6
Roots
Shoots
37/40
