11.2 Frequency discrimination Some findings indicate that, for moderate loudness levels, humans can detect a frequency change of about 1 to 3 Hz for frequencies up to about 1000 Hz. Figure 37 shows a plot of the smallest frequency difference for which two tones can be discriminated for a number of reference tones. You can see from the figure that up to about 1000 Hz, the D
2.4.1 Electromagnetism and fields When Newton wrote about ‘The System of the World’ in Part 3 of Principia, the only forces he could discuss in any detail were the contact forces that arose when one object touched another, and gravity, which acted at a distance. Even so, Newton thought that there were other forces at work in the world, and hoped they might eventually be brought within his overall scheme just as gravity had been. In fact, Newton wrote: 6 Phylogeny and cladistic analysis In Section 3.3 the point was made that many physiologists consider that desert birds are successful because of their avian physiology, not because of any specific adaptations. While Williams and Tieleman's research on hoopoe larks demonstrated that desert species are capable of flexibility in metabolic rate and evaporative water loss, it suggested that adaptation is important too. The selective advantages of lowered BMR and TEWL for desert birds include reduced energy demand, and lower produc 10.3 Fluid balance Although a person can survive for several weeks without food, without fluids, someone can survive for only a few days. A loss of water equivalent to just 1% of body weight is enough to make someone feel thirsty and to have an effect on ability to concentrate. Such a loss has been shown in some studies in schools to result in a 10% decrease in the mental performance of children. A 4% loss results in dizziness and reduced muscle power. By the time there is a 6% loss, the heart is racing and swe 3.7 Vitamin C (ascorbic acid) What is the condition that results from vitamin C deficiency and what are its symptoms? You will probably remember from the start of this 3.6.6
Vitamin B12 (cobalamin) Vitamin B12 is yet another group of compounds, this time with an atom of the metal called cobalt (present in only trace quantities in the body) in their structure, hence the alternative name ‘cobalamin’. Vitamin B12 works alongside folate and if levels of it are low, folate deficiency symptoms occur too. It is stored in the liver and in general the body does not appear to need a regular intake. Many people have enough B12 stored in their liver to last for 3.6 Vitamin B Vitamin B, often called the vitamin B complex, consists of a whole range of different compounds, some of which have similar functions and work together. However, unlike the families of compounds forming vitamins E and K, the B vitamins are sufficiently different from one another to be given individual names or numbers, and to be listed separately on many food labels. Except for vitamin B12, the body can only store limited amounts of B vitamins and because they are all water-soluble 1.3 The aspirin story As long ago as 400 BC the physician Hippocrates, from the island of Kos (now a popular Greek holiday destination) prescribed a concoction made from willow leaves to help relieve the pain of childbirth. Ever since then (and probably even before) herbal remedies based on the leaves or bark of willow trees have been used for the alleviation of pain and fever. In the 1840s the chemists of the day were able to extract the substance salicin from the bark of willow trees by treating it with boiling 1.2.3 The transmission of genetic material The full complement of 46 chromosomes in the human genome, the diploid number, is restored at fertilization. As Figure 3.1 shows, all the somatic cells and cells in the testes and ovaries arise from the same fertilized egg by the process of mitosis; the cells all contain copies of the same genetic material (with some exceptions). 1.3 Chromosome structure and DNA replication DNA replication is closely linked to chromosome replication, which in turn is linked to cell division, which includes the nuclear division of mitosis. This raises an intriguing question: how many DNA molecules are present in a chromosome? Chromosomes are composed of DNA intimately associated with proteins. When the chromosomes become visible at the beginning of mitosis, the DNA has already been replicated, and the chromosomes are double structures; that is, each chromosome consists of t 3.2 Magnetic field in a perfect conductor When discussing the Meissner effect in Subsection 2.3, we argued qualitatively that a material that just had the property of zero resistance – a perfect conductor rather than a superconductor – would maintain a constant magnetic field in its interior, and would not expel any field that was present when the material became superconducting. We shall now show how that conclusion follows from an application of Maxwell's equations to a perfect conductor. We can then see what additional assumpt 1.5 Key dissertation ingredients A number of ingredients are essential for a satisfactory dissertation: a thesis, i.e. one coherent overriding ‘story’ or argument situation in existing knowledge, i.e. a critical review of prior research which motivates and justifies the research question contribution of something new appropriate voice and argument, i.e. the provision of clear and explicit evidence, substantiation, and chain of in 4.3 Seismic energy It is also possible to relate magnitude to the seismic energy released by an earthquake. An increase of one unit on the Richter scale represents an increase of about 40 times in the amount of seismic energy released. What i 4.2 Earthquake magnitude The magnitude of an earthquake is a measure of the amount of seismic energy released by it, so it is a quantitative scale. The scale of earthquake magnitude is called the Richter scale. Its development is described in Box 4, Charles Richter and the Richter earthquake magnitude scale. The Richter magnitude 3 Where do earthquakes occur? How deep in the Earth do earthquakes occur? Most earthquake foci are within a few tens of kilometres of the surface. Earthquakes less than 70 km deep are classified as shallow-focus. Earthquakes with foci 70–300 km deep are classified as intermediate-focus and those below 300 km are deep-focus (Figure 7). Shallow-focus 3.3 The struggle for existence During their lives, guppies face a variety of environmental hazards which cause mortality. They must find food and, if food supply is limited, some will die through starvation. Heavy rain periodically causes floods which may wash a large part of a population out to sea; occasional droughts cause populations to perish when streams dry out. Like all organisms, guppies are attacked by a rich variety of parasites and diseases. Of most interest to us in this discussion is that guppies are preyed u 1.3.9 Internet resources There are many websites where you will find useful information on science and nature. With all information on the internet you need to make a judgement on the reliability of the information
Activity 14
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