6.4 Chemical equations and chemical reactions The previous section shows how different elements can either exist on their own or combine with other elements to make compounds. This section builds on these ideas by looking at chemical reactions in more detail. It also shows how chemical shorthand can be extended to describing chemical reactions. First, consider some of the molecules described earlier: water, methane, carbon dioxide and ammonia. 3 What are compounds? Click on the video clip to watch Elements and Compounds, which focuses on water and its constituent elements. Cl Faraday and Maxwell 2.3.2 Equilibrium and irreversibility As the science of thermodynamics developed beyond its industrial roots, two powerful ideas came to the fore - equilibrium
and irreversibility. These ideas were already implicit in studies of heat. You have already seen that heat flow from a hot steak to a cold plate is an irreversible process. The effect of this process is to cool down the hot steak and warm up the cold plate, leading to a more uniform distribution of temperature. The heat transfer continues until a state of equ 2.3 The irreversible Universe 'Science owes more to the steam engine than the steam engine owes to Science.' L.J. Henderson (1917) From the time of Newton until the end of the nineteenth century the development of physics consisted essentially of the refinement and extension of the mechanical view of the Universe. There were many stages in this process but one of the most interesting came towards its end with the realis References 3.3 Integration of anatomical features and biochemical and physiological strategies in evaporators Birds and larger desert mammals that use evaporative cooling risk dehydration because of the difficulty of finding sufficient drinking water. For mammals, evaporative heat loss includes panting and sweating. In small mammals and birds the temperature of exhaled air is often lower than T b, resulting in condensation of water on the nasal mucosa. Small desert mammals rely on this mechanism for water conservation, while resting in their cool burrows during the heat of the 8.3 Lissencephaly Lissencephaly, literally meaning ‘smooth brain’, is characterised by the absence of sulci and gyri, and by a four-layered cortex, instead of the usual six layers, with the majority of cortical neurons in layer four (Figure 22). Babies born with lissencephaly have a very poor prognosis; the disease proving lethal b 1 Overview You can experience this free course as it was originally designed on OpenLearn, the home of free learning from The Open University - Author(s): 3 The flow of information from DNA to RNA to protein The information flow from DNA to protein is more complex than shown in Figure 1. The genetic information encoded within the DNA of a gene is carried via an intermediary molecule, RNA (ribonucleic acid). Information within a cell can therefore be seen as passing from DNA, via RNA, to a protein. This flow of information can Acknowledgements The content acknowledged below is Proprietary (see terms and conditions) and is used under licence. Grateful acknowledgement is made to the following sources for permission to reproduce material in this course: Course image: Lars Plougmann in Flickr made available under Author(s): 4.3 Type-II superconductors For decades it was assumed that all superconductors, elements and alloys, behaved in similar ways, and that any differences could be attributed to impurities or defects in the materials. However, in 1957, Abrikosov predicted the existence of a different sort of superconductor, and Figure 23 shows direct evidence for the existence of what are now known as type-II superconductors. A comparison of Figures 23 and 22 indicates that the effect of an applied field on a type-II superconductor is rath 3.4 Penetration depth The characteristic length, λ, associated with the decay of the magnetic field at the surface of a superconductor is known as the penetration depth, and it depends on the number density ns of superconducting electrons. We can estimate a value for λ by assuming that all of the free electrons are superconducting. If we set ns = 1029 m−3, a typical free electron density in a metal, then we find that 2.3.1 Perfect diamagnetism Diamagnetism is due to currents induced in atomic orbitals by an applied magnetic field. The induced currents produce a magnetisation within the diamagnetic material that opposes the applied field, and the magnetisation disappears when the applied field is removed. However, this effect is very small: the magnetisation generally reduces the applied field by less than one part in 105 within the material. In diamagnetic material, B = μμ0H 1.5.4 Image scale The nearest equivalent definition to angular magnification that is applicable to telescopes used for imaging onto a detector is the image scale (sometimes called the plate scale). Because of the importance of angular measures, the image scale quoted by astronomers indicates how a given angular measure on the sky corresponds to a given physical dimension in an image. The most common convention is to state how many arcseconds on the sky corresponds to 1 mm in the image. Fort 1.6 Conclusion This course has presented an overview of the ways in which organisms living in temperate habitats are adapted to survive the winter. The course has shown how a limited set of environmental changes associated with the onset of winter can lead to a diversity of adaptations and therefore a large diversity of species. On the basis of the examples discussed in this course, we can identify four factors that contribute to the diversity of adaptive strategies for coping with winter. 1.2.4 The evolutionary level Life histories and trade-offs In this section, the emphasis switches from proximate (molecular, cellular, physiological and behavioural) types of explanation to ultimate types of explanation. In order to proceed, we need to understand two key concepts: life history and trade-off. Both of these concepts are important tools in organising thoughts about why organisms are so diverse. An organism's life history is the set of key biological events in its life, including b Learning outcomes After studying this course, you should be able to: identify the four main strategies shown by organisms for coping with winter appreciate and give examples of the levels and types of explanation used for understanding these strategies describe ways in which the strategies can be subjected to experimental manipulation provide examples of how plants, birds and mammals can remain active through winter give examples of orga Conclusion This free course provided an introduction to studying Science. It took you through a series of exercises designed to develop your approach to study and learning at a distance, and helped to improve your confidence as an independent learner. 3.2 Using formulas Formulas are important because they describe general relationships, rather than specific numerical ones. For example, the tins of paint formula applies to every wall. To use such a formula you need to substitute specific values for the general terms, as the following examples show.
Activity 1: Elements and compounds
Michael Faraday (1791-1867)
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Example 8
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Bozinovic, F., Gallardo, P. A., Visser, G. H., Ortes, A. (2003) Seasonal acclimatization in water flux rate, urine osmolality and kidney water channels in free-living degus: molecular mechanisms, physiological processes and ecological implications. Journal of Experimental Biology, 206, 2959–2966.
Bulova, S. (2002) How temperature, humidity, and burrow selection affect evaporative water loss in desert t
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