Introduction: The purpose of the lab is to compare by using a regular T-test two plant species that are present in the forest at the ACS campus and to determine whether they are similar of different. In order to accomplish that, the quantitive data of one biotic and one abiotic factor for five individuals of each of the two species will be compared.
Question: Are two plant species that grow at the forest on ACS campus different or similar in respect to the biotic and abiotic conditions under which they live, and to the qualitative characteristics of their leaves?
Hypothesis: The abiotic factors of these two plant species will be proven similar by the T-test with a P factor greater than 0.05, and the biotic ones will also be insignificantly different with the P factor greater than 0.05, which would mean that the two plant species are not significantly different in terms of the environment where they live. Their outer characteristics will show that their structure is significantly different which would mean that the two plants species are different even though their populations are growing in a very similar environment.
Variables: The independent variables are the 5 individual plants from every species that will be observed in order to collect data. The data would represent the dependent variables is:
· The pH of the soil where each plant is grown
· The maximum length of a leaf of each plant
· The number of other plants that grow within a 20 cm radius of where the root of each plant is in the ground.
Materials:
· Ruler
· Scales
· Distilled water
· Beaker
· Desk
· Litmust paper
· Knife
· Pen
· Paper
Procedure:
1. Choose two plant species that grow in the forest at the ACS campus.
2. Draw a sketch of how the leaf looks like for 1 leaf for every species.
3. Locate 5 individuals of each species that will be observed.
4. For every individual, measure the maximum length of its leaf in cm with the ruler. Record.
5. Using the ruler, locate a circle with radius 20 cm, its center is the plant’s stem.
6. Count the number of plant species that are growing within the located circle.
7. Record.
8. Take approximately 5 ml of soil near the stem of the plant with the knife.
9. Place it in the beaker.
10. Add about 10 ml of distilled water to the soil sample.
11. Stir the soil with water and wait 30 seconds.
12. Wet the litmust paper with the water from the beaker.
13. Wait a little to let it dry.
14. Compare the litmust paper’s color to the color scale that is in the box of the paper.
15. Decide on the pH of the soil and record it.
16. Clean the beaker and the knife.
17. Repeat these steps for every individual plant that is chosen.
18. Locate its place on the map.
Data:
Species 1:
Description:
It has triangularly shaped leaves with light to medium green color. Its edges appear “sharp” and they seem like they are “cut” – they are not smooth. The leaves are usually 3, attached to each end of a branch. Only the 1st one is attached with a stem – the next too are directly attached without a stem to the branch. The “veins” of the leaf are many in number and very visible. They are deep, darker, and easy to spot. They cross the entire surface of each leaf. Leaves attached on a single branch often differ in size, the 1st being the largest.
Drawing: see attached
species 1 | #1 | #2 | #3 | #4 | #5 |
leaf length in cm (+/- 0.05) | 8 | 11.6 | 10.3 | 7.5 | 8 |
pH of soil | 6 | 6 | 5.5 | 6 | 6 |
# of plants within a 20 cm of radius | 3 | 5 | 4 | 3 | 2 |
Species 2:
Drawing: see attached
Description:
It has thin oval leaves with light green color. Many leaves are attached to a single small branch via stems. The leaves are “satin like” with no chine. They have very thin and gentle “veins” that are few in number. Al leaves attached on a stem are roughly the same size. The edge of each leaf is soft and not crisped – instead, it is absolutely round and very thin.
species 2 | #1 | #2 | #3 | #4 | #5 |
leaf length in cm (+/- 0.05) | 4.4 | 5 | 5.5 | 4.2 | 4 |
pH of soil | 6.5 | 6 | 6 | 6 | 6 |
# of plants within a 20 cm of radius | 6 | 8 | 7 | 4 | 4 |
Analysis:
pH of Soil T-test (abiotic):
Number of Plants T-test(biotic):
t-Test: Two-Sample Assuming Unequal Variances | ||
6 | 6.5 | |
Mean | 5.875 | 6 |
Variance | 0.0625 | 0 |
Observations | 4 | 4 |
Hypothesized Mean Difference | 0 | |
df | 3 | |
t Stat | -1 | |
P(T<=t) one-tail | 0.195501109 | |
t Critical one-tail | 2.353363435 | |
P(T<=t) two-tail | 0.391002218 | |
t Critical two-tail | 3.182446305 | |
t-Test: Two-Sample Assuming Unequal Variances | ||
3 | 6 | |
Mean | 3.5 | 5.75 |
Variance | 1.66666667 | 4.25 |
Observations | 4 | 4 |
Hypothesized Mean Difference | 0 | |
df | 5 | |
t Stat | -1.8500095 | |
P(T<=t) one-tail | 0.06177361 | |
t Critical one-tail | 2.01504837 | |
P(T<=t) two-tail | 0.12354721 | |
t Critical two-tail | 2.57058183 | |
The T-test for the pH of soil factor showed that the P factor was 0.39, which is greatly larger than P=0.05. If P is smaller than 0.05 this means that the two samples that have been compared are very different. Therefore, in this case the comparison of the abiotic data for the two plant species proved that in that aspect the two species are growing in very similar environment.
The T-test that compared the number of other plants that lived near the two species that were observed also showed similarity between them. The P factor was 0.12, again larger than 0.05, which meant that the two species are insignificantly different in terms of this biotic characteristic.
The background data collected qualitative information about how a leaf of each of the two species looked like in terms of its shape, color, edge, thickness of the leaf, how and how many of the leaves are attached to a branch, what the leaf’s “veins” look like, and do individual leaves on a single plant differ in size. The following table explains these differences:
SPECIES 1 | SPECIES 2 |
triangularly shaped leaves | thin oval leaves |
light to medium green color | light green color |
edges appear “sharp” and “cut-like” | edge is soft and absolutely round, they are “satin like” with no chine |
medium thick leaves | very thin leaves |
leaves - usually 3, attached to each end of a branch | many leaves are attached to a single small branch |
Only the 1st one is attached with a stem | all leaves are attached with a stem |
“veins” of the leaf are many in number, very visible, deep, darker, cross the entire surface of each leaf. | very thin and gentle “veins” that are few in number |
Leaves attached on a single branch often differ in size, the 1st being the largest. | Al leaves attached on a stem are roughly the same size. |
Conclusion and Evaluation:
The results of the two T-tests showed that the two populations that were observed were statically similar because their abiotic and biotic living factors are similar. This is a result of the fact that the plants that were observed are growing within a radius of no more than 200 meters. It is expected that on such a small area the pH of the soil would not be significantly different, and also other plants living in that area would be more or less equally distributed on it.
The background observation that collected qualitative data about how the leaf of each individual looked like, on the other hand, points that the two populations are indeed different from one another because their outer characteristics show a very different structure in the leaves. The leaves were similar in color, but all of their other quantitive characteristics differed, which points the conclusion that the two species are indeed different, even though the T-test proved that they lived in insignificantly different environment.
This experiment proved that the two populations of the different species lived in very similar environment. This supports the thesis and is a result of that the observed plants lived in a restricted area with radius, no larger than 200 m. The hypothesis was further supported by the fact that the two individuals had very different leaves in terms of structure. This means that although they were place in equal environment, these plants were not created equal in terms of structure.
Sources of error:
There are several possible sources of error in this experiment.
First of all, the method of checking pH of soil is not too accurate because the pH was determined by comparing the paper color to that of the color key and sometimes it was difficult to choose from two bordering options. This is where estimations took place and this may have lead to inaccurateness in the collected data. In order to prevent this in following experiments I would look for pH paper that shows more different colors according to pH levels and is easier to distinguish.
Another possible source of error is that a soil sample could not always be taken very near the stem of the plant because the 1st plant species had thorny stems. As a compromise, the soil sample was taken as near the stem as possible, but this could have lead to some inaccurateness as well. In order to prevent this in a following experiment I would wear protective gloves, so that thorny plants would not prevent me from taking samples.
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