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7.6 Questions

Question 15

Suppose that a galaxy has emission lines in its optical spectrum. A line of wavelength 654.3 nm is broadened by 2.0 nm. Estimate the velocity dispersion of the gas giving rise to the broadened spectral line. Is it likely to
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7.1 The spectra of galaxies

  • The spectrum of a galaxy is the composite spectrum of the objects of which it is composed.

  • The optical spectrum of a normal galaxy contains contributions from stars and HII regions. An elliptical galaxy has no HII regions and has an optical spectrum that looks somewhat like a stellar spectrum but with rather fainter absorption lines. A spiral galaxy has both stars and star-forming regions, and its optical spectrum is the composite of its st
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6.2 Do supermassive black holes really exist?

One outstanding feature of the black-hole model is that the black hole must be supermassive. Can one at least detect the presence of a massive central object?

  • How might a massive central object be detected using information from galactic rotation curves?

  • By measuring rotation speeds near the nucleus of the galaxy. The faster the rotation speeds, the greater the enclosed mass.

So the answer is yes. In NGC 4151
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Radio-loud AGNs

The second model (Figure 36b) is similar to the first, but now the engine is producing a pair of jets that will eventually end in a pair of lobes, as seen in radio galaxies and some quasars.

Looking at the model from the side, one expects to see narrow lines in the spectrum (but not broad lines) and two
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2 What should dialogue with the public aim to achieve?

The publication Public Dialogue on Science and Technology, published in 2002 by the Parliamentary Office of Science and Technology (POST), states:

Proponents put forward two basic arguments in favour of dialogue. The first is that traditional consultation tends to be unattractive to many people and draws only on ‘predictable’ sources. They argue that dialogue can provide new opportunities for people who
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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
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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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