The Effect of Temperature on the Speed of Response of Dionaea muscipula

Page of J.D. Whitehill

AIM:

The aim of this experiment is to establish whether a relationship between temperature and response times of Venus Flytraps exists.

ABSTRACT:

The idea for this experiment evolved from doing various readings about nastic movements within plants. However, upon investigation, it was discovered that the Venus Flytrap would be better suited to doing studies on response times as the nastic plants required were not available in Queensland. Dionaea muscipula, common name Venus Flytraps, were placed in various temperatures and artificially stimulated, through the use of human hair, to respond. Five Venus Flytraps were bought, each of which had many small, trigger able traps. The size of the trap indicates whether the trap is able to be triggered or not. The reason for this is covered in the discussion section. One trap from each plant was set off at each of the following temperatures: 20˚C, 25˚C, 30˚C and 40˚C. Each of the times were recorded in a table similar to Figure 1.

HYPOTHESIS:

Due to the catalysing effect of temperature on most chemical reactions, it is foreseeable that the Venus flytrap will close faster when placed in a higher temperature.

APPARATUS:

5 Venus Flytraps (each with at least 4 open, trigger able traps)
Thermometer
Stop Watch
Human Hair
Heat Lights

PROCESS:

All 5 VFT’s were placed in an environment which had a temperature of 20˚C and left for 15 mins to allow the VFT to acclimatise.
One VFT was triggered through twice-touching the human hair on the trigger hair located on the inside of the leaf. The period of movement of the VFT from the second touch of the hair until the initial movement of the VFT is completed was timed and recorded in seconds.
Step 2) was repeated another four times using different Venus Flytraps each time. The two extreme times were disregarded and the remaining three time figures were averaged. This was then recorded.
The VFT’s were then placed into an environment in which the temperature was 25˚C. The VFT’s were left for 15 mins for acclimatisation purposes.
Steps 2) and 3) were repeated.
The VFT’s were then placed into an environment in which the temperature was 30˚C. The VFT’s were left 15 mins for acclimatisation.
Steps 2) and 3) were repeated.
The VFT’s were placed into an environment in which the temperature was 40˚C and left for 15 mins to allow them to acclimatise. This temperature is acheived through the use of heat lights.
Steps 2) and 3) were repeated.
All results were assembled and tabulated into Figure 1.

RESULTS:

Figure 1 The Effect of Temperature on the Response time of VFT’s

Figure 2 Graph showing the Effect of Temperature on the Response Time of VFT”s.

DISCUSSION OF RESULTS:

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RESULTS:

Figure 1 The Effect of Temperature on the Response time of VFT’s

Figure 2 Graph showing the Effect of Temperature on the Response Time of VFT”s.

DISCUSSION OF RESULTS:

Studies of the Dionaea muscipula, or as it is more commonly known, the Venus Flytrap were originally carried out by Charles Darwin. Darwin realised that the carnivorous plants can respond to touch in a similar fashion to animals, but as it did not have a nervous system like that of animals, he could not understand how. He also discovered that the plant operated on a double-touch mechanism. Another prominent VFT scientist hypothesises that this double-touch mechanism is in place to prevent artificial stimulation by rain-drops or particles moved by the wind. John Burdon-Sanderson followed Darwin’s progress before testing whether there was a wave of electrical activity (like a nerve impulse produced by animal neurons) set off upon the activation of a trigger hair. He tested this through placing electrodes on the surface of the lobes of the traps and sure enough his hypothesis had been correct.

In animals, the nervous system operates by action potentials being transferred across the synapse by neurotransmitters (like little boats), once they have reached the end of the nerve fibres. The neurotransmitters trigger an electrical response in the neuron opposite. This transfer allows for a wide range of movements to be performed by the animal.

After extensive research by Paul Simons (1992), it was discovered that the action potentials of plants travel through ordinary cells by means of microscopic membrane pores called plasmodesmata. Animal cells can pass action potentials through in a similar fashion; the pores which allow this to occur are called gap junctions. However, these gap junctions are only used when only one type of movement is required in a particular area. The main difference between animal and plants response is that plasmodesmata can only allow action potentials to travel one way and thus, only one type of movement is possible; in Venus Flytraps, this movement is the closing of the trap.

Simons discovered that the actual action potential produced in VFT’s is produced through an influx of calcium ions within the trigger hair. This differs from the action potentials of neurons as they are produced by sodium, not calcium. The influx in calcium ions also initiates an efflux of potassium (K+) and chloride (Cl-) ions which are integral in sustaining the action potential as it travels from pore to pore at a speed of approximately 10cm/second. This speed is sustained by the potassium and chloride ions. As calcium, chloride and potassium are charged particles, their movement across cellular membranes generates a depolarisation signal.

Using these discoveries by Simons, Lauren Legendre investigated how these action potentials made the trap close. He discovered that the movement is actually a result of a rapid growth of the cells on the outer surface and, as he states during his presentation on “The Mechanisms of Trap Closure in Dionaea Muscipula”, “as the size of the cells on the inner surface do not increase their size, the trap will close, the curvature of the trap being greater at the edge.”

Legendre discovered that the actual growth is a result of acidification outside the outer cell layers. This is known as the acid growth theory. “This acidification loosens their cell wall fibres so that the cells will elongate due to their internal turgor pressure.” As this is irreversible, the only way a trap can reopen is through the elongation of the cells on the inner side of the trap. This means that each time a trap is set off, it must grow to reopen and this growth of the fibres in the cell wall prevents the plant from having an infinite ability to close the traps. The actual number of times a trap can close varies between 3 and 12. After the trap has closed too many times, it becomes a regular plant which receives energy from photosynthesis.

According to the results from the experiment, it is unable to discount the marked difference between the times taken at different temperatures. It is quite clear that the lowest temperature (20˚C) produces the slowest response time, and that the highest temperature (40˚C) produces the fastest response time. Human error is a possible flaw in this experiment. The actual point in time at which the trap is deemed to have finished closing is highly subjective and, even then, the reflexes of the tester also may alter the true results. The risk of this was partially rectified through the disregarding of the two extreme times for each temperature when calculating the average.

Another possible error within this experiment is that it is impossible to determine the actual size of the leaves being triggered. Despite attempts to use plants with similar sized traps, this may have affected results but the disregarding of the two extremes should have countered this sufficiently.

After taking all the above information into account, there are only a few possible reasons for the results provided in Figure 1. These include:

The increase in temperature has allowed for the action potential to move faster through the plasmodesmata than what is possible in lower temperatures.
The increase in temperature has allowed the acidification of the cells in the outer layer to be performed faster than what is possible at lower temperatures.
The increase in temperature has allowed for a faster influx of calcium ions, thus triggering the action potential faster than what is possible at lower temperatures.
The increase in temperature has allowed the efflux of potassium and chloride ions to be faster than what is possible at lower temperatures.
A combination of any or all of the above reasons

The fact that the trap is triggered by one touch when the temperature is above 40˚C may be a contributing factor to the actual reason. This may be a result of the overall catalysing effect of temperature on chemical reactions and thus, the most likely answer is a combination of c) and d). However, as there are no studies into this directly, it is impossible for a correct final answer to be given at this stage. Further research into acidification and plasmodesmata should be conducted to provide a direct result to this experiment.

CONCLUSION:

The hypothesis that the plant would respond faster in higher temperatures, proved to be correct. However, whether the catalysing effect of heat on chemical reactions was the only reason for this, could not be established. The history of the Venus Flytraps used may have affected the results. However, the exclusion of the two extreme times from the average means that a fairly accurate time was recorded.

BIBLIOGRAPHY:

Legendre, Laurent “Mechanisms of Trap Closure in Dionaea muscipula”

. Accessed 21-4-02.

Meeker-O’Connell, Ann. “How Venus Flytraps Work” . Accessed 21-4-02.

Otto, J.H. and Towle, A. 1969. “The Leaf and its Functions” Modern Biology. Holt, Rinehart and Winston Inc., New York.

Simons, Paul. 1992, “The Secret Feelings of Plants” New Scientist Magazine - issue of October 1992. Available from:

“The Mysterious Venus’ Flytrap” . Accessed: 21-4-02

“Venus Flytrap” Microsoft Encarta Encyclopaedia 2000.