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The Effects Of Genetic Traits On The Growth Patterns Of Pea Plants
by Michael Demchik

One of the things that appears to be absent in most,if not all textbooks is the treatment of one investigative longitudinal topic from start to finish. While it is important to provide a wide variety of examples to illustrate the various concepts of biology, it is probably more important to deal with a single topic from start to finish which illustrate the many major concepts and ideas presented in the plant phase of biology. While I am sure there are those who would debate this issue, this topic is presented with the intent of showing how a single topic can be worked into one phase of biology teaching and the ramifications it has with respect to the content covered.

In the last twenty years whenever I taught general biology to advanced, average or below average students, I have selected a topic which lasts the duration of one semester or the entire year. The selection of the topic usually comes from early discussion with students in a general way without telling them that I am asssessing what might be the best topic to study longitudinally with the current group of students.Occasionally, a topic is repeated from one year to the next but mostly a new topic with a similar base is selected for study. A few topics that have been utilized over the last few years include "The Effects Of Acid Rain On Pissum Savitii","The Effect Of Acid Spray On Geranium Plants", "The Effect of soil pH On The Growth Pattern Of Potates","The Effect Of Acid Rain On Great Northern Beans","The Effects Of Genetic Traits On The Growth Pattern Of Pea Plants. "Our most recent effort has been the last mentioned project during a full year. This project was run during the first semester and a follow up study during the second semester was done with seeds generated from the first semesters growth.

A wide variety of considerations was taken during the onset of the project. Seeds which had the Mendelian characteristics for pure tall plants, with pure green and pure wrinkled seeds were used in the project. Other characteristics were present which included colored or white seed coats, yellow or green pods, which were either constricted or inflated with either axial or terminal flowers but were interspersed among those with the pure characteristics.

A number of pea seeds were soaked over night and when they reached appropriate size they were examined for visible parts. On the exterior the radicle, hilum, and micropyle were visible. When the testa was removed, and the cotyledons separated, the seed revealed the hypocotyl and two folded plumule leaves which were easily separated with a probe. The seeds were tested for starch, simple sugars, fats, and protein by means of IKI, (iodine dissolved in potassium iodide), Benedict solution, Sudan IV and Biuret reagent.

Students were provided standard sized Perti dishes into which they placed several layers of cut paper towels, which were liberally moistened with water. The excess water was poured off and five seeds of the nature described earlier were placed into the petri dish and equally spaced apart. Two petri dishes of five seeds each were used. Five of these were used for planting and the five were used to determine whether there was a difference between the contents of the seeds originally tested and the seedlings produced in this growth. The same four tests used before were used again to make this determination.

The petri dish cap was placed on the base dish and allowed to stand until the following day until the next day to see if more water would have to be added to maintain the original conditions. Seven days of observations followed and each day any changes that occurred were recorded. During this time period discussion took place on how contraols could be establshed for this experiment. The differences bewteen obervatons, inferences, hypotheses and conclusion were made at this time. Practice with these differences in a wide variety of ficticious situations took place as well. During the initial growth of the pea plants daily predictions were made and tested. Germination rate was determined by dividing the number of plants that emerged from the seeds by the total number of seeds, then multiplied by one hundred percent. The germination rate determined for this project was 96.8 %.

During that time a wide variety of changes took place. Each day the plants were watered as needed and in the same manner as the original set up. The hypocotly emerged first as it broke its way through the testa. Shortly thereafter numerous root hairs emerged. The plumule appaeared a few days later and the seedling ws ready to be planted.

Planting took place in a flat containing twenty holding cells. Standard potting soil was used for the planting. Several days later the plants began to emerge. Students who planted their seedlings appropriately marked the portion of the flat and took daily measurements of the height of the plants over a designated time period. The results were plotted on graph paper and the results compared. All students data was averaged by day and plotted against the five pea plants that each group had. This gave the students the opportunity to see the wide variety of progress that frquently comes with growth of this nature.

One of the characeristics of the plants was tallness and pea plants of this nature are usually staked.However, based on the depth of the holding cells in the flat appropriate support could not be established. The flats were moved to a cart which was used for the movement of physics equipment and strings were tied off to the top rack and strung downward to within a short distance of the potting soil. The developing plants soon attached themselves to the strings with the development of tendrils. Initially, the first attachment required a slight testing around the plant. The cart was moveable and allowed for easy movement of the plants placed in the window so that each side of the plant would essentially receive the same intensity of light during the day and when turned every other day, except for weekends. Each alternating weekend the plants were turned as well. Plants were liberally watered as needed.

During this phase of development one of the students noticed the change in direction of the leaves toward the light when the plants were turned around on the cart. Students investigated and found that they could measure the length of time it took for the plants to display phototrophic responses. On the average it took about twenty minutes to turn through ninety degrees. A wide variety of questions surfaced as the project progressed. One of these was "Is the amount of light reasonably consistent from day to day?" The question was answered with a light meter and an average foot candle rating established over time. Another question was asked to determine if it was possible to set up a situation where a plant could be exposed to the same amount of light. After some thought, it was thought that a record turntable with varying speeds could be used to do the work needed. A control was set up just like the other plant. From this point, we were led into the study of auxins in the phototrophic response and other hormones both accelerators and inhibitors.

During the course of development of the pea seeds to maturity, the various types of standard prepared slides on roots, stems, leaves, flowers and buds were examined. This avenue provide an opportunity to have some notion of the type of tissue that might be developing in the on-going project. An option of using a microtome at this point was considered but it was not used for a variety of reasons, none of which will be mentioned here.

As the plants developed, flowers were evident, the first one appearing twenty-seven days after the plants went into the ground and thirty-five days after the pea seeds were prepared for soaking. Within a period of two weeks, twenty flowers emerged. Some were axial and some were terminal. A few of these were removed and the flowers examined for pistils and stamen. The white flower showed why self pollination occurred with pea plants. After a time of continued development and after apparent fertilization, the pods began to develop and some were constricted and some inflated. One yellow pod appeared with one seed inside. The growth of these pods continued until full maturity took place. The first pod appeared on the thirty-ninth day and within two weeks thirteen pods appeared. One student noticed that the first seed to appear was always attached to the center of the pod. This was easily determined because the pods were viewed against the incoming light. The center pea appeared to be larger than all other seeds in all cases. The shadowing effect caused by the incoming light gave the students this information. Once full maturity seemed to be achieved and some of the leaves began to die off, watering stopped and the plants were allowed to dry on the strings.

The dry plants remained for some time, and were then removed and harvested. examination of all the seeds showed them to be green, wrinkled except for one which was yellow wrinkled. The study of genetic characteristics took place during this time period and all Mendelian characteristics were discussed and the standard examination of dominance and recessiveness was studied.Standard treatment of monohybrid and dihybrid characteristics were studied with the Punnett square method with first had knowledge from this project. During the second semesterless time was spent in class directly with this project. During the second semester the seeds went through exactly the same procedure as previously mentioned and the first filial generation was established for critical evalation. During the second semester less time was spent in class directly on the project. Students periodically viewed the project and when something interesting was seen, the class was informed and everyone took a look. Students frequently looked at the progress before and after class as time went on. Any observed change was reported to the class.

Near the end of the project students were asked to respond to the following question."What would you like to investigate about pea plants other than the things we did or discussed, if you were to conduct an activity about it on your own in school?" Included are a few of the questions raised. What effect did the closeness of the plants have on the growth? Since the seeds were seven years old, would there have been a higher germination rate with fresh seeds? How much difference in height would have occurred if the temperature did not drop off after the students left? What effect would different soils have on the pea plants? While there were many more questions raised these represent a reasonable sampling of them. Once these questions were raised, the students got into their small lab groups, decided on which question they would work with and generate a proposal for study using pea plants. The proposals were graded and each member of the group received the same grade. Several reasonably good studies were generated.

Our involvement with these plants was thorough and provided these students with the follow through of the longitudinal study with a reliability aspect built into it. It raised and answered many questions which were supplemented by classroom involvement. It also provided students who never did a science fair project in biology with a group involvement in a full scale project and with the types of questions and observations that might accompany this type of growth. One advantage that this longitudinal study has is that it is supported and tied to textbook content and supported by observed phenomena.

Evaluation through an attitudinal scale and a content test provided strong support for this program.

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