Schematic diagram of the activation of the enzyme amylase and the level of its substrate starch in a germinating seed5.
Temperature Effects
Beans also require a suitable temperature to germinate, one effect that temperature has is to regulate the rate at which enzymes digest their substrate. Temperature affects the kinetic energy at which particles collide. This is particularly important for enzymes, as for them to work they need to come into contact with their substrate in order to digest them into a product. All enzymes have an optimum temperature at which the rate of reaction is at its fastest. Temperature also affects the activation energy of the catalytic reaction, it provides the energy to form bonds and break others needed for the reaction to take place. But temperature can also have an adverse effect. Enzymes and substrates have a thermal stability. If the temperature becomes too high the enzyme can become denatured preventing it from binding to its substrate. If the active site of the enzyme becomes altered digestion of the substrate will cease.
shows the effect of soil temperature on the number of days to emerge from the soil and the percentage of beans germinating.
Shows the Effect of temperature on reaction rate7.
As with most chemical reactions, the rate at which enzyme catalysed reactions take place is increased by temperature. Even increasing the temperature by a few degrees can dramatically increase the speed at which a reaction takes place. However as enzymes are proteins continuously increasing the temperature of a reaction will not exponentially increase the rate at which the reaction takes place. A temperature will eventually be released at which the reaction reaches a maximum and begins to slow down. This point is known as the optimum temperature. Increasing the temperature of the reaction (above the optimum) the enzymes begin to denature, affecting the ability of it to bind to substrate and producing products. This effect is similar to what happens in both humans and plants alike.
In plants temperature effects the rate of chemicals reactions that occur, from the development of the seed to the growth of the plant. The biological activity of plants has a limited range of temperature. This activity is limited to a window of 0˚C to 50˚C, outside of this range plants cannot survive.
Plants show a predicted curve of growth over a range of temperatures; growth is rapid from 0˚C to 15˚C followed by a steady increase above 15˚C to an optimum temperature of around 20˚C to 30˚C. The optimum temperature range is defined as the point at which maximum photosynthesis occurs and normal respiration takes place. Above 35˚C the growth of most vegetable crops declines. With the thermal death of most plants occurring when temperatures reach 50˚C.
At temperatures below the optimum, the rate at which respiration and photosynthesis is decreased. But significantly photosynthesis seems to be significantly more reduced than that of respiration. The lack of photosynthesis means less carbohydrate will be available for the growth of the seed.
Aim
The aim of this study is to determine the effect that temperature has on the germination of broad beans.
Hypotheses
Hypothesis – increasing the temperature will have a significant effect on rate of germination
Null hypothesis – an increase in temperature will have no effect on the rate of germination
Method
The method was carried out as described in the NEC handout
Apparatus
As described in the NEC handout
Risk assessment
There are no significant risks in this experiment.
Variables
Independent variable: The only factor in my experiment that I am going to change is the temperature at which the beans will be incubated.
Dependent variable: Is the rate at which the beans will grow, to do this the roots of the beans will be measured with a ruler to the nearest mm.
Control variable: I will need to keep a number of important factors constant for my results to be very accurate and reliable.
The levels of light will need to be kept constant so that the beans all receive the same treatment and my results will be as precise as possible. The levels of light can be kept constant by putting dark paper around the jars.
The volume of water added to the jars each day will be done at the same time.
Levels of oxygen will need to be kept constant as well in addition to this so that the seed can easily germinate. This will be easy to do as the jars will be left open to allow ventilation. Oxygen is needed in a similar way to water; the seed takes in the oxygen until the seed coat bursts, letting out the root. If the seed is deprived of oxygen then it will take a lot longer for the seed to germinate.
The duration of which the beans are left for should be the same for each dish. If a certain set of beans are left for a lot longer then some anomalous results could appear because the certain set of beans had been given more time to germinate and grow.
The number of beans should be the same in each dish. It wouldn’t directly affect my final results but it will be a lot more easy and fair to compare the beans in each jar and not a selected number of beans.
Place of incubation
3˚C - fridge
14˚C – living room cupboard
20˚C - airing cupboard
25˚C – green house
Results
3˚C
14˚C
20˚C
25˚C
Mean length
(All lengths are in mm)
As you can see from the results there is no growth of the broad beans at 3˚C over the seven day period. At 14˚C there is slow growth of the roots from day 2 which increases through to day 6. After day 6 there seems to be a slowing of growth as compared to the previous day’s growth. From day 1 the maximum amount of growth seen for the broad beans are those grown at 20˚C and 25˚C. At both temperatures there is a rapid growth of the roots but both seem to show a slowing of growth after day 6 of incubation.
A mathematical calculation can be carried out on this experiment to see if there is a correlation between the temperature and one of the readings in the results; transmission or absorbency. If there is then it is possible to accept or reject our original hypothesis. For this calculation I will be using transmission, as it is an easier figure to use being larger, the average data will be applied to the calculation to get a more accurate result. The hypotheses remain the same from the main experiment found earlier in the report.
A graph to show the mean lean of roots as measured from broad beans grown at different temperatures for 7 days.
Data Table: Spearman's Rank Correlation
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Calculate the coefficient (R) using the formula below. The answer will always be between 1.0 (a perfect positive correlation) and -1.0 (a perfect negative correlation).
When written in mathematical notation the Spearman Rank formula looks like this:
Now to put all these values into the formula.
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d² = 0 multiplying this by 6 gives 0
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n=4, therefore n3 – n = 43-4 = 64 – 4 = 60
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R = 1 - (0/60) which gives a value for R:
= 1 - 0
= 1
The R value of 0.94 suggests a fairly strong positive relationship.
A further technique is now required to test the significance of the relationship.
The R value of 1 must be looked up on the Spearman Rank significance table below as follows:
Degrees of freedom = number of pairs -2 = 4-2 = 2
The results show that there is a significance of 5%, therefore there we can say with a confidence of 95% of the hypothesis and we can therefore reject the null hypothesis. There we can say that temperature has a significant effect on the rate of germination.
Conclusion
The above result supports my original hypothesis and so gives a 95% probability to reject the null hypothesis. This shows that there is a very strong positive relationship between temperature and the germination of broad beans.
Discussion
The results show that there is a significant correlation between temperature and the rate at which germination proceeds. It also showed that at least with the results I have obtained that the optimum temperature for growth of broad beans is somewhere in the region of 25°C. This is evident in the graph produced from the data. Firstly between 6 and 7 days the gradient of the graph seems to tapering off. Also the difference between the lines of best fit for broad beans grown at 20°C is close to that of beans grown at 25°C. All this suggests that 25°C is very close to the optimum temperature for germination. This is shown by gardening advice “Cover the seed and place the tray in a propagator or warm place to maintain an optimum temperature of 70-75F (20-25C)”6.
The results do clearly show that there is a correlation between the temperature of the environment and the rate of germination. This is probably due to the rate at which the enzymes produced after the imbibition of water into the seed. As the temperature increases so does the kinetic energy of both the substrate and the enzyme. This leads to a greater number of collisions between the two resulting in more substrate being produced. The rate at which the substrate (in this case glucose) is produced is going to be the rate determining step. As this provides the energy source to produce ATP through respiration. This is evident by the increase in the slopes of the lines from the data as the temperature increases.
One interesting side note to this experiment is global warming and its affect on plant growth. Currently the average temperature of the plant has risen by approximately 0.8°C over the last century. This means that the rate at which plants will germinate will be affected. This affect could be two fold; either it is a positive effect were germination will take place at a faster rate or conversely it will be reduced. If the temperature of the plant continues to rise at some point the temperature of the soil will get to a value where the enzymes of some beans are adversely affected. For some species it will provide an added advantage and allow it to germinate earlier in the season, this will mean that it more genetically fit. These species will then be more able to compete for space and resources, preventing others from developing. This will then lead to difference in the distribution of some species of plants.
Evaluation
Although this experiment does shows a correlation between the temperature of the environment and the rate of germination of beans it is very limited. All this experiment shows is that as you increase the temperature the rate of germination increases. It does not show the adverse effects that temperature can have such as would occur at extremely high temperatures. It would be obvious to assume that if we kept increasing the temperature that germination would not continue proportionally. At some point the temperature would get to a level where the enzymes involved are denatured due to the heat. This would mean that they would no longer be able to bind to their substrate and therefore not be able to produce the substrates needed for growth. This experiment does not show that and therefore only a limited conclusion can be made as to the effect of temperature. To improve the results incubation of the beans needed to occur at a temperature range over 30°C. This would then have allowed a more accurate optimum temperature for broad beans to be identified.
Although all precautions where taken to reduce fluctuations in the temperature at which the broad beans were incubated. It is obvious to suggest that the temperature of each of these
Although temperature is a significant factor in the growth of beans, there are other abiotic factors that limit seed growth; water, oxygen, light and space. Although the effect of these factors was limited there is nothing to suggest that they could have affected the results. It would have been interesting to set up a control in this experiment where water was not added to the beans on the first day, to see what effect this would have had.
A further experiment could have been carried out to determine what effect rationing water would have had on the beans. This could have been done by keeping the beans at a particular temperature a removing the supply of water after 1, 2, 3 … and up to 10 days. This would have shown when water stops becoming the limiting step.
I would also like to determine the affect that light intensity has on the rate of germination of seeds. In this experiment the seeds where placed in different places and it is evident that some of the seeds may have been in light longer than others. I would like to determine if germination at a constant temperature is affected by the intensity of light. This could be achieved by using polyethylene networks over the light source to produce different light intensities of 100, 50 and 25%.
Bibliography
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Bewley, J.D. (1997). Seed germination and dormancy. Plant Cell 9, 1055-1066.
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Karssen, C., Brinkhorst-van der Swan, D., Breekland, A., and Koornneef, M.(1983). Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L.) Heynh. . Planta 157, 158-165.
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Gibberellic acid-induced secretion of hydrolases in barley aleurone layers and Plant Cell Physiol (1976) 17 (1): 63-71.
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Quail, P.H., Boylan, M.T., Parks, B.M., Short, T.W., Xu, Y., and Wagner, D. (1995). Phytochromes: photosensory perception and signal transduction. Science 268, 675-680
- Solomon, Berg, Martin, Villie, Biology, p. 768.
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Working with Enzymes David Skrincosky, Cindy Santangelo
UCI 205340050507X Candidate Number 0507NEC student number SS121598
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