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Pea Plants Experiment

Name: Meer Tanzina Husain

PB 101- Final Pea Report

Instructor: Dr. Jensen

Date: 19th February '04

Title: The effect of gibberellic acid on pea plants (Pisum sativum).


Pea plants originated from North America; the species that has been used in this experiment are garden peas. It is very important to decide what varieties of plants will be experimented before one actually does the experiment. In this experiment the pea plant is chosen because of its certain natural characteristics. Researchers like Gregor Mendel has used pea plants in many of his experiments because pea plant is an "inbreeder" plant (it is self-fertile) and a "true breeder" (the off-springs will resemble their parents, unless it is artificially fertilized, or cross-bred)" (Kahn, Attoma, Berardinis, Maloron, and Giacobino). Dwarfism is a genetic trait possessed by some peas. It has been discovered that dwarf mutants cannot produce normal quantities of gibberellic acid (GA), as compared to normal cultivars. The question that arises now is whether the deficiency of gibberellic acid is the main reason for preventing the stem elongation in the dwarf cultivars compared to the normal cultivars. The main objective of this experiment is to test the hypothesis that dwarf mutants are short because they dont produce as much GA as normal plants.

Materials and Methods:

The design for the pea experiment described in Plant Biology 101 Recitation Manual was used as the procedure of treating the plants. This experiment on pea plants was prepared in a green house. Normal pea seeds were planted in two quadrants, Q1 and Q3, in a soil-free potting medium. Dwarf seeds were planted in the other two quadrants, Q2 and Q4. One week later, pea plants were found to be grown in all four quadrants. The plants were trimmed to two healthy seedlings out of four per quadrant and these were used to test the hypothesis. These pea plants were treated in the greenhouse for several weeks. Pea plants in Q1 and Q2 were treated with water while the normal plants in Q3 and the dwarf plants in Q4 were treated with gibberellic acid. The plants were treated three times and measured for the next three weeks. Using a scale, the length of the stem was measured from above the ground to the tip of the stem. Measurements were taken in cm. The last measurements of the plants were taken on the fourth week.

Below is the taxonomy of the experimental plants. Pisum sativum is the scientific name of the plant we used in the experiment.

Taxonomic Hierarchy







Plantae  -- plants




Tracheobionta  -- vascular plants




Magnoliophyta  -- angiosperms, flowering plants




Magnoliopsida  -- dicots, dicotyledons
















Pisum L. -- pea




Direct Children:




Pisum sativum ssp. sativum  -- garden pea




Pisum elatius . -- wild pea




Pisum fulvum  -- tawny pea




Pisum sativum  -- garden pea




Pisum syriacum  -- Syrian pea


Water was applied as the treatment control, while gibberellic acid was used as the experimental treatment in this experiment. In this experiment, the plants in Q1 (normal cultivar) and Q2 (mutant cultivar) that were treated with water and did not contain GA were the two controls.

Water (without GA) was applied as a control because it is vital to plants as it carries dissolved nutrients and other important materials to cells, thus providing proper growth to plants. Normal peas were treated with GA so as to ensure that the difference between the outcomes of the main experiment to the outcome of the control comes from nowhere other than from the result of the effect of GA.


Table 1 shows in detail the growth of plants in respect to time. The table shows one week later after the peas were planted, plants in Q1 grew better than the other ones. Q2 and Q3 had almost similar growth and Q4 had the smallest growth before treatment. Only one plant grew in Q4 so none was removed from that quadrant. The plants were treated and one week after the treatment, the plants were found growing very well, Q1 had plants with the greatest heights. Q2 and Q3 also had very good growth. Q4 had two growth patterns this time, one drastically huge compared to the other. The reason of that was because the one plant with small growth was a new one that grew and it was not treated with GA. The plants were treated and measured again twice that week and the final measurement of the plants were taken on the fourth week. Table 2 shows the final results of the mean heights (cm) of the eight pea plant samples for each treatment type. The mean height in Q1 was 32 cm, Q2 was 14 cm, Q3 was 25.75 cm and Q4 was 36 cm. There is a 28% increase in height for the Q4 Dwarf/GA treatment as compared to the Q2 Dwarf/Water control treatment. A 45% decrease in height for the Q3 Normal/GA treatment as compared to the Q1 Normal/Water control treatment is seen from the results. Figure 3 is a table of data recorded using a large population of experimental plants. The averages of means were taken of experimental plants of a whole class. It can be seen from the figure, Q3 had the highest mean of 43.2 cm, Q1 had a mean of 35.5 cm, Q4 had a mean of 35.4 cm and Q2 had the lowest mean of 19.5 cm.

Figure 1 shows the line graphs of the heights of the total eight plants in Q1, Q2, Q3 and Q4, measured in cm. The horizontal axis (abscissa) indicates the days elapsed starting from the first day the plants were treated. The vertical axis (ordinate) indicates the heights in cm. As it is seen from the graph, in the last week of measurement, Q4 and Q1 had very good growth, Q3 had slower growth rate than Q1 or Q4 and Q2 had the least growth. Figure 2 is a bar graph of average total height per treatment in cm using 58 experimental plants; taken from data of Thursday 3:30 section from Figure 3. Figure 4 shows a histogram of the class means for 402 experimental plants. It is more or less the same pattern of increase in height like 58 experimental plants. These means are feasible as they showed that for relatively large populations of experimental plants, Q3 had the highest growth, Q1 and Q4 had very good growth, and Q2 had the lowest growth.


One possible reason for the drastic change in growth of GA treated plants in Q4 was because it was treated with GA, as compared to the plants treated in Q2 (Dwarf) with water; Q4 had about twice the height of Q2.

The data of the Table 2 shows that Q3 (the normal plants treated with GA) had less growth than that of plants in Q1 (normal treated with water). But for a larger population, it was found that Q3 had better growth than Q1. So unless any misinterpretations of the measurements were made, or any other unknown variables could possibly have changed the growth of plants, no exact conclusion could be reached for the reason of growth of the normal plants. The quadrant data that was used for the comparison of the heights of normal plants was Q1 and Q3.

As it is clearly seen from the data in Table 2, the effect of GA is much greater in dwarf plants than that in normal plants. The quadrant data that was used for the comparison of the effect of GA on normal plants and dwarf plants was Q3 and Q4.

The GA treated plants had fewer nodes than that in control plants. Thus the datas above support the hypothesis of this experiment; that is dwarf mutants are short because they do not produce as much GA as normal plants and it is the lack of GA in the dwarf cultivars which is the main variable preventing the stem elongation. The conclusions were based upon the means taken from a large population of experimental plants shown in Figure 3. Means of two plants provide better approximation of one plant and so a better approximation can be reached by using the means of a large population.

From this experiment, it is seen that dwarfism of the pea plants is due to the fact that they cannot produce normal amounts of GA; thus it supports the hypothesis of this experiment.

Proving or disproving a hypothesis means either accepting or rejecting a hypothesis based on the experiment carried out. And it is only then that a hypothesis can be supported by the evidence; a hypothesis can never be completely proven correct but it can be proven incorrect.

Works cited

Paul Kahn, Giuseppe Attoma, Valérie de Berardinis, Vincent Maloron, and Laurent Giacobino. "Mendel's Experiments and Mendel's Law."

Mendel Museum of Genetics. URL: http://www.mendel (Februry 2nd 2004).

Dr. William Jensen, "Plant Biology 101 Recitation Manual".

Plants, People and the Environment. The Ohio State University (2003).