4.1 Exhaust pollutants The most important chemical reaction in a petrol engine – that is, the one that provides the energy to drive the vehicle – is the combustion of fuel in air. In an ‘ideal’ system, combustion would be complete so that the only exhaust products would be carbon dioxide and steam. In practice, the complete oxidation of the fuel depends on a number of factors: first, there must be sufficient oxygen present; second, there must be adequate mixing of the petrol and air; and finally, there must
Introduction Ensuring good quality air is essential for the protection of public health. Governments worldwide have adopted a range of increasingly demanding measures to curb air pollution with a particular focus on the emissions from motor vehicles. An important part of this strategy has been the development of the three-way catalytic converter to remove exhaust pollutants such as carbon monoxide, unburnt hydrocarbons and nitrogen oxides. This unit takes an in-depth look at the construction of this conve
9.1 The psychological arena The examples in the previous section followed the traditional medical approach, namely that there is a disease, it can be diagnosed (identified), and the cause of the disease, be it viruses, bacteria, pathogens, genes or poisons, can be sought. This section moves away from the medical arena and into the psychological arena, where the symptoms are behavioural. In this case, the symptoms are socially unacceptable behaviour and to the list of causes just mentioned is added family circumstances a
7.8 Summary of Section 7 This section has sought to illustrate the formation of connections between neurons and their targets by exploring a few examples. The picture that emerges is one of cells at different stages of development subjected to a vast array of signals. These signals are the medium through which environmental factors exert their effects. To some of these signals, some cells respond; to other signals, other cells respond. What a cell, a neuroblast, a growth cone actually does is dependent on the combina
6.5 Summary of Section 6 Growth cones respond to proximal and distal cues. The proximal cues in the extracellular matrix or other cells affect adhesion and result in chemotactic guidance. Distal cues are also in the extracellular matrix but they diffuse through it and result in the growth cone either moving towards the source (attractants) or away from it (repellants). These distal cues are chemotropic cues and can have different effects on different growth cones; what may be an attractant to one growth cone may be r
4.4 Summary of Section 4 Two important points emerge from this section. The first is the powerful effect of maternal contact on the development and later behaviour of their charges. In the Feldman study the disadvantages of prematurity were essentially overcome by early maternal contact. The second point is that some behavioural traits really do run in families, without being genetic. The Francis study clearly showed that some aspects of Open Field behaviour were the result of nursing care.
Learning outcomes After studying this unit you should be able to: recognise definitions and applications of each of the terms printed in bold in the text; critically evaluate statements about the influence of the genome on behaviour; explain the ways in which genetic and environmental factors influence the development of the nervous system; provide examples of the influence of genetic and environmental factors on the development of the nervous s
4.4.1 Phosphorus (P) Like calcium, phosphorus is important in the structure of bones and teeth. It is vital in the body as part of the molecules ATP and DNA, and is also a component of phospholipids, lipoproteins and many other proteins too. Phosphorus can occur, combined with oxygen, in phosphate ions and in this form it plays an important role in switching on and off metabolic pathways in cells. Phosphorus is widely available in the diet, from both plant and animal sources, such as meat, fish, eggs and dairy pr
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 3.6.5
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 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 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, Learning outcomes After studying this Unit you should know: that certain minerals are required in the body and that some minerals form essential structural components of tissues; that sodium, potassium, calcium and chloride ions are important in maintaining the correct composition of cells and of the tissue fluids around them (homeostasis); that some minerals are essential components of important molecules such as hormones and enzymes; that the correct 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 2.0 Licence All other materials included in this unit are derived from content originated at the Open University. 1. Join the 200,000 studen 9 Summary In this unit you have found out that: The sensation of pain is caused by the release of a chemical (prostaglandin) that stimulates the nerve endings and sends an electrical message to the brain. Pain can be reduced if the formation of prostaglandin can be inhibited. Prostaglandin is formed, from arachidonic acid, in a cavity in the active site of the enzyme cyclooxygenase (COX). Geometrical isomerism 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 1.7.2 How enzymes work Enzyme molecules have an ‘active site’ that is a specific shape for a given enzyme. It is here that reactant molecules are converted into products. The active site binds to and holds the reactant molecule in exactly the right position for the reaction to take place. Effectively it fits around the molecule rather like a glove fits around a hand. This very precise three-dimensional structure can only be achieved by enzymes being large complex molecules. Because the enzyme fits the re 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).
Activity 14
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