7.7 Physical hazards

In any laboratory, potential hazards arise from the use of electrical equipment. The legal requirements relating to the use and maintenance of such equipment are contained in the ‘Electricity at Work Regulations 1989’ (EAW). The regulations require certain safety objectives to be achieved but do not prescribe in detail the measures to be taken. Instead, precautions should be selected appropriate to risk depending on particular work activities.

‘Portable’ electrical equipment –
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5.2 Cryogenic liquids and ionising radiation safety

5.2.1 Cryogenic liquids

There are a number of hazards associated with cryogenic liquids, the main one being that when accidentally released the liquid expands hugely to form a gas (600 times in the case of nitrogen). The formation of such a large volume of gas can lead to asphyxiation in confined areas.

The other main hazard is cold burns (frostbite).

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4.1 Vitamin A deficiency

Vitamin A, more properly known as retinol, is an important chemical intermediate in a number of biochemical processes in mammals. It is involved in vision, and is found in the rod cells of the retina of the eye. These cells are particularly important in seeing at low light levels, and night blindness is a symptom of vitamin A deficiency (VAD). Vitamin A is also involved in the proper functioning of the immune system. Children suffering from VAD are prone to serious infections, and often die f
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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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1 How do organisms acquire iron?

Metals are an essential part of biological chemistry. Of all the trace elements, iron is the most important, especially as it is present in many essential enzymes and proteins. But how do organisms acquire the iron from their surroundings? Clearly, organisms need to absorb iron biochemically before it can be used in proteins. Also, some method of replacing lost iron quickly is needed: for instance, how is blood replaced once it has been lost through a cut? This prompts the question: what bioc
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Introduction

In this unit we will see 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. For example, iron storage in mammals, including humans, is achieved by ferritin, which stores iron as a hydrated iron(III) oxide – an example of biomineralisation.

This unit is from our archive and is an adapted extract from
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1.3 Protein secondary structure

From our consideration of the steric constraints that apply to peptide bonds and amino acid residues in a polypeptide, we have already begun to discuss some of the factors that determine how the backbone of the polypeptide folds. The conformation adopted by the polypeptide backbone of a protein is referred to as secondary structure. Whilst it is true to say that all proteins have a unique three-dimensional structure or conformation, specified by the nature and sequence of their amino a
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1.1 So what's it all about?

iSpot is a website aimed at helping anyone identify anything in nature. Once you've registered, you can add an observation to the website and suggest an identification yourself or see if anyone else can identify it for you. You can also help others by adding an identification to an existing observation, which you may like to do as your knowledge grows. Your reputation on the site will grow as people agree with you identifications. You may also like to visit our forums which offer lively debat
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1.6.4 Drop-towers revisited

In Section 1 we described how research into near weightless conditions can be carried out on Earth by using a drop-tower or a drop-shaft (Figure 41). We are now in a position to examine drop-shafts in more detail (Example 3).

Figure 41
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1.5.5 Derived functions and derivative notation

Given the function x(t) that describes some particular motion, you could plot the corresponding position–time graph, measure its gradient at a variety of times to find the instantaneous velocity at those times and then plot the velocity–time graph. If you had some time left, you might go on to measure the gradient of the velocity–time graph at various times, and then plot the acceleration–time graph for the motion. This would effectively complete the description of the m
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1.5.4 Functions and the function notation

In Figure 25, the position x of the car depends on the time t. The graph associates a particular value of x with each value of t over the plotted range. In other circumstances we might know an equation that associates a value of x with each value of t, as in the case of the equation x = At + B that we discussed in Section 3. You can invent countless other ways in which x depends on t: for instance x = 
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1.5.3 A note on functions and derivatives

This subsection introduces two crucially important mathematical ideas, functions and derivatives, both of which are used throughout physics.


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Learning outcomes

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

  • identify the charactistics of primates and explain the main differences between the two suborders, prosimians and anthropoids;

  • describe the detection of colour and estimation of distance in primates and explain the advantages of stereoscopic trichromatic vision;

  • discuss the various types of communication seen in anthropoids and explain how playback experiments contribute to understanding vocal communica
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8.3 Shortage of minerals

You may be familiar with salt licks that are provided for domesticated cattle. In the wild, grass is also often low in minerals (e.g. it has almost no sodium and very little calcium), so grazers may have to go to extraordinary lengths to supplement their diet with additional minerals obtained from the most unlikely places. LoM gives some examples, but the most impressive activity takes place in the caves of Mount Elgon in Kenya [pp. 113–114]. You'll probably recall this spectacular footage
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5.3 Hindgut fermenters

The odd-toed ungulates (comprising the order Perissodactyla), the horses, tapirs and rhinoceroses, are hindgut fermenters, as are elephants. Update Table 2 with this information. These animals have a relatively simple, small undivided stomach, but this time an even larger caecum and colon where the microbes are housed and whe
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6.1 Basic isotropy

As we have said, the photons in the 3 K background have been practically free from interaction with anything since about 4 × 105 years after the instant of the big bang. The present angular distribution of the microwave radiation – the way in which it is spread across the sky – is therefore almost the same as it was then. The spectrum we find today depends on the temperatures at that time – for the intensity of the radiation in a particular region of the early Unive
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5.3 The redshift of the 3 K radiation

The temperature, T, of the radiation is proportional to the most probable photon energy, E, which as we have said is proportional to f, and hence inversely proportional to the wavelength λ. Thus,

According to Equation 1, we have for the redshift, z


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5.2 The origin of the 3 K radiation

In speaking of the radiation as having a cosmic origin, what do we have in mind? Essentially this:

In the violent conditions of the early evolution of the Universe, a stage was reached where the matter consisted of a plasma of electrons, protons, neutrons, and some light nuclei such as helium. There were no atoms as such for the simple reason that atoms would have been too fragile to withstand the violence of the collisions that were taking place at the temperature that then existed. As
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5.1 A second major discovery

In the introduction to this unit, we said that there were three pillars of evidence for the big bang. We now turn to the second. It rests on a discovery that ranks in importance with that of Hubble's law. It came about when observations in a new region of the electromagnetic spectrum – the microwave region – became possible. This was due to the invention of new detectors, working at frequencies as high as 30 000 MHz. In 1965, two Bell Telephone scientists, A. Penzias and R. Wilson, were i
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4.2 Evidence for a big bang

Having interpreted the redshift as indicating a recessional speed proportional to distance, one may extrapolate into the future to predict how the positions of the galaxies will evolve with time. One can also run the sequence backwards, so to speak, to discuss what their positions were in the past. Clearly, at former times the galaxies were closer to each other.

But not only that. Because of the proportional relationship between speed and distance (Equation 6), at a certain time in the
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