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Investigation on the size of Limpets.

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Investigation on the size of Limpets Abstract: During my preliminary investigations, I established that sheltered and exposed rocky shores, differed immensely in their size of Limpets. Thus I was inspired to compare the size of Limpets on the sheltered rocky shore, Frenchman's Steps. The background knowledge and preliminary work enabled me conclude the following hypothesis; there will be a statistically significant difference between the size of limpets found on the sheltered rocky shore at two different vertical heights. I decided to look at 3M and 6M above chart datum for my investigation, as looking at the profile graph (appendix) the number of limpets was high at that chart datum. Aim: To determine if there is a difference in the size of limpets at two heights in there Vertical range. Scientific Background Limpets are animals that belong to the family Patellidae, subclass Prosobranchia of the phylum Molluscs. They have a strong, conical shell composed mainly of calcium carbonate, protecting the internal tissue, underneath which is a sucker, also known as the limpet foot, which allows limpets to adhere to rock surfaces, as shown in the photographs. Limpets are usually immobile unless they are foraging and so zonation is less apparent. As can be seen from the pictures above, limpets have a hydrodynamic shape so that resistance to water flow is reduced. This ensures that it doesn't overturn as it is less of an 'obstacle'. Limpets feed mainly on microalgae, using a shovel-shaped radula. As the radula, also known as the 'docoglossan', is swept back and forth across the rocks, the rows of teeth hardened with goethite (iron oxide) rasp into the rock thereby removing the microalgae and subsequently ingesting them. Once a limpet has finished feeding, it returns to its home 'scar', a shallow depression in the rock formed by the abrasion between limpet shell and rock so that its profile matches shell shape, thereby reducing rate of water loss from internal tissue during emersion. The mechanism by which this occurs is still unknown. ...read more.


0.17 28 54 0.52 12 6 24 0.25 36 59 0.61 13 12 23 0.52 24 43 0.56 14 7 30 0.23 16 37 0.43 15 3 26 0.12 26 37 0.70 16 4 18 0.22 19 30 0.63 17 16 43 0.37 23 34 0.68 18 11 24 0.46 20 32 0.63 19 8 28 0.29 18 41 0.44 20 5 21 0.24 23 40 0.56 21 17 45 0.38 33 47 0.70 22 15 35 0.43 32 62 0.52 23 10 28 0.36 24 38 0.63 24 2 17 0.12 18 35 0.51 25 1 14 0.07 23 33 0.70 26 4 27 0.15 37 58 0.64 27 6 21 0.29 25 36 0.69 28 10 12 0.83 37 62 0.60 29 13 20 0.65 33 58 0.57 30 7 28 0.25 27 39 0.69 Total 9.82 18.29 In order to show that there is a statistically significant difference between the shapes of limpets, as calculated, on lower and upper shores it is necessary to perform further mathematical analysis. When testing for any statistically significant difference between two sets of data, being the width and height ratio on lower and upper shores in this case, a T - Test is usually carried out. To calculate the t value the mean and standard deviation (a value for the spread of the data) of each set of results are worked out. Next, the value of t is calculated using the formula given. In order to interpret the resulting t value the critical value must first be determined. This takes into account the level of significance of the results used, that is the probability that the differences between the measured values and the actual values are due to chance, and the number of comparisons made between measured and actual values also known as the degrees of freedom, similar to the chi-squared test learnt at A2 level. ...read more.


This means more Limpets are able to survive on the because of the lower wave action compared to the exposed rocky shore, where wave action is high. Due to this size of Limpets is higher on the upper shore compared to the lower shore. On the upper shore the species are more mobile and therefore the Limpets are able to migrate up and down the shore according to the conditions. In my observations I noted that many Limpets had moved up to a steep rock to survive the strong wave action and high tides. But on the lower shore the Limpets are much more attached to the rocks surface and are not able to migrate in severe wave action and weather conditions and therefore may not survive but die at a young age. Overall, I think that the investigation went well, as I have managed to obtain results and graphs, which supported my hypothesis and statistical tests, which rejected my null hypothesis. All the variables that I said I would control were controlled, the same animal, Limpet was measured, the distance above chart datum was 3M and 6M, the method was the same on both vertical heights and the time was controlled as a the investigation on both heights were carried out on low tide. To extend this investigation or to provide additional evidence for the conclusion I could: * Compare the abundance of Limpets on a sheltered and exposed rocky shore, 3M and 6M above chart datum. (As I saw in my observations that number of Limpets did vary considerably on both shores) * I could compare the size of Limpets on both shores, at another chart datum, for example 5M above chart datum, to see how the results differ. * I could compare the size of Limpets 3M and 6M above chart datum, with another animal such as rough periwinkles, on the exposed and sheltered rocky shores. * I could compare the upper, middle and lower shores for their sizes of Limpets on two different shores. 1 ...read more.

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Here's what a teacher thought of this essay

5 star(s)

A thorough account of the investigation which includes good attention to detail and use of A level biological terminology throughout.

Marked by teacher Adam Roberts 20/08/2013

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