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2.3 Hibernators as eutherms

Hibernating endotherms are not the easiest animals to study. Thus, until the late 1960s many biologists believed that mammalian hibernation was a process in which thermoregulation was simply ‘switched off’, following the receipt of a set of ‘cues’. These cues included a declining T a, a shortening daylength, the extent of body fat and a lack of food etc. With this model, the hibernator essentially becomes an ectotherm whose T b follows the T
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1 Hibernation and torpor: An introduction

This unit examines hibernation, a special form of adaptation that animals can make to the ecological demands of remaining in a chosen habitat in winter. Hibernation is a state which enables energy-efficient survival when ambient temperatures are so low that foraging or simply maintaining normal core body temperature and basal metabolic rate are either energetically too costly or impossible.

Polar endotherms can maintain a high T b even when living actively at sub-zero
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Introduction

This is the second in a series of three units on Animals at the extremes. In order to get the most from it, you should have previously studied Animals at the extremes: The desert environment (S324_1). After completing this unit you might like to complete the series by studying Author(s): The Open University

3.3.1 Dormancy in black and brown bears

The dormant state of bears differs from true hibernation in that the body temperature does not fall below 31–35° C and a major disturbance (such as an intruding biologist) can arouse them to full activity in a few minutes. Dormant bears do not eat, drink, urinate or defaecate, the heart rate drops from 50–60 beats min−1 to 8–12 beats min−1, and oxygen consumption is only 32% of that of actively foraging bears. Nonetheless, the rate of protein turnover, as mea
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4.5.5 Sulfur

Deactivation

The presence of sulfur in the exhaust gas mixture causes a reduction in the activity of the three-way catalyst, particularly for the water-gas shift and steam reforming reactions – processes that are important mechanisms for the removal of CO and hydrocarbons under fuel-rich conditions. Sulfur also decreases the efficiency of NOx removal. The deleterious effect of exposure to SO2 on the catalytic activity of a commercial monolithic cata
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4.5.3 The effect of poisons

The use of catalytic converters was one of the major contributors to the phasing-in of unleaded petrol. Lead in petrol is a severe poison for the catalyst, and there have been many stories, particularly in the early days of the converter, of people disabling the catalyst by misfuelling. Figure 25 shows how the activity
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References

Blakemore, C. and Cooper, A. (1970) Development of the brain depends on visual environment, Nature, 228, pp. 477–8.
Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., Taylor, A. and Poulton, R. (2002) Role of genotype in the cycle of violence in maltreated children, Science, 297, pp. 851–4.
Caspi, A., Sugden, K., Moffitt, T. E., Taylor
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8.3 Lissencephaly

Lissencephaly, literally meaning ‘smooth brain’, is characterised by the absence of sulci and gyri, and by a four-layered cortex, instead of the usual six layers, with the majority of cortical neurons in layer four (Figure 22). Babies born with lissencephaly have a very poor prognosis; the disease proving lethal be
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7.4 Elixirs of the nervous system: neurotrophins

According to Section 7.2 axons obtain an elixir from targets at their synapses.

Confirmation that there is indeed an elixir came from a series of events that reveals how much of science really works. Elmer Bucker, working with Hamburger in the mid-1940s, had removed a limb bud from a chick and replaced it with a tumour from
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5.4 Retinoic acid

The retinoic acid story is both distressing and illuminating. It is distressing because with hindsight it is possible to see how the suffering of many people could have been averted. It is illuminating because we now understand much about how retinoic acid works.

Retinoic acid is a natural product of vitamin A. It had been known since the 1930s that a lack of vitamin A, a vitamin A deficiency, led to fetal abnormalities. Subsequent studies in animals showed that an excess of vitamin A a
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3.1 Introduction

We each begin life with a unique genome. As we grow and develop, we are each subjected to a range of factors that influence the way development proceeds. Most of those factors are common to us all, the intracellular and intercellular signals, hormones, birth, milk. But the precise combination and the range and duration of those factors varies between individuals, such as the duration of gestation or the composition and quantity of a mother's milk, for example. In addition we each undergo diff
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2.9 Iron (Fe)

The ability of blood to carry oxygen is due to the presence of the red pigment, haemoglobin, present in red blood cells. Haemoglobin is a protein formed from four polypeptide chains called globins, in the centre of each of which is a small non-protein part called a haem group (haima is Greek for ‘blood’). Each of the haem groups has an iron atom within it (Author(s): The Open University

1.6.2 Riboflavin (vitamin B2)

Riboflavin or vitamin B2, which was originally known as vitamin G, is found in a wide variety of foods, including milk and dairy products. It is more stable to heat than some of the other B vitamins, but is destroyed by exposure to sunlight. Milk in a glass bottle exposed to sun, loses 10% of its riboflavin per hour. Riboflavin plays a crucial role in the metabolism of carbohydrates and proteins and is involved in many other metabolic reactions in the body.

Although riboflavi
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9 Summary

In this unit you have found out that:

  • The sensation of pain is caused by the release of a chemical (prostaglandin) that stimulates the nerve endings and sends an electrical message to the brain.

  • Pain can be reduced if the formation of prostaglandin can be inhibited.

  • Prostaglandin is formed, from arachidonic acid, in a cavity in the active site of the enzyme cyclooxygenase (COX).

  • Geometrical isomerism can be
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1.4.1 Salicylic acid

The structural formula of salicylic acid, 2.1, looks quite complicated. However, it becomes less daunting if you unpack it a bit. One of the first things to do when confronted with an unfamiliar structure is to check that all the valencies are correct (four for carbon, two for oxygen and one for hydrogen). If any atoms have the wrong valency, it follows that there is a mistake somewhere and the molecule does not exist as drawn. It looks OK for the structure of salicylic acid. You proba
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Learning outcomes

After studying this unit you should understand:

  • the basic composition and structure of DNA;

  • what is meant by complementary DNA base pairing;

  • how base pairing allows a mechanism for DNA replication;

  • the number of DNA molecules within a chromosome.


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1 Using information stored in DNA

One important property of DNA is that it carries genetic information in the simple coding language of just four bases. These bases, which can be arranged in a huge variety of sequences, represent a vast potential store of information. In this unit, we consider how this information is used by the cell. The key structural feature of complementary base pairs, which plays an important role in both stability and replication, is also the basis for how DNA functions as genetic material.

How do
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5 Summary

Section 1 Superconductivity was discovered in 1911, and in the century since then there have been many developments in knowledge of the properties of superconductors and the materials that become superconducting, in the theoretical understanding of superconductivity, and in the applications of superconductors.

Section 2 A superconductor has zero resistance to flow of electric current, and can sustain a current indefinitely. The magnetic flux remains constant in a completel
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2.3 The Meissner effect

The second defining characteristic of a superconducting material is much less obvious than its zero electrical resistance. It was over 20 years after the discovery of superconductivity that Meissner and Ochsenfeld published a paper describing this second characteristic. They discovered that when a magnetic field is applied to a sample of tin, say, in the superconducting state, the applied field is excluded, so that B = 0 throughout its interior. This property of the superconducting s
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References

Castells, M. (1997) The Information Age: Economy, Society and Culture, vol. 2, The Power of Identity, Oxford, Blackwell.
Fiske, J. (1993) Introduction to Communication Theory, London and New York, Routledge.
Fuller, S. (1997) Science, Buckingham, Open University Press.
Gibbons, M. (1999) ‘Science's ne
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