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2.7 Inferring relationships of common ancestry

Activity 6

0 hours 10 minutes

This clip addresses the question of how one might go about building a tree, or inferring relationships of common ancestry, by recognising evolutionary novelties, or share
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4.1 Introduction

Simple theories of chemical bonding are based on the idea of the electron-pair bond, and the extent to which the electron pair is shared between the bound atoms. There is also an assumption that the electronic structures of noble gas atoms are especially stable, and that many elements try to attain these structures when they react to form chemical compounds. These ideas were the brainchild of the American chemist, G. N. Lewis (Box 3). In developing them, we shall simplify the electronic confi
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1.2 Chemical elements

Atoms of the same atomic number behave virtually identically in chemical reactions. They are therefore given the same chemical name and chemical symbol. For example, the atom of atomic number 6, which is shown in Figure 1, is a carbon atom, whose symbol is C. All materials are made of atoms, but there is a special class of substan
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2.2 Wave packets and scattering in one dimension

Figure 6 shows the scattering of a wave packet, incident from the left, on a target represented by a potential energy function of the form

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2.1 Overview

Session 2 discusses the scattering of a particle using wave packets. We shall restrict attention to one dimension and suppose that the incident particle is initially free, described by a wave packet of the form

This is a superposition of de Broglie waves, with the function
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Introduction

In this unit we shall consider two physical phenomena of fundamental importance: scattering and tunnelling. Each will be treated using both a stationary-state approach and a wave-packet approach.

We can consider two approaches to describing the state of a system in wave mechanics. In cases where the probability distributions are independent of time, a stationary-state approach can be used. In other cases, where probabilities are time-dependent and motion is r
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Acknowledgements

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The author of this unit is Peter Sheldon.

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5 The Devonian Period

Before going any further, click on 'View document' below and read pages 76–77 from Douglas Palmer's Atlas of the Prehistoric World. Do not worry too much about all the different names of fish groups in this, the ‘Age of Fishes’.

4.4 Other Wenlock Limestone fossils

Among the other fossils common in the Wenlock Limestone are brachiopods (Figure 12a and b), gastropods (Figure 12c) and bryozoans (Figure 12d). You may need to reread Section 1.3 to remind yourself about various aspects of these groups.

Figure 13 (the unit image) is a reconstruction of a typical scene from a Wenlock Limestone environment. See
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4.1.1 More on trilobites

Many thousands of trilobite species are known, mostly from Cambrian to Silurian rocks, and all were confined to the Palaeozoic Era. By the time trilobites became extinct in the late Permian, their diversity had dwindled to a small number of species, and the group was long past its peak. The variation in trilobite form is enormous, but the basic three-lobed division of the exoskeleton is always present. The number of trunk segments varies from 2 to 40. Not all have eyes. Most are about 2–10
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4.1 Trilobites

As we've seen, the Cambrian explosion left the seas teeming with a huge variety of animals. In the following activity you will study some of the marine life at one particular time in the Palaeozoic Era – the middle part of the Silurian Period, 430 Ma ago. You'll look in detail at some fossils which come from a deposit in the UK called the Wenlock Limestone, famous for its many beautiful fossils. The Wenlock Limestone crops out mainly around Birmingham and the borders of Wales.

Figure
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12 Glossary

You can access the unit glossary by clicking the link below.

Open glossary now...


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6.1 Introduction

Despite efforts to avoid them, heart disease, heart failure and heart attacks do occur – sometimes with warning symptoms and sometimes without. Cardiologists (doctors specialising in the heart) use a variety of tests to determine the causes of different conditions leading to heart disease. They are then able to guide subsequent treatment. Special tests that are carried out in cardiology departments may include blood pressure measurements, blood tests, electrocardiography, angiography, echoc
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4.6 A balanced diet

Our diet is simply what we eat and drink. Diet does not mean that we are trying to lose weight, although sometimes this is necessary. What we eat is very important, particularly in people with diabetes (as you found out in Section 3). Our wellbeing is influenced by whether or not we eat a balanced diet. A balanced diet is one
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3.2.1 Fats

Fats, also known as lipids, are important components of living tissues, and are used by the body for making cell membranes and for storing energy. Fats come in a variety of different biochemical types, which may be obtained from the diet or can be synthesised within the body. Many cells of the body can convert certain types of fat into others, but by preference, fats will be obtained from the diet, if available. The fatty acids that cannot be synthesised by the body and therefore must
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Acknowledgements

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2.14 Samples and populations

It is no accident that the examples used to illustrate the statistics for repeated measurements of individual quantities were drawn from chemistry and physics. Experiments involving repeated measurements of some quantity are typical of the physical sciences. There are, however, many other types of scientific work in which a typical procedure is to collect data by measuring or counting the members of a sub-set of things which form part of a larger group, and
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2.10.1 Mean and standard deviation for repeated measurements

In everyday terms, everybody is familiar with the word ‘average’, but in science and statistics there are actually several different kinds of average used for different purposes. In the kind of situation exemplified by Table 2, the sort to use is the mean (or more strictly the ‘arithmetic mean’) For a set of measurements, this is de
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