2.4.2 Saltmarshes Marsh plant primary production is generally nitrogen limited, so saltmarsh vegetation responds readily to the artificial eutrophication that is now so common in nearshore waters. Eutrophication causes marked changes in plant communities in saltmarshes, just as it does in freshwater aquatic and terrestrial systems. Biomass production increases markedly as levels of eutrophication increase. Increases in the nitrogen content of plants cause dramatic changes in populations of marsh plant consumer
1.2 Resource availability and species diversity A wide range of ecosystems has been studied in terms of their species diversity and the availability of resources. Each produces an individual relationship between these two variables, but a common pattern emerges from most of them, especially when plant diversity is being considered. This pattern has been named the humped-back relationship and suggests diversity is greatest at intermediate levels of productivity in many systems (Figure 1.5). 6.2 Non-covalent bonding in site-specific binding The affinity of a protein for DNA is determined in thermodynamic terms by the free energies of the individual components compared to the free energy of the DNA-protein complex. DNA binding proteins, which contain different binding motifs, demonstrate a wide range of thermodynamic strategies. The affinity of a site-specific DNA binding protein for its specific DNA sequence is generally of the order of 104−107 times greater than its affinity for non-specific sequen 5.1 Introduction The integrity of DNA as a genetic material is of paramount importance to an organism, and a multitude of proteins exist that serve to prevent or reverse damage to the DNA. However, like all biological macromolecules, DNA decomposes spontaneously. The reasons for the ease of decomposition of DNA are intimately linked to the chemical structures of the constituent bases and phosphodiester-linked sugars. The limited stability of DNA may be integral to the molecular basis of evolution. If DNA were 4.1 The varied structures of RNA RNA is a versatile cellular molecule with the ability to adopt a number of complex structural conformations. Although RNA is often thought of as a single-stranded molecule it is actually highly structured. Torsional energy can be taken up by alternative DNA conformations The energy introduced into DNA by twisting has great potential as a regulatory mechanism, since the free energy can be stored in a variety of different high-energy conformations along the chain. Base stacking Although the base pairing brought about by hydrogen bonding is responsible for the specificity of the base interactions, much of the stability of a duplex nucleic acid is due to interactions that result from base stacking. If you look back at Figure 3a, you will notice that, when seen from a side view, our schematic r Acknowledgements Except for third party materials and otherwise stated (see terms and conditions). This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence Grateful acknowledgement is made to the following sources for permission to reproduce materia 2.6 Obesity and ageing So, it seems that a part of the explanation for Ron's obesity, and the health problems that have led him to seek medical advice, may relate to the environment in which he is living, and more specifically the diet that he has chosen. It may also be a diet that is especially effective in activating the reward circuits in Ron's brain. However, Ron is also in his later middle age. A longitudinal study of people of this age in the USA suggests that average body weight increases by 1–2 kg per dec 1.5 Obesity At the time of writing (2004) 20% of the adult population of the UK is classified as obese. The number of obese children has doubled since 1982, 10% of six year olds and 17% of fifteen year olds are now classified as obese. As shown in Table 4, obesity is recognized when the BMI exceeds 30 and occurs quite simply wh 1.1 The components of a balanced diet A balanced diet contains six key nutrient groups that are required in appropriate amounts for health. These groups are outlined below. Proteins are involved in growth, repair and general maintenance of the body. Carbohydrates are usually the main energy source for the body. Lipids or fats are a rich source of energy, key components of cell membranes and signalling molecules, and as myelin they insulate neurons (nerve cells 6.2 Storing and transporting energy To be useful to us, energy must be available where and when we want it, and in a form and in amounts we can handle. Severe weather systems concentrate natural Author(s): 4 Fossil fuels Part of the incoming solar energy becomes stored in fossil fuels (oil, gas and coal: Author(s): 7.4 Models of active galaxies The standard model of an AGN consists of an accreting supermassive black hole (the engine) surrounded by a broad-line region contained within a torus of infrared emitting dust and a narrow-line region. Unified models attempt to explain the range of AGNs on the assumption that they differ only in luminosity and the angle at which they are viewed. One type of model attempts to unify radio-quiet AGNs. Type 1 Seyferts and type 7.2 Types of active galaxy All active galaxies have a compact, energetic nucleus - an AGN. Seyfert galaxies are spiral galaxies with bright, point-like nuclei which vary in brightness. They show excesses at far infrared and other wavelengths, and have strong, broad emission lines. Quasars resemble very distant Seyfert galaxies with very luminous nuclei. They are variable. About 10% are strong radio sources thought to be powered by jets of material mo Radio-quiet AGNs There has been a great deal of debate about whether there really are two different types of Seyfert or whether they can both be accounted for by the same model. For example, suppose that you look at the model AGN in Figure 36a from a direction not too far from the rotation axis of the torus. You will see 5.2 The obscuring torus If an AGN consisted solely of the central engine, observers would see X-rays and ultraviolet radiation from the hot accretion disc (accounting for the 'the big blue bump' in Figure 17) and, apart from the jets, very little else. To account for the strong infrared emission from many AGNs, the model includes a t 4.1 Introduction: the active galactic nuclei (AGN) From Section 3 you will have discovered that one thing all active galaxies have in common is a compact nucleus, the AGN, which is the source of their activity. In this section you will study the two properties of AGNs that make them so intriguing - their small size and high luminosity - and learn about the energy source Learning outcomes After studying this course, you should be able to: demonstrate a greater awareness of science-based issues of public importance demonstrate a greater insight into the phrase ‘the public understanding of science’ demonstrate a raised awareness of the ways in which the public can be consulted in relation to science policy issues think of ways in which the public might in future become more engaged in decision-making about science th 7.2 Information sources The best source of information is the material safety data sheet (MSDS). By law (CHIP3) this should accompany any chemical that is purchased. However, if this is not available, or the chemical is old, then copies can be obtained from the manufacturer's website or information can sometimes be found in the
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7.2.1 How do I find the information required to carry out COSHH risk assessments?
