Exp. Biology : Kraus Michael Olshan

Period : G Class Nov. 16, 98

 

The Effects Of Temperature On The Germination And Growth Rates Of Radish Seeds

 

Introduction

When seeds of any type are germinated and grown there are numerous factors and variables that must be taken into account. These Variables include amounts of light, amounts of water, amounts of air, and the temperature of the environments in which the seeds are placed in, to name a few. These variables are essential for determining how alterations in a plantís environment can significantly affect natural processes like plant germination and growth from occurring at a natural rate. In an effort to test the effects of different temperature environments on the rate of these two processes in Radish seeds I had to isolate all other variables so that I would know that the results I would achieve, and the data I would collect, would reflect changes based solely on the differences in temperature of the areas in which I placed the seeds.

Many plant seeds are versatile enough to not only germinate and grow in different or less than ideal temperature environments, but can also thrive in more than one type of temperature setting. The experiment which I created to test these effects of temperature on germination and growth, would automatically test whether or not Radish seeds possessed this same versatility. In order to do this I had to limit the number of variables to one, the temperature of the environment in which the seeds would be allowed to remain in. The question I looked to answer was whether or not differences in temperature would effect the germination and growth rates of Radish seeds by either speeding up or slowing down these rates. I proposed that the differences in temperature would in fact have a significant effect on how quickly and successfully Radish seeds would go through germination and then soil growth.

This hypothesis was made due to the fact that we know when certain essential variables, such as temperature, are altered in the development and growth of plants, they determine not only whether or not the plant will have enough to survive, but also whether the plant will thrive . It is a fact that all plants can not grow in any environment and that plants are usually very selective in where and what type of environment they will grow in. This is why we see certain plants growing in different parts of the world with different temperature climates than others. The rate of germination in this experiment has been determined by the weight of the seeds at different intervals, while the rate of growth has been determined by the height of the plant. This was done in order to differentiate between the first growth from the seed and the growth of the plant from a smaller but already developed state.

 

Methods And Materials

In order to perform the experiment and design the experimental setup used to test my hypothesis I had to construct three environments that were identical and held all variables constant except for the temperatures of the three different situations. My experiment compared the germination and growth rates of radish seeds allowed to remain in room temperature ( 28*C ), warm temperature ( 40*C ), and cold temperature ( 11*C ) environments for a period of two weeks in total. The first week contained the germination phase of my experiment and was then followed by the growth phase which took place during the second week. Every effort was made, and rather successfully, to ensure that their was only the one variable of temperature that was not held constant between the three groups of seeds. The following is a chronological and complete set of steps taken in the execution of both the germination and growth parts of my experiment :

Germination Procedures :

1) I first prepared three sterile, large, petri-dishes with a piece of size 8 filter paper, per dish. This paper fit tightly so that there was no gap between the edge of the paper and the edge of the dish.

2) I then labeled each one of the dishes with my name, the class, my teacherís name, the number of seeds in the dish, and the type of seeds in the dish.

3) I then saturated the filter paper pieces in each of the three dishes with 5 ml. of tap water per every four seeds placed into the dishes. The four seeds were then placed with the use of clean tweezers, approx. 3 cm. apart from each other in each dish, to ensure crowding would not become an issue.

4) The three dishes were then sealed shut with two generous pieces of Parafilm per dish, in order to minimize the amt. of water that would be lost due to evaporation.

5) When the dishes were made ready I shifted my attention to preparing the three different temperature environments. The refrigerator was used to hold the dish of seeds being tested in the cold. I, along with Mr.Rieblien, carved a notch out of the door so that when closed it would not trigger the interior light to turn off. I then placed a 60 watt. soft white light in the refrigeratorís light socket and then placed the seeds in a location away from the light where the light meter read 300. A piece of tape was placed over the dish to give my name and my teachers name so that no one would remove the dish at any time.

6) In order to prepare my warm environment I used a heating trey set to a low setting of one and placed a stack of three troughs on top of it. The trough on top of the stack was then filled to the brim with tap water and allowed to come up to a temp. of 40*C. A light containing a bulb identical to that in the cold and room temp. setups was clipped to the side of the trough and turned on. The dishes were then floated on top of the warm water and a metal box made out of a pre-existing box and taped on metal panels was placed over the heating trey. This box simulated the inside of the refrigerator.

7) In order to set up the room temp. environment, I used one of the cabinets immediately under the counter holding the warm temp. setup. This cabinet was metal already and ha d closing door which allowed me to conceal the environment. I placed a light with an identical bulb as the ones used in the warm and cold setups in the cabinet and placed the dish of seeds in the cabinet. Like in the warm and cold temp. environments I placed the dish at a distance where the light meter read 300.

8) The dishes were the allowed to germinate for a week and my observations and data were collected every day of that week along with two sets of detailed drawings made on the second and fifth day of germination. These observations included :

Initial mass, new mass, initial circumference, new circumference, color of seeds, colors of plant parts, number of roots, rate of root growth, the plant part exposed first, and the percent of seeds germinated.

9) The entire above procedure was then replicated for a "Backup," set of seeds that grew literally along side the primary set just in case something were to happen to the real set.

10) Both sets of seeds were re-watered with approx. 2 ml. of tap water per dish per day and the temps. and light readings of the three environments were checked and recorded on my daily maintenance schedules hanging on the cabinet along side my data tables. Figures one through five of my data collection sheets contains these observations and figures eighteen and nineteen contain my daily maintenance schedules.

Growth Procedures :

1) Before starting the growth part of my experiment I had to prepare the cups in which I would be planting and growing the Radish plants in. The cups were first labeled with my name, my teacherís name, my class, and the number of plants placed in the cup. I then filled the cups each with a generic soil and loosely packed the soil before watering with 10 ml. of tap water.

2) After preparing the cups I placed the now germinated seeds in the soil, roots down just under the surface, but deep enough to cover the long white roots.

3) The cups were then placed back in their respective temp. environments and allowed to remain at the same light intensity and temp. as they did while germinating. The cups remained this way for five days.

4) During the course of these five days they were checked for light readings and temp. readings, and also observed so that I could gather and record my daily data and observations. This took five days in total.

5) I placed all the data I had been collecting in my tables which contained the following categories : Color of plant parts, number of leaves, length of leaves, number of flowers, height of plant, days of growth, rate of growth, and percent of growth.

6) Like in the germination procedures, I made two sets of detailed drawings on both the second and fifth day of the growth process.

Materials :

1) 12 standard size radish seeds

2)Three large size petri-dishes

3)Three pieces of filter paper ( Size 8 )

4)A graduated cylinder (20 ml.)

5) A large chemistry heating trey

6) Parafilm

7)Light meter

8)Three 60 watt soft white light bulbs

9)Two clip on light fixtures

10)Six inch ruler

11)Tweezers

12)Labels

13)Metal box

14)Two metal panels

15)Thermometer

16)Duct tape

17)Soil

18)Polaroid camera

19)Computer ( Excel )

20)Wooden box ( To prop up metal box )

 

Results

The data which I have collected and recorded has been split into four major sections. The first is the data collected from the germination and growth part of the experiment and relates to the tables in figures 1-10. The next major part of the data can be found in the graphs provided in figures 11 and 12 which illustrate the weight / day rate of the plant during the germination phase, and the plant height / day for the growth phase. These two graphs contain the rates of both germination and growth. The next major part is found in the detailed drawings made of the germinating seeds and growing plants during their second and fifth days. The next and last major part of the data collection presentation can be found on figures 18 and 19 in which I have attached my daily maintenance schedules along with my T-test results for both germination and growth.

 

The data tables found in Figures 1-10 contain both my observations and mathematical data collected from my germination and growth phases of the experiment. The idea of this table setup was to allow the readers of this lab report to be able to follow a chronological increase in the weight / day or germination rate of the cold and room temp. seeds while noticing a lack of germination from the warm seeds which were germinating at the same time. I also wanted the reader to pay close attention to the height of the plant / day or growth rate of the plants in the growth phase of my experiment. This too should allow the reader to chronologically follow the growth of the plants throughout the week, while observing a lack there of for the warm seeds.

The graphs found in Figures 11-12 are intended to provide the clearest possible visual image of the trends of the germination and growth rates of the three different temp. environments. These graphs allow the reader to see the correlation between time and the two rates being evaluated while also being able to immediately compare the success and rate of the three different temp. seeds. The slope and height of the graphs illustrate the speed at which the seeds germinated and the speed at which the plants grew. The steeper the slope the faster and the more horizontal the line formed, the lower the rate.

The drawings found in Figures 14-17 illustrate literally the progress of the germinating seeds and the progress of the growing seeds. As I said before, these drawings were made on the second and fifth days of the two phases of the experiment. They are drawn to scale, give the magnification, have labeled parts, and are titled and labeled according to the temp. they were kept in. These pictures allow us to clearly see the clearly defined stems, seeds, leaves, and roots of the Radish plants and also allow us to compare the actual appearance of different seeds from the different environments.

The maintenance schedule found in Figures 18-19 pertains to the daily maintenance tasks that I performed daily in order to make sure that no variables were changing as the experiment progressed. This schedule acted as my data table for recording the light intensity readings, temp. readings, watering schedule, and ultimately my T-test results for both germination and growth. The T-test is a way of determining whether or not the differences in your data between the control and all other results is significant and whether it is because of the variable that was altered and tested for.

Discussion

The data I collected showed a clear difference in the rates of both the germination and growth of the Radish seeds in the experiment based on the temp. in which they were allowed to remain. The seeds germinated and grown in the cold and room temp. environments showed both similar germination and growth patterns as well as rates. However, as was expected this was not consistent through out the entire experiment. The seeds germinated in the warm temp. environment never had any success. These seeds failed to germinate and failed to grow. Because the design of the experiment, I feel, was successful in making a conscious effort to keep all variables except temp. constant, I have to infer that the warm temp. was solely responsible for this. The temp. exceeded the maximum temp. at which the Radish seeds could develop and grow successfully. The room and cold temp. environments worked within the Radish seedís limits of what was considered to be a livable environment, and thus had success for the two week period. The results of the warm seeds was not a total loss in any way. In fact, it helped prove my hypothesis rather convincingly. I stated in my hypothesis that I felt that differences in temp. would directly effect the rate of germination and growth, in this case it completely stopped the two processes. This was an obvious effect and one hat allowed my to make convincing contrasts between my three sources of data.

There were certain potential sources of error in this experiment. This experiment was high maintenance in the fact that it required constant checking and readjusting of everything from lights, positions, and water to the setting of the heating trey. In this experiment, if these things were not accounted for, there would have been the introduction of a new variable into the experiment and would have thus discredited its findings. In order to maintain continuity I had to battle evaporation daily to make sure my seeds would not dry out to make sure the seeds in my warm water bath did not literally cook to death.

Unfortunately no one else in the class had done their research on the effects of temp. on either the growth rate or germination rate of a seed. This made it hard for me to compare my work with that of anyone elseís but I can compare it with the germination work we started the year off with. I know that when Radish seeds were germinated at that time they were all germinated in a room temp. environment which was similar to that of the environment I used as my control environment in this experiment. The results were almost identical to those of my control this time which tells me that my procedures and results were in some way consistent and that I had been doing something right.

The data shows that according to my T-test the differences between the germination rates of the three temp. environmentís seeds was significant for cold vs. room temp. seeds but not significant for warm vs. room temp. seeds. As for the growth rate, the T-test shows that the difference between the room vs. warm temp. was significant, while the room vs. cold was borderline significant. This data does show a clear and mathematically supported illustration that Temp. was a determining factor in 75% of the comparisons made and in all of that percent, caused a significant change in the rates being tested.

 

Conclusions

From my experiment I was able to infer and prove that temp. differences do have significant effects on both the germination and growth rates of radish seeds over a two week period. This data has allowed me to see not only how to isolate a variable and test for the effects of that one specific variable on an experiment, but also how to hold all other variables constant. I also came to realize that failure to prove something that contradicts your hypothesis is very much an effective means of proving it. This was an experiment where the failure of a certain member of the group being tested helped to make a point that much clearer. When one speculates that the temp. of an environment causes one seeds to live and grow while another temp. causes an identical seed to remain dormant for two weeks, it is clear to say that temp. does in fact affect the germination and growth rates of radish seeds when all else is held constant.