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Jack H.
University of Oxford Student
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Environmental Science
TutorMe
Question:

Does the current conservation network across the European Union fulfil the political intent as well as the ecological optimum?

Jack H.
Answer:

Target 11 of the Aichi Biodiversity Targets reads as follows: “By 2020, at least 17 per cent of terrestrial and inland water areas…especially areas of particular importance for biodiversity and ecosystem services, are conserved through effectively and equitably managed, ecologically representative and well-connected systems of protected areas (PAs) and other effective area-based conservation measures”. Recognising the importance of efficiently managed and spatially arranged PAs for safeguarding biodiversity, this target provides the gold standard for conservation efforts worldwide. Consisting of 28 member states, the EU covers 4.5 million km2 of land. Simultaneously accommodating numerous biologically valuable ecoregions and more than 500 million people, intense conservation effort has been necessary to win space for natural and semi-natural ecosystems. Responsible for governing EU conservation is The Bern Convention, for which the overarching objective is “to conserve wild flora and fauna and their natural habitats, especially those species and habitats whose conservation requires the co-operation of several States, and to promote such co-operation”. EU implementation of this mandate is primarily achieved via the Birds and Habitats Directives. Established in 1979 and 1992 respectively, these two directives have provided the legal foundation for the designation of the expansive Natura 2000 (N2k) PA network. With more than 27,000 sites and a land coverage of approximately 18%, the N2k network is central to the EU’s conservation efforts, however, nationally and locally designated PAs represent a significant additional component. Despite this system being widely regarded as a conservation success story, doubts have been raised over: (i) PA spatial arrangement; (ii) network representativeness; and (iii) ability of PAs to conserve biodiversity under climate change. Fundamental to the functionality of a PA network is complementarity and connectivity. A prerequisite for high achievement in this regard is strategic spatial planning at broad scales; this is explicitly acknowledged in the N2k network objective of conservation irrespective of political boundaries. There have been many studies that have analysed connectivity of segments of the N2k network, however a relative sparsity have considered the network as a single entity. A recent study bucked this trend by comparing the observed spatial pattern with hypothetical optimal site prioritisations for three administrative levels. It was concluded that N2k design was closest to the EU optimal for Habitats Directive species and the member state optimal for Birds Directive species. This finding is likely to be a by-product of differing levels of governance employed for selection of Sites of Community Interest (Habitats Directive) and Special Protection Areas (Birds Directive). Overall, the sub-optimal allocation of sites alludes to an influence of incongruent global and local conservation priorities. As mentioned previously, the EU conservation network consists of a national PA network in addition to N2k. It would appear misrepresentative to assess connectivity and representativeness without accounting for both. Studies have shown that combining the two networks results in improved potential connectivity. Acting as stepping stones between pre-existing national PAs, the N2k network increases the quantity of connected habitat rendering the landscape more permeable for vagile species. However, the discovery that N2k covers Directive species better than non-Directive species emphasises the need to qualify the appropriateness of the currently prioritised species. As a signatory to major climate change agreements such as the Kyoto and UN Montreal Protocols, the EU is at the forefront of climate change awareness. However, the vast majority of PAs in the current conservation network were selected prior to the cementing of this standpoint, and so it is likely that the current designation is poorly suited to conserve biodiversity in the context of a changing climate. Evaluation of suitability requires a general appreciation of species’ responses to climate change, which are broadly restricted to range and phenology shifts. Species-specific range shifts can be predicted using bioclimatic envelope models, which extrapolate current habitat requirements to determine range size and location changes under projected alterations to relevant bioclimatic variables. Studies that have adopted these models have predicted the majority of terrestrial vertebrates and plants to lose suitable climate conditions in EU protected areas. This forecasted suitability reduction insinuates that future conservation effort must exceed current levels to ensure widespread species longevity. Comfortably surpassing the landscape coverage goal of 17% outlined by the Aichi Biodiversity Targets, the EU’s current network of conservation effort is generally regarded as exemplary. Representativeness is also high, however, the extent of connectivity, whilst moderate, leaves room for improvement: spatial allocation of sites is sub-optimal, reflecting a violation of the N2k intention to disregard political boundaries. This apparent fragmentation is particularly concerning in the context of accelerating climate change, as climate conditions in EU PAs are predicted to decrease in suitability. Extrinsic factors ensure that future establishment of novel PAs appears unlikely: high anthropogenic disturbance in the background matrix and the economic and political costliness of PA maintenance are two prime suspects. Therefore, maximising the efficiency of the EU’s conservation network requires a many-pronged approach: (i) quantification of system redundancy; (ii) optimisation of spatial site allocation; (iii) incentivisation of biodiversity conservation in the matrix; and (iv) determination of the relevance of the Directives species lists. The primary obstacle to attainment of these objectives is collaboration. An extensively studied topic in the fields of international relations and environmental policy, collaboration research is surprisingly adolescent in the conservation arena. Spatial conservation prioritisation in particular would benefit from explicit incorporation of context-specific benefits and limitations of collaboration. Compounding the lack of research is poor dissemination and narrow focus. Correction of these flaws will provide a foundation from which the already moderately successful EU conservation network can be improved.

Biochemistry
TutorMe
Question:

Compare and contrast fatty acid synthesis and degradation pathways in plants and animals.

Jack H.
Answer:

Fatty acids are pivotal for several biological functions, namely structural support, signalling, secondary messaging and storage. Whilst the biochemical reactions that characterise fatty acid synthesis and degradation pathways are similar in plants and animals, they are certainly not identical. The fatty acid synthesis pathway is initiated by an irreversible event known as the committed step: the carboxylation of acetyl coenzyme A (CoA) to give malonyl CoA. This precedes an iterative process that adds two carbons at a time to the fatty acid chain. The elongation cycle is the name given to this sequence, which consists of the following four steps: condensation, reduction, dehydration and another reduction. Iterations cease once a C16-acyl ACP is formed. This is then hydrolysed unless the synthesis of longer fatty acid chains is required, in which case enzymes on the cytosolic face of the endoplasmic reticulum membrane catalyse further elongation reactions. Fatty acid synthases (FAS) are the large enzyme systems that catalyse the assembly of the long carbon chain constituents of fatty acids. These multienzyme complexes exist in two distinct forms which differ in their organisation: FAS I is found in animals, FAS II in plants. The former system has seven component enzymes linked in one large polypeptide, yields no intermediates and its sole product is palmitate. Contrastingly, the latter consists of seven dissociable, soluble compounds which each catalyse a distinct pathway step and yields both intermediates and a variety of products. Evolution of this chemical diversity of lipids produced by higher plants can be accredited to the elevated catalytic plasticity expressed by FAS II. The biological significance of this ability lies in the autotrophic nature of plants as, unlike animals, they are unable to obtain a wide array of fatty acids from their diet. Major sites of fatty acid production are the cytosol and the stroma of chloroplasts for animals and plants respectively. There is a core similarity between these two locations that facilitates effective fatty acid synthesis: NADPH is highly available. This is important as a low [NADPH] to [NADP+] ratio is detrimental to the success of reductive synthesis. Before fatty acids can be degraded via the beta-oxidation pathway, they must be linked to coenzyme A. This step activates the fatty acids prior to their entry into the mitochondrial matrix – the predominant site of fatty acid degradation. The activation reaction is catalysed by acyl CoA synthetase and occurs on the outer mitochondrial membrane. Acyl CoA is the product and also the starting molecule for the subsequent beta-oxidation pathway, a four-step sequence that commences with the FAD-mediated oxidation of acyl CoA before a hydration step, an NAD+-mediated oxidation step, and finally thiolysis by CoA. One cycle shortens the carbon chain by two carbon atoms, whilst also generating FADH2, NADH and acetyl CoA. The first major discrepancy between plant and animal fatty acid degradation pathways is the fate of acetyl CoA: animals metabolise acetyl CoA via the TCA cycle, whereas plants utilise the glyoxylate cycle. These alternative methods are largely similar with many of the intermediate steps being ubiquitous and three of the five enzymes used in the TCA cycle also featuring in the glyoxylate cycle. The crucial difference lies in the products: carbon dioxide, water and ATP are generated via the TCA cycle, whilst the glyoxylate cycle produces succinate which can be converted, through a series of further steps, into sucrose. Site of fatty acid oxidation represents another prominent contrast: the mitochondrial matrix is the major site in animal cells; conversely, this process in plants occurs predominantly in the peroxisomes of the leaf tissue and the glyoxysomes of the germinating seeds. Additionally, despite the high congruence of the pathways, the role of beta-oxidation is dissimilar in plants versus in animals: instead of aiming to provide energy, the objective for plants is to supply biosynthetic precursors. At a glance, the biochemical reactions that characterise fatty acid synthesis and degradation pathways appear to be the inverse of one another, however, upon closer inspection, three major differences are illuminated: different sets of enzymes are required for catalysis; they occur in different locations; and malonyl CoA is necessary for biosynthesis yet is not used in degradation. Furthermore, when each of these pathways are compared between plants and animals, several notable differences are evident. Discrepancies between synthesis pathways are three-fold: fatty acid synthase complexes differ; sites of synthesis differ; and plants can manufacture a wider array of fatty acids. Discrepancies between degradation pathways are two-fold: sites of oxidation differ and acetyl CoA is utilised by animals to generate ATP via the TCA cycle, whilst plants convert via the glyoxylate cycle into biosynthetic precursors. Considering the ubiquitous nature of fatty acid metabolism across the spectrum of life, it is probable that the last common ancestor of plants and animals possessed the apparatus necessary for this biochemical process. Therefore, it can be declared that these prominent differences, in all likelihood, indicate a significant evolutionary divergence.

Biology
TutorMe
Question:

Mendel's laws cannot be used to explain all forms of genetic inheritance in individuals or within a natural population. Discuss.

Jack H.
Answer:

Gregor Mendel, a scientist, Augustinian friar and abbot of St. Thomas’ Abbey in former Austria-Hungary, is widely regarded as the ‘father of genetics’ for his pioneering discovery of the fundamental principles. Despite operating in the mid-19th century, long before the detailing of the structure of DNA, he was able to use a systematic approach to formulate two laws which represent the foundation of present-day understanding of the complex field of genetics: the law of segregation and the law of independent assortment. The former dictates that each cell carries 2 copies of each gene which independently segregate during gamete formation; the latter describes how, during gamete formation, different pairs of alleles segregate independently of each other. Throughout the experimental procedures that provided the supporting evidence for these statements, Mendel disproved the two major misconceptions surrounding the inheritance of characters at the time: (1) blended inheritance, which suggested that the traits of the offspring were always an intermediate value between the two extremes displayed by the parents; and (2) homunculus theory, which proposed that one parent contributed more significantly to offspring traits. Mendel’s experimental achievements can largely be apportioned to his astute selection of both organism and traits: the short generation time of Pisum sativum allowed Mendel to cultivate and test circa 5,000 plants between 1856 and 1863; analysis of monogenic, unlinked traits ensured that results were easily interpreted in the absence of complications that may have been hard to explain given the sparsity of available knowledge. In addition, Mendel’s attention to detail alluded to an acute awareness of experimental design that ensured maximal accuracy of results. Given the complexity of genetics, it is unsurprising that Mendel’s two laws over-simplify the natural world. Violations of Mendel’s assumptions, of which the key ones were diploidy, monogenic traits, complete dominance and non-linkage, result in alternative forms of genetic inheritance referred to as non-Mendelian inheritance. Diploidy describes the condition whereby the expression of each gene is contributed to by two alleles. Human blood types, determined by three alleles (A, B, O), are one example of diploidy violation. Multifactorial traits, despite greatly outnumbering their monogenic counterparts, were not known to Mendel. It is therefore remarkable that geneticists use the guidelines of Mendelian ratios to analyse the complex network of interactions that give rise to these traits. This insinuates that multifactorial traits can be regarded as extensions to the scope of Mendel’s deductions. With regards to dominance, there exist alternative forms to Mendel’s complete dominance: codominance refers to F1 hybrids in which both of the alternative phenotypes of the pure-breeding parents are evident; incomplete dominance describes the situation whereby the F1 hybrid resembles neither pure-breeding parent. Other examples of scenarios that elude Mendelian reasoning include variable penetrance, observable when the expression of a function is affected by the environment, and when one gene contributes to several visible characters. The sheer number of forms of genetic inheritance that can’t be explained by Mendel’s laws provides ammunition for those who claim that he is lavished with too much recognition. Whilst the rediscoverers of Mendel (Hugo de Vries, Carl Correns and Erich von Tschermak) undoubtedly deserve credit for formalising and furthering Mendel’s initial forays, Mendel’s central role in the progression of the field should guarantee his status as the ‘father of genetics’. Reasoning for his exceptional success can be summarised as follows: firstly, he utilised a ruthlessly systematic approach; secondly, his experimental methods were highly effective and appropriate; thirdly, he produced reliable results through the accumulation of large samples and subsequent careful numerical analysis of the outcomes; fourthly, attention to detail was of paramount importance to him; finally, and crucially, he constructed a theoretical framework that has stood the test of time. Whilst many of his predecessors had managed to accomplish one or several of these steps, he was the first to perform them all, and in doing so, displayed unparalleled foresight and scientific aptitude.

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