Discussion page 8
Conclusion page 9
Planning
Problem Statement: What is the effect of the auxin 2,4-dichlorophenoxy acetic acid on the height of pea plants?
Hypothesis: If the pea plants are grown with 2,4-D hormone then they will not grow as fast as the control group of plants because the hormone inhibits growth.
Subjects: pea plants (pisum sativum)
Variables:
Independent: 2,4-D hormone paste
Dependent: height of plants
Controlled: duration of growth
Light source
water
Experimental group: plants with the 2, 4-D hormone
Control group: plants with the control paste
Sample size: 11 control plants and 10 experimental plants
Replication: 1
Materials: plant containers, peas, graduated cylinder, water, soil, artificial light source, metric ruler, hormone paste, control paste
Procedure:
1. Label containers.
2. Fill 2/3 full with soil.
3. Water soil so it is like a damp sponge.
4. Place two peas in each container, about 1 inch deep, and cover with soil.
5. Place under artificial light source.
6. Let grow for two weeks.
7. Keep watered so soil is damp.
8. Measure after two weeks.
9. Apply hormone paste to experimental group and control paste to control group.
10. Let grow another two weeks.
11. Measure plants after each week with the paste.
Safety hazards: There are the usual safety hazards such as cuts from broken glass or slips from spilt water. In this lab attention must be paid when working with the hormone. When applying 2,4- D to the plants a swab should be used to keep the hormone off the skin. Also, when measuring the plants one must watch out to keep skin of off the hormone.
Calculations
The f-test and t-test are used to compare the growth of the control and experimental groups after two weeks with the hormone paste.
F-test: used to determine if the degrees of freedom is correct.
n Sx2 Sx
Control (Low) 11 1.25 1.12
Experimental (High) 10 3.98 2.00
F= (Sx2H/Sx2L)
=3.98/1.25
=3.18 > 3.02 = 9/10
The f test does not pass because the table value (3.02) is less than the value calculated.
Corrected degrees of freedom:
K=(3.98/10)/[(3.98/10)+(1.25/11)]
1/0.07= 13.8
The corrected degrees of freedom are used to find the t- value on the chart.
T-test: compares difference between two means.
T= 2.145
Difference between means:
(8.8cm-8.2cm) + (0.49)^1/2 (2.145)= 2.09
(8.8cm-8.2cm)-(0.49)^1/2 (2.145)= -0.89
[-0.89, 2.09]
0 is in the interval and the hormone does not make a big difference at 95%.
Discussion
The results show that after two weeks with the 2,4-D paste the average height of the experimental plants decreases. The graph shows steady growth of both the experimental and control groups between weeks two and three. After week two the average height of the plants with the control paste is gradually increasing. At this point the experimental group’s average height is decreasing.
The F-test is used to determine if the degrees of freedom is correct. The f test does not pass because the table value is less than the value calculated. 0 is in the interval and the hormone does not make a big difference at 95%.
It was unexpected that after two weeks with the hormone some of the plants from the experimental group were still increasing in height. Perhaps, this is due to the human error in applying the hormone paste to the plants. Also after one week of control paste the control group does not grow as fast as it did before. This could either be because of the paste or that plants were not watered properly.
Conclusion
The purpose of this project was what is the effect of the auxin 2,4-dichlorophenoxy acetic acid on the height of pea plants. To do the experiment containers were filled 2/3 with soil and then two peas are placed in each container about an inch deep. For the next two weeks they receive water and artificial light but no paste yet. They are measured after two weeks and the hormone paste is applied to the experimental group and the control paste to the other half of the plants. After each week with the paste the plants are measured.
After two weeks of no paste the experimental group is at an average of 7.0 cm and at 9.0 cm one week after the hormone is applied. The control group’s growth is just as steady even though their average height is less than the plants with 2, 4-D. Between one week after the paste is applied and two weeks after the paste is applied the control continues to grow. However, they grow at a slower rate. During this same time period the average height of the plants with the hormone paste decreased from the previous time measured. The results do support the hypothesis since two weeks after the hormone is applied the average plant height decreases because growth is being inhibited.
If this experiment were to be done again, it would be better to take measurements more often. Also, it would be the hormone should have been applied to a specific place instead of on both the leaves and stem. Had the experiment gone on during a longer period of time there would be more definite results. The average height of the control group plants would exceed those plants with hormones applied to them. Another thing that should be controlled is the amount of paste applied to each plant. A larger sample size would be beneficial also.
The research is practical in that it provides away to control plant growth by the use of hormones. After learning about the results one could use the auxin 2,4-D to inhibit plant growth. This information could be valuable to botanists and home gardeners. These two groups deal with plants and for them it is essential to understand what affects the growth of plants.
Future research based on this project can study the effects of different concentrations of 2,4- D or the effects of this hormone on various types of plants. Another thing that can be studied is the how the location of where the hormone is applied causes different results.