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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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4.2 Digesting cellulose

Figure 3 in this section contains a lot of information and many terms that are probably new to you. Set aside the detail for the moment, read
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4.1 A brief digression about digestion

There are many new scientific terms introduced in this unit. Are you making your own lists of them? If you were to encounter these terms in a fresh context (perhaps on a website, or during your own reading around these subjects), your aim should be not just to recognise the terms, but also to understand their m
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6 Reflection

If you are working through all the units in this series, you'll be aware that this unit has taken a somewhat different tack from earlier ones. I've used rodents to explore some fundamental biological principles that have a relevance far beyond this particular order. It is especially appropriate to talk about issues such as biological success in connection with rodents, given their very wide geographical distribution and the very large number of rodent species and individuals. You'll recall (f
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5.3 The effect of environment on reproductive behaviour

Activity 5

Review your reading of Section 4.2 on the family life of marmots (or re
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7 Unit summary

Section 2

The law of conservation of charge applies locally at each point and time, so any variation of the total charge within a closed surface must be due to charges that flow across the surface of the region. This principle leads to the equation of continuity:

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1.2.1 Study Note 1

Simple rules for dealing with orders of magnitude and decimal points in decimal numbers: values ten times bigger than the order of magnitude you are looking at go to the left, ten times smaller go to the right, and less than 1 to the right of the decimal point.

Note: in many European countries, a comma is used instead of a decimal point. For instance in France and Germany two and a half (in other words 2.5) can be written as 2,5. This is important to bear in mind, for example, if
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1 Overview

As you walk down the street one day, you hear a voice from somewhere behind you that seems to be discussing this unit. It says:

‘My dad's tutor's no joker, and he told me the TMA's going to hit home with a bang.’

You turn to find the face behind the voice, which is a gravelly Glaswegian baritone, but the man has gone, leaving you to ponder what he has said. Let us call his sentence exam
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12.5 Localisation of sound in the vertical plane

Much of our ability to localise sound in the vertical plane is due to the shape of the outer ear, in particular the pinna. The pinnae provide a monaural cue to localisation. The bumps and ridges on the pinnae produce reflections, and delays between the direct path and the reflected path make vertical localisation possible. Vertical localisation is seriously impaired if the convolutions of the pinnae are covered.


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11.2 Frequency discrimination

Some findings indicate that, for moderate loudness levels, humans can detect a frequency change of about 1 to 3 Hz for frequencies up to about 1000 Hz. Figure 37 shows a plot of the smallest frequency difference for which two tones can be discriminated for a number of reference tones. You can see from the figure that up to about 1000 Hz, the D
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6.3 Summary of Sections 4 to 6

Hair cells do not have axons and therefore do not generate action potentials.

The nerve that communicates with or innervates the hair cells along the basilar membrane is known as the vestibulocochlear nerve or VIIIth cranial nerve. The cochlear portion of the nerve contains afferent fibres that carry information in the form of action potentials from the organ of Corti to the brain, and efferent fibres that bring information from the cerebral cortex to the periphery.

Most of the af
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5.1 Place code

We know that each hair cell occurs in a localised region of the cochlea, and that auditory nerve fibres contacting each hair cell fire action potentials in response to movement of the basilar membrane at that location. This means that the response of any given fibre should reflect the frequency selectivity of that location on the basilar membrane from which it comes. In other words, cochlear nerve fibres preserve the frequency selectivity found along the basilar membrane. Fibres on the outsid
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3.8 Revision questions

Question 1

Discuss the two ways in which the middle ear increases the effectiveness with which sound is transmitted from the external ear to the inner ear.

Answer
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3.4 The organ of Corti and hair cells

We have established that the vibration patterns of the basilar membrane carry information about frequency, amplitude and time. The next step is to examine how this information is converted or coded into neural signals in the auditory nervous system. To do so, we must look at the organ of Corti in some detail since it is here that the auditory receptor cells that convert mechanical energy into a change in membrane polarisation are located.

As we saw in
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Summary

The ear is made up of the outer, middle and inner ears. The outer ear consists of the pinna, the external auditory canal and the tympanic membrane. The middle ear is air-filled and contains the middle ear ossicles. The inner ear is fluid-filled and contains the cochlea, the semicircular canals and the vestibule.

Sound in the external environment is channelled into the auditory meatus by the pinna and impinges on the tympanic membrane causing it to vibrate. These vibrations are transmitt
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4.4 Incorporating substantial equivalence into national and international law

The concept of substantial equivalence very quickly became important in international trade law. The WTO aims to harmonise national food standards to meet international norms. Under its rules, a country could be penalised if it imposed food standards more stringent than those agreed internationally. In this context, international food standards are set by the Codex Alimentarius Commission (Table 1). In 1996, a report was issued within the Codex framework, which endorsed the principle of subst
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3.2 Communicating Pusztai's findings

In mid-1998, the Rowett Institute released a succession of press releases describing Pusztai's findings. The safety, or otherwise, of GM foods was a hot issue at the time and his preliminary findings gained widespread publicity. Pusztai gave an extended interview to the World in Action TV programme ‘Eat up your genes’, broadcast in August 1998. He described some of his experiments and outlined his interpretations in ways that helped shape the general tone of the programme, which was highl
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3.1 Pusztai's experiments

Issues of ‘fairness’ and our obligations to the developing world do not in themselves explain why the issue of GM plants attracts such controversy. This section focuses on an episode in the fraught history of the development of GM foods that had a significant effect on public attitudes in the UK. In particular, we look at the experiments of Arpad Pusztai in the late 1990s at the Rowett Institute near Aberdeen, Scotland. These experiments are of particular interest to us because they revea
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2.4.1 The second generation of GM crops

Much of the present-day debate about GM plants centres around the existing range of GM crops, most of which have been engineered for herbicide tolerance or insect resistance (covered in unit S250_1 Gene manipulation in plants). One of the implications of this narrow commercial focus is that the benefit that such crops would bring, other than to those multinational companies that produce them, is by no means clear. Weighing up their value on some form of ethical scales might be unlikely
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2.2.1 Do GM crops pose unique problems?

It is perhaps overly simplistic to take the line that only ‘natural foods’ should be commended and that GM plants are unnatural. Arguably, very few of our modern foodstuffs can be termed ‘natural’, in that they are not derived from naturally evolved crops. Tremendous changes in genetic make-up have been achieved by conventional (i.e. non-GM) breeding methods. Traditional plant breeding involves selection of individuals seen as superior, and then crossing, i.e. transferring the pollen
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