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Biology coursework investigation: Comparing the length of ivy leaves (Hedera helix) in areas of greater illumination and shade

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Introduction

Biology coursework investigation: "Comparing the length of ivy leaves (Hedera helix) in areas of greater illumination and shade" Abstract The aim of this study was to compare the length of leaves of ivy plants (Hedera helix) climbing on two Hornbeam trees (Carpinus betulus) in two different light intensities. The hypothesis was that the lengths of Hedera helix exposed to a higher light intensity ("sun leaves") would be shorter than Hedera helix exposed to a lower intensity of light ("shade leaves"). The light intensity was measured using a light meter and the lengths of the midrib vein of 30 leaves were measured from each of the two trees. The method describes how leaves were chosen to ensure that they were approximately the same age. The results were analysed using a students t statistical test and it was concluded that there was a significant difference between the lengths of the two groups of leaves. The main reason for this was concluded to be the structural differences in the Hedera helix in the sun and shade. Background information on Hedera helix Previous investigations have shown that there are structural differences between the leaves of ivy in areas of high light intensity and areas of low light intensity. Shade leaves of ivy are typically thinner than sun leaves and also have a larger area in comparison. This is due to them having a thinner cuticle and one layer of palisade tissue cells whereas sun leaves usually contain two or three layers of palisade cells that are often longer and also have a thicker cuticle. Low light intensity causes the shade leaves to grow rapidly producing long internodes thus helping the leaves to catch any light in the plant's surroundings. This rapid growth helps the shoot to reach light subsequently helping the plant to survive in an area where light levels are low. The large leaves of the shade plant provide a larger surface area for trapping light energy for photosynthesis for maximum absorption. ...read more.

Middle

5.9 25 5.9 146.5 5.9 26 5.7 152.2 5.9 27 7.5 159.7 5.9 28 5.3 165 5.9 29 4.0 169 5.8 30 6.5 175.5 5.9 Table 2: Measurements of Hedera helix in the shaded area Leaf number Length (cm) Cumulative total (cm) Cumulative mean (cm) (1 d.p.) 1 12.0 12 12.0 2 8.2 20.2 10.1 3 10.5 30.7 10.2 4 9.5 40.2 10.1 5 9.0 49.2 9.8 6 8.0 57.2 9.6 7 9.0 66.2 9.5 8 9.4 75.6 9.5 9 9.7 85.3 9.5 10 8.6 93.9 9.4 11 7.3 101.2 9.2 12 10.8 112 9.3 13 10.7 122.7 9.4 14 11.0 133.7 9.6 15 9.5 143.2 9.5 16 9.2 152.4 9.5 17 9.0 161.4 9.5 18 8.5 169.9 9.4 19 8.5 178.4 9.4 20 12.0 190.4 9.5 21 9.7 200.1 9.5 22 9.0 209.1 9.5 23 9.6 218.7 9.5 24 9.9 228.6 9.6 25 7.5 236.1 9.4 26 10.5 246.6 9.5 27 10.0 256.6 9.5 28 10.0 266.6 9.5 29 9.7 276.3 9.5 30 9.5 285.8 9.5 The results displayed in the tables above have also been recorded in a tally chart as shown below: Length of Hedera helix (cm) Number in brighter area Number in shaded area 1.0 - 1.9 2.0 - 2.9 3.0 - 3.9 4.0 - 4.9 111 5.0 - 5.9 111111111111111 6.0 - 6.9 11111111 7.0 - 7.9 1111 11 8.0 - 8.9 11111 9.0 - 9.9 11111111111111 10.0 - 10.9 111111 11.0 - 11.9 1 12.0 - 12.9 11 The results in the tally have been displayed in the graph below to compare the two sets of data: Results The results table and graph clearly display evidence to support my hypothesis. The tally chart shows that the lengths of the Hedera helix in the shade were greater than Hedera helix in the sun. From the graph it can be seen that there appear to be notable differences in the lengths of the two sets of leaves, in particular between the ranges of 5.0-5.9 cm and 9.0-9.9 cm, where the majority of the sun and shade leaf lengths lie respectively. ...read more.

Conclusion

It can be seen from the graph that the measurements of the two groups show considerable variation with very little overlap. There is only overlap in the size class of 7.0-7.9 cm. The shade leaves cover a wider range of measurements thus showing more variability than the sun leaves. This is also apparent in the size differences in some of the sun leaves and shade leaves with some shade leaves measuring double the length of some sun leaves, e.g. 3 sun leaves fell into the size class of 4.0-4.9 cm whereas 5 shade leaves measured between 8.0-8.9cm. Therefore the difference in size between the two groups of leaves is indeed very significant as shown by the t test. A limitation of this study is that it only measured the length of leaves and not the area which may have produced different results. However, this is not likely to be the case as length is proportional to area so it is likely that the results would be very similar to those obtained in this study. Furthermore, working out the area is time consuming as opposed to working out the length which is a faster method as only a ruler is needed. Instead, time was allocated to studying a larger sample of leaves in order to have a normal distribution of data for which the t test could then be used. For further research into this topic, the area of leaves could be compared instead of length to produce results which may confirm those obtained by the investigation into length of leaves or may generate results suggesting otherwise. Leaves could also be compared for their thickness. This may be a difficult method as there is no simple technique to measure thickness of leaves as there is with length. However, the thickness of a leaf should be proportionate to its weight and area so the leaf could be measured for its area and weight after which the thickness could be estimated. Once again, this may confirm the findings of the investigation into length of leaves or may produce results suggesting otherwise. ...read more.

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4 star(s)

****A very good A-level experiment report, in which the key elements of a scientific paper are clearly attempted. To improve:
1)Give a more detailed explanation of the biology behind plant growth towards light and, the process of photosynthesis, and the role of chloroplasts and leaf structure in shade adaptation. Details should be concise, but illustrate understanding of the background biology
2)Reference all sources used in the text
3)Address sources of error and limitations of the procedure thoroughly and suggest solutions that could improve the method. This section lacks substance currently
4)Use standard format for the bibliography and evaluate sources

Marked by teacher kerry Jackson 27/03/2012

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