Learning outcomes Having read this unit you should be able to: discuss how the gas mixture expelled from the engine, and the conversion performance of the three-way catalytic converter, depend on the air/fuel (A/F) ratio; list the chemical reactions whereby the three-way catalyst removes carbon monoxide (CO), hydrocarbons and oxides of nitrogen (NOx) from petrol vehicle exhausts; interpret the results of experimental studies (involving activity test
3.5 Summary of Section 3 The developing organism is nudged onto different developmental paths by the environment in which it finds itself. Thus the experience of being premature, or of experiencing only horizontal visual stimuli, or of experiencing testosterone affects the kind of individual the organism becomes. And the effect of the environmental factors is both profound and enduring; the individual will, quite literally, never be the same again.
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
3.6.5
Folate (folic acid, vitamin B9) Folate is a generic name for a group of related compounds. The name ‘folate’ was based on the word ‘foliage’, after it was identified in a crude extract from spinach, though it is also found in liver, other green vegetables, oranges and potatoes and it is often added to breakfast cereals (usually listed as folic acid). Folate is less sensitive to heat than many of the B vitamins, though it is destroyed if food is reheated or kept hot for long periods. Folate is involved in amino acid
3.6.3
Niacin (vitamin B3) Niacin, which comprises two compounds, nicotinic acid and nicotinamide, also occurs widely in food and is added to many breakfast cereals. It is easily absorbed into the blood from the digestive system and plays a vital role in energy production in cells. It appears to reduce the levels of low density lipoproteins or LDLs in the blood and increase high density lipoproteins or HDLs, perhaps by affecting the proteins that carry the fats. This is important because LDLs are a way of transporting
3.4 Vitamin E Vitamin E is not a single compound, but consists of a group of eight closely related chemicals, of which the most important, responsible for about 90% of its activity in the body is alpha-tocopherol. Since, like vitamins A and D, vitamin E is fat-soluble, it occurs in fat-rich foods. The main sources in the UK diet are from plant oils such as soya, corn and olive oil. Other good sources include nuts and seeds, and wheatgerm (the part of the wheat grain that will develop into the new plant) an
1.1 Introduction to vitamins and why we need them Before the 19th century, one of the hazards of long sea voyages was a condition called scurvy, whose symptoms were loss of hair and teeth, bleeding gums, very slow healing of wounds, and eventually death. Hundreds of sailors and explorers died from scurvy until a Scottish physician, James Lind, in the 1750s discovered that adding a daily portion of citrus fruit to the rations of those at sea could prevent the condition, whereas adding cider, vinegar or various other substances that he tested,
1.8 Enter aspirin! Aspirin is able to release part of its ester group (Figure 15) in a hydrolysis reaction. Look again at the structure of aspirin, 2.8, and identify this group on the molecule. It is known as an acetyl group and accounts for aspirin also being called acetylsalicylic acid. The acetyl group on aspirin is fairly easily removed and can be available for forming another ester with an —OH group on another molecule; in this case, part of the structure that makes up the inside of the cavi
1.2 How does it hurt? This is a useful question because once we know the mechanism of pain sensation we can do something about alleviating it. When tissue is injured there follows a rapid release of ‘messenger’ chemicals that stimulate the nerve endings. Electrical impulses are relayed through the nerves to the spinal column and to the brain, which registers the sensation of pain. It usually, but not always, also directs our attention to the site where the damaged tissue initiated the pain message.
Introduction In this unit you will find out that the sensation of pain is caused by the release of a chemical called prostaglandin that stimulates the nerve endings and sends an electrical message to the brain. Inhibiting the formation of prostaglandin reduces pain and we will see, by looking at the specific shape of the molecules involved, how aspirin can so inhibit the formation of prostaglandin. To make the most of the material of this unit you will need to use an organic molecular modelling kit such a
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). 1.2.1 The human genome: chromosomes and genes Almost all of the different types of cell in an individual contain the same genetic material in the chromosomes, as a consequence of mitosis. You had a glimpse of the appearance of the 46 human chromosomes in Figure 1.1, and in this unit we examine their size, shape and genetic composition. Chromosomes can be regarded as strings of genes arranged along their length, rather like beads on a thread. Each gene consists of a short section of the DNA that runs the full length of each chromoso 1.1.1 Inheritance of characters Imagine you have found some old family photograph albums which span many generations. What are the distinctive family features, or characters, that demonstrate the relatedness of individuals? In other words, what characters do they have in common? For example, they might have brown eyes, a white forelock in their hair, ears that are closely attached to the head, that is, without lobes. But you will also notice the striking differences between related individuals. For example, they may differ Learning outcomes After studying this unit you should understand: that genes are the units of inheritance for individual characteristics and also may contribute to susceptibility to certain diseases; the number of chromosomes that make up the human genome and where they are located within the cell; something of the immense scale of the human genome project; how gametes are produced by the process of meiosis and how the full complement of 46 chromosomes Introduction The material presented in this unit is taken from SD805 ‘Issues in Brain and Behaviour’ – a 60-point postgraduate course within the Frontiers in Medical Science strand of The Open University's M.Sc in Science Programme. SD805 consists of two topics that are of immense worldwide social, economic, ethical, and political importance – ‘Addiction’ and ‘Author(s): 2.4 Other spectrographs Although the simple, single-slit spectrograph described above is the type you are most likely to find on a small telescope, there are other more complex designs available. Each of these has its own role to play in astronomical observations. An echelle spectrograph has a second dispersing element, either a second grating or a prism, which disperses the light at right angles to the direction of dispersion produced by the main grating. Without going into details, the effect is to pr 2.1.2 Diffraction and interference of light When light, or indeed any type of wave, passes through a narrow aperture, it will spread out on the other side. This is the phenomenon of diffraction. For example Figure 17 shows the diffraction of water waves in a device called a ripple tank. The extent to which waves are diffracted depends on the size of the aperture rel 1.2.1 The molecular level It is common knowledge that the freezing point of pure water is 0°C. Often, however, the temperature of water can fall below 0°C without it freezing, for two reasons: Any solvent containing a dissolved substance has a lower freezing point than when pure, which is why the sea freezes at a lower temperature than clean freshwater. The occurrence of supercooling, the phenomenon by which a fluid remains liquid at a temperature below Introduction In this unit, we study one aspect of the fluctuating nature of an organism's environment. We consider how organisms living in a temperate climate, such as that in Britain, are adapted to cope with winter. You will see that there is much diversity of adaptations among organisms, with different species coping with the demands of a fluctuating environment in quite different ways. As cyclic variations are a widespread feature of environments, the range of adaptations to them is an important sourc 3.2 Number of progeny Female guppies begin to breed as soon as they become mature at about three months old; they then produce clutches of eggs, most of which become fertilized, at roughly one-month intervals until they die or become too old. Clutches vary in size from one to 40 eggs; the average clutch contains about 10 eggs. Thus, female guppies produce a large number of offspring during their lives, far more than can survive to maturity.
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