From the results of the statistical tests I compared the values to the critical values table of known results. From this table at 19 degrees of freedom the results must be between 1.33-3.56 or higher to reject the null hypothesis. Therefore based upon my results I can reject the null hypothesis concerning the height of the bracken, meaning there is a significant difference in bracken growth between the two areas. However I must accept the null hypothesis is concern with the light intensity, as no significant difference has been proven between the two areas.
Conclusion: As my results concerning the height of bracken support my original hypothesis and the statistical test shows that there is very little probability that my results were obtained by chance. I can conclude that there is a significant difference between bracken growth in the two areas, but this was not proven to be due to the light intensity as there wasn’t a significant correlation between the two.
I feel that if the experiment could have been done at the same time on both sites that the light intensity results would have been more significant. Further Knowledge: I believe that the higher the light intensity such as that in a larch woodland with little canopy coverage bracken will grow higher because more light allows the plant to photosynthesise more, which would make it more abundant and grow to its full potential. In areas of increasing canopy cover such as an oak woodland bracken will still grow but not to the same heights because light becomes a limiting factor, this means it cannot do as much photosynthesis and will reach a smaller peak height because its cannot produce food to feed anything larger.
Green plants photosynthesise when there is light. The light they need is absorbed by chlorophyll found in the chloroplast cells in the leaves and stems of plants. Solar energy is converted into chemical energy and is used to convert carbon dioxide and water into glucose releasing oxygen as a by-product. The rate of photosynthesis can be limited by light. Photosynthesis involves light-dependant and light-independent reactions. The light-dependent reaction has 2 products which are needed for the light independent reaction to occur.
During the light-dependent reaction ATP and reduced NADP are produced whilst the chlorophyll molecule absorbs light energy. The process occurs because electrons in chlorophyll become ‘excited’ when exposed to light and are emitted from the leave; electrons then travel between the molecules as they act as carriers, some of the released energy is also released synthesising ATP. Reduced NADP occurs through the transfer of electrons between chlorophyll molecules, then when water replaces these missing electrons hydrogen ions and oxygen gas become released from the water. Hydrogen ions are then free to bind with the NADP reducing it in the process.
In light-independent reactions ATP and reduced NADP are used with carbon dioxide to produce sugar in the stroma of a plant. An enzyme completes the process by adding carbon dioxide to a 5 carbon sugar forming Gp (glycerate-3-phosphate). The reduced NADP then reduces the Gp using ATP forming glyceraldehydes phosphate. (Called the Calvin cycle). Competition: Competition is the striving of different organisms to obtain resources from the environment, this occurs when two or more organisms in the same community compete for some resource that is in limited supply.
The competition between organisms theory could be used to explain the difference in the height of bracken between the two areas of woodland. In site 1 (the oak woodland) I noticed that there was a higher diversity of plants in comparison to site 2 (the larch woodland). A higher diversity of species leads to more competition for resources such as water, food and light. This could explain why the bracken was not able to grow to its full potential because its resources would not allow it, whereas in site 2 there was less competition allowing the bracken to become abundant. I also discovered that the soil of larch woodland has fewer nutrients than that of oak woodland, and therefore would not be able to sustain as high a diversity of species. So where some species where not adapted for the low nutrient levels the bracken has developed genetically allowing it to take advantage, and become dominating.