To investigate the effect of habituation of snails to a stimulus To developed certain experiment skills, such as working safely, producing valid results, recording results and drawing valid conclusions from results. INTRODUCTION The snails Figure 1: Garden snail Taken from http://bugaboo. Bloodspot. Com/2011 /05/handsome-snail. HTML Snails are one of the earliest known types of animals in the world. There is evidence that they evolved more than 600 million years ago. They are able to adapt to a variety of living conditions and they don’t require large amounts of food.
They have been able to continually evolve to survive the conditions around them. Snails belong to a group of animals with a soft body called mollusks which are related to oysters, clams, and other shellfish. Characteristically they have soft, instrumented bodies. Normally, their soft bodies are protected by a hard shell. Garden snail also known as Helix spears. The body of the snail is long, moist and slimy. It has a shell to protect its soft body. The shell of a snail is made up of calcium carbonate. The shell becomes very strong and remains that way as long as the snail consumes a diet that is full of Alicia.
When the snail is disturbed, it simply withdraws or pulls itself back into its shell. The snail also retreats into its shell and seals the entrance in dry weather to protect its body from drying up. A snail is most active at night and on cloudy days. During very cold weather or winter, it hibernates in the ground. Habituation Habituation is a decrease in response to a stimulus after repeated presentations. As a procedure, habituation is the repeated presentation of an eliciting stimulus that results in the decline of the elicited behavior (the process of habituation).
The most interesting thing about habituation is that it can occur at different levels in the nervous system. After a while, sensory systems may stop, sending signals to the brain in response to a continuously present or often-repeated stimulus. The common example of sensory habituation is lack of continued response to strong odors. Habituation to complex stimuli may occur at the level of the brain in which the stimulus is still perceived, but the animal has simply decide to no longer pay attention. Besides, habituation is important in filtering the large amounts of information received from the surrounding environment.
By habituating to less important signals, an animal can focus its attention on the most important features of its environment. Humphrey (1933) was one of the first who studied the process of habituation. He placed a number to snails on a glass plate; nee would then give the plate a sharp Jerk that would cause the snails to react and to withdraw reflexively into their shells. After each Jerk, the number of snails that had withdrawn was counted, it was found that after several trials the number showing withdrawal reflexes decreased and less and less would withdraw into their shells.
Since Humphreys study a variety of techniques have been used to study habituation. For example, there is one of the famous experiments investigating habituation which is involving the giant sea slug Plays. The experiment which is conducted by Care, Pinker and Kendal (1972) found repeated stimulation of the papilla’s siphon causes a reduction in the magnitude of gill withdrawal. PROBLEM STATEMENT Will the increase number of stimulation decrease the time taken for the snail’s eye stalk to reappear from its head? HYPOTHESIS The higher the number of stimulation, the shorter the time taken for the snail’s eye talk to reappear from its head.
VARIABLES Manipulated variable: Number of stimulation Responding variable: The time taken for the snail’s eye stalk to reappear from its head Fixed variable: Type of snail and force applied for each stimulation MATERIALS AND APPARATUS Garden snail, cotton bud, distilled water and stop watch PROCEDURE 1. A garden snail of significantly size is used and placed on a clean, firm surface. The snail is allowed to acclimatize to its new surroundings for a few minutes and its acclimatization is indicated when its head has fully-emerge from its shell. 2.
A clean tone wool bud is dampened with water. 3. Between the eye stalks the snail is firmly touched with the dampened cotton wool bud and the stopwatch is immediately started. The length of time between the touch and the snail being fully emerged from its shell once again, with its eye stalks fully extended is measured. 4. As soon as the eye stalks fully reappeared, steps 3 to 5 is repeated for a total of 10 touches, and how long the snail takes to re-emerge each time is timed. 5. The results is recorded in a suitable table and presented in an appropriate graph.
RESULTS The number of stimulations The time taken for eye stalks to emerge from the head of the snail/ seconds, s 1 26 2 25 3 4 19 5 20 6 17 7 15 8 9 12 10 11 Table 1: Time taken for eye stalks to emerge from the head of the snail for 10 touches of stimulus Graph 1 : Graph of time taken for snail to fully re-emerge from its shell against number of stimulation DISCUSSION From the graph, we can see that the snail showed the habituation response towards stimulus. During the first touch, the time taken for the snail’s both eyes to fully re- emerge was 26 s.
The duration of time taken continue to decrease as the number of ouches received by the snail increases. During the last touch (10th touch), the time taken fell to merely 12 s. However, there was one slight anomaly from the data, which is from the 5th stimulation, the time taken increases when it should have been decreasing. However, in general, we can conclude that the time taken for the snails to retreat and re-emerge decreases as the no. Of stimulus increases. There is a considerably clear negative correlation between the number of stimulations and the time taken for eye stalk withdrawal.
This is because if a regression line is drawn, the radiant would be a negative value, meaning both the variables are negatively- correlated. The decrease in time taken for eye-stalk withdrawal is due to habituation. It is believed that the calcium ion channels on the pre-synaptic neuron membrane of the snails are less responsive to the calcium ions after more and more stimulations. Hence, less calcium ions will diffuse into the pre-synaptic neuron. This causes less synaptic vesicles (which carry neurotransmitters) move and bind to the pre-synaptic neuron membrane to release the neurotransmitters via cytosine to he synaptic cleft.
As a result, the post-excitatory generator potential at the post- synaptic neuron membrane is not high enough to reach the threshold level to generate an action potential. This is the reason for the snail becomes habituated and takes less time to get dully emerged trot its shell again tater continuous stimulations. This mechanism is useful to snails particularly in the wild as sometimes when snails faced danger or are in a dangerous situation, the withdrawal of it head into its shell will enable it to protect itself from the danger.
However, after several mimes of stimulation, the time taken for the snail’s head to re-emerge will be shorter and after some time, the snail would not even response to the stimulus. This is when habituation happens. Habituation allows animals to ignore unimportant stimuli so that the limited sensory attention and memory resources can be concentrated on more threatening or rewarding stimuli. The snails cannot be handled regularly before the experiment. Actions such as shaking the surface or using objects to touch parts of the snail will lead to the snail becoming slightly habituated to the touch tumulus.
Therefore, once the snail is touched for the first time during the experiment, they may have already become habituated to this type of stimulus so further stimulations will not change the response. Hence, results will be largely inaccurate. Superman’s rank, RSI correlation coefficient Number of times the snail has been stimulated Rank stimulation Time / seconds Rank time Difference/D -9 81 49 -5 Table 2 shows Superman’s rank, RSI correlation coefficient data. Superman’s rank, RSI correlation coefficient, Where = rank stimulation – rank time = 10 Based on table of critical value and by using significance value of 5% = 0. 5 the critical value was found out to be -0. 564 Using the table, with n=10, and the level of significance, 0=0. 05, therefore the critical value would be 0. 564. As 0. 564 is smaller than the Superman rank value (0. 988), therefore, the null hypothesis can be rejected. Hence, alternative hypothesis is true, that is there is a significant negative correlation between the number of stimulation and the time taken for the eye stalks of the snail to reappear from its head with a 5% significance. Limitation There are some limitation occurred when the experiment is carried out.
One of the limitations is the difference in the amount of force applied to stimulate the snail. This is a minor human error which can hardly be controlled. A stronger or weaker force will generate different generator potential and thus affecting the reaction time of the snail to re-emerge. Besides, the original habitat of garden snail is different with the site of the experiment. The snails might be unable to adapt with the climate in a short period of time, thus affecting the activity of the organism. Therefore, each snail just be left to adapt with the surrounding over a period of time before they are being used in the experiment.
Moreover, due to the rounded-tip of the cotton bud used, the touch on the snail cannot be done on the same spot. Sometimes the touch fell in between the eyes and sometimes on the eye itself. Hence, the time taken of the habituation response was not so accurate. Sources of error In this experiment, there are a few sources of error which could affect the validity of the experiment. Firstly, the different standards are set upon to decide whether the eye stalks has fully extended or not. Thus we might have stopped the stopwatch earlier or later than it supposed to be, causing the result is not accurate.
However, we can reduce this error by having the same person measuring the time taken throughout the experiment. Besides, we can wait for 3 seconds after the snail was thought to be fully withdrawn for every reading. This helps to standardize and clear the ambiguity whether the eye stalks has fully extended or not. Another source of error is when the snails reach the edge to the tall surface and I t NAS to be moved back to the centre of the surface by students to continue the experiment. This is also considered as stimulation although its eye stalks are not directly touched.
