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3.4 Radio galaxies

Radio galaxies were discovered accidentally by wartime radar engineers in the 1940s, although it took another decade for them to be properly studied by the new science of radio astronomy. Radio galaxies dominate the sky at radio wavelengths. They show enormous regions of radio emission outside the visible extent of the host galaxy – usually these radio lobes occur in pairs.

The first radio galaxy to be discovered, and still the brightest, is called Cygnus A (Author(s): The Open University

Active galaxies

Figure 10 shows the spectral energy distribution of an active galaxy.

Figure 10
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6.1 Introduction

Reading 5 ends with a call for a move towards a more ‘deliberative democracy’ in which public engagement takes place in parallel with the development of new technologies, so that opportunities are provided for ongoing dialogue and influence between the two. To help to achieve this, the authors argue, ‘… now is the right time to start experi
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Introduction

There are a wide range of different interactions between ‘science and the public’. Examples range from visiting a museum, or indulging in a science-related hobby, to reading a newspaper article about a breakthrough in the technique of therapeutic cloning, to attending a protest meeting about plans to build a waste disposal unit near to a residential area. Some such interactions are largely one-way; being a member of the audience for a ‘go-hear’ lecture, visiting a museum or‘‘liste
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4.4 The ongoing story

At the time of writing (2006), the Golden Rice tale is an unfinished story. Some of the developments of the last five years are summarised here.

One area of ongoing scientific dispute is the question of whether the enriched rice can contribute significantly to the alleviation of vitamin A deficiency. We have seen that Shiva estimated that at best 100 g of rice a day would provide 4.4% of the recommended daily allowance. More sophisticated theoretical models, published since that time, h
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4.3 Golden Rice in the public domain

In January 2000, the successful experiments were announced in a paper published in the American journal Science. This, in itself, is significant. Generally, work on genetic manipulation would be published in one of a number of more specialist journals. Publication in a journal like Science indicates that this was important work, likely to be of interest to a wider audience. In its ‘Notes for Authors’, the journal states that ‘Priority is given to papers that reveal novel c
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A strategy for ridding the world of VAD?

In July 2000, Time magazine announced that a potential solution to VAD had been found – ‘Golden Rice’ (Figure 8). This was a variety of rice that had been genetically modified to introduce β-carotene into the endosperm (part of the grain of the rice). The name arises from the fact that the otherwise white grains of rice are given a golden colour by the presence of carotenoid compounds.

The announcement came at the height of the global controversy over genetically modified
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2.2 Using A. tumefaciens to genetically modify plant cells

Genetic engineers have capitalised on the fact that part of the DNA from the Ti plasmid of A. tumefaciens is integrated into the plant genome during the infection process. Ti plasmids can be isolated and a foreign gene spliced in at an appropriate point, making it possible to transfer the novel gene into the plant.

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Preamble

Your answers to Activity 1 will have revealed that the initial development of commercial GM crops has focused on the introduction of two traits: herbicide tolerance and insect resistance. However, many other traits have been introduced into crops that have yet to be grown commercially on any scale. These traits include characteristics such as resistance to viral, bacterial and fungal infections, stress tolerance (for example to high levels of salt in the soil), changes to flower pigmentation,
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1 Genetic manipulation of plants and GM crops: an introduction

In this unit we will consider the genetic manipulation of plants, and the production of GM crops. A great deal has been written about the science of GM crops and the controversial issues surrounding their introduction around the world. In the study time available, we will focus on a small number of selected issues.

In this unit you'll have the opportunity to learn more about the science that has been used to engineer a range of GM crops, and examine both the science and social concerns
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Learning outcomes

By the end of this unit you should be able to:

  • understand more about the science that underlies the development of genetically modified organisms and in particular how gene transfer is brought about;

  • know something of the potential benefits and uncertainties associated with gene transfer and the high levels of technical ingenuity involved;

  • be better able to understand the science that underpins the development of Golden Rice and understand why the u
    Author(s): The Open University

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3 Summary

Hydropower was the earliest means of commercial electricity generation, and currently dominates alternative electricity supply. However, its global capacity for large-scale exploitation is less than six times that currently installed.

Growth of hydropower is slow and its contribution to global electricity supply is falling. Both are due to economic factors, the slow pace of large-scale project construction, the remoteness of high-potential sites, and increasing resistance to the social
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1 Hydropower

Hydroelectric energy is ultimately solar energy converted through evaporation of water, movement of air masses and precipitation to gravitational potential energy and then to the kinetic energy of water flowing down a slope. That energy was harnessed for centuries through the use of water wheels to drive mills, forges and textile works, before being supplanted by coal-fired steam energy. Electricity generation using water turbines, although first centred on constricted streams, has increasing
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Learning outcomes

By the end of this unit you should be able to:

  • explain the principles that underlie the ability of hydropower to deliver useable energy;

  • outline the technologies that are used to harness hydropower;

  • discuss the positive and negative aspects of hydropower in relation to natural and human aspects of the environment.


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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 unit:

Figures

Figure 3 Courtesy of Biophoto Associates;

Figu
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5 Summary of unit

We have seen in this unit that, despite having a high natural abundance, iron is in very short supply because of the insolubility of its oxides and hydroxides. A result of this is that organisms have developed methods for the uptake, transport and storage of iron. Bacteria, in particular, secrete very powerful iron chelators known as siderophores. Of all the iron–siderophore complexes, the iron(III)–enterobactin complex has the exceptionally high stability constant of 1049 mol<
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3.1 How do organisms take up iron?

Nearly all organisms are able to take up iron. However, only a handful of organisms have had their iron-uptake chemistry studied. The organism that has received most attention (other than human) is a single-cell, prokaryotic bacterium (found in the human large intestine and elsewhere), called Escherichia coli (abbreviated to E.coli), a high-resolution image of which is shown in Author(s): The Open University

2.1 The problems of iron uptake

Iron has a high natural abundance. It is the second most abundant metallic element by mass in the Earth's crust (7.1 per cent).

Activity 1

What are the main oxidation states of iron?


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Learning outcomes

By the end of this unit you should be able to:

  • describe some of the biochemical methods by which organisms uptake iron;

  • describe some of the biochemical processes by which organisms store and transfer iron;

  • explain why iron is present only in very low concentrations in aqueous solution;

  • use aspects of iron(III) chemistry to explain the role of macrocyclic ligands in iron uptake and transfer.


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3.7 Selecting the sex of a child

Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's or sister's old clothes) to the deeply religious (as described for Hindus in Section 2). In many communities there is so much social pressure on mothers to produce the ‘right’ sex (usually male) that infanticide of the ‘wrong’ sex is widely practised. Because this is illegal in most soc
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