Method:
Safety:
*Rf value: distance travelled by pigment (mm) / distance travelled by solvent front (mm)
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Littorina saxatilis is more commonly known as the rough periwinkle which is a species of small sea snail. Hypothesis I predict that as the exposure increases due to increased wave action the size of the periwinkles will decrease. The reason I predict this is because the strong force produced by powerful wave action can dislodge the periwinkle from its position on a rock. Therefore the smaller the periwinkle the less likely it will be displaced from the rock. This means that as the wave exposure decreases, therefore in more sheltered areas, the morphology of the periwinkle is likely to increase as there is less chance the waves will be powerful enough to remove the periwinkle from the rock. Null hypothesis There is no statistically significant difference and the exposure has no direct effect on the morphology of the periwinkle. Method
Control variables
There are other important variables that cannot be controlled due to the fluctuating nature of the shore in which the experiment was undertaken. Because both the exposed and the sheltered shore are open to environmental change, variables such as temperature, salinity and competition between other organisms cannot be controlled which could influence the results. Instead of controlling these variables, the best approach is to take a record of the temperature, pH and the abundance of living organisms such as limpets and other species of periwinkle to give an indication of the level of competition in that area. By taking these uncontrollable variables into account it helps improve the validity of the results as it makes us aware of the other variables that can affect the results, so we know it is not just the level of exposure affecting the morphology of the periwinkle. Risk assessment There are risks involved to do with the shore in which the experiment took place. Both the exposed and sheltered shore could be seen as potentially quite dangerous because the rocks that the periwinkle inhabits are slippery due to the seaweed and the water, meaning there is a risk of falling over. To reduce the likelihood of falling over, protective and sturdy footwear is to be worn. T = 9.88 Degrees of freedom = 18 Critical value = 2.101 The calculated value of 9.88 is greater than the critical value of 2.101 (p=5%, degrees of freedom = 18). Therefore we can reject the null hypothesis of no statistically significant difference between the two means at the 5% significance level. Conclusion When comparing the morphology of the periwinkle on the exposed and the sheltered shore there is clearly a difference which suggests the level of wave exposure has a great effect on the size of the Littorina saxatilis. The results from the t-test also back up this hypothesis. Upon evaluation of the results of the greater the wave exposure, the smaller the periwinkle. This is shown as the periwinkles from the exposed shore had significantly smaller periwinkles compared to those of the sheltered shore. The reason for this correlation is because a greater wave exposure directly affects the ability of the periwinkle to stay attached to the rock. Therefore, those periwinkles under greater stress, that are more exposed to the waves, are smaller to reduce the likelihood of them falling off and it makes it easier to remain glued to the rock. This difference in the morphology of the Littorina saxatilis on the exposed and sheltered shore has arisen due to natural selection whereby the periwinkle with the favourable characteristic for that area has selective advantage and is more likely to survive and go on to reproduce and pass down their favourable genes. In this way, for example, the smaller the periwinkle in an exposed shore, the more likely they are to survive and pass down their advantageous genotypes to produce offspring which also show the phenotype of small size.88 References
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Ciara Branagan
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October 2016
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