1.1 Constructing the H–R diagram

Three properties which are suitable for comparing stars are temperature, luminosity and radius. However, we don't need all three.

Question 1

Why not?


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Learning outcomes

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

  • define and use, or recognise definitions and applications of, each of the bold terms;

  • provide examples that show there is a continuum of desert climates and environments that link to diversity of flora and fauna;

  • explain, with examples, the thermoregulatory strategies of evaders, evaporators and endurers, and interpret relevant data;

  • describe the importance of integration of behavi
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Introduction

This unit is the first in a series of three on Animals at the extreme. It is concerned with the integration of behaviour anatomy, physiology and biochemistry in diverse vertebrates that live in deserts. Once you have completed this unit, you will be all the more able to appreciate the linked units that follow, Animals at the extreme: hibernation and torpor and Animals at the extreme: the polar environment. These units build on and develop some of the science you will stud
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6.7 Sleep, the brain and hibernation

There has been a popular misconception that hibernating animals are asleep when dormant, and that arousal during or at the end of hibernation involves waking analogous to that following deep sleep. Sleep in homeothermic animals can be divided into several phases, each with distinct patterns of electrical activity in the brain, as measured by an electroencephalogram (EEG). The passage into sleep is a transition from wakefulness into the stage called slow-wave sleep (SWS). SWS, and its c
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6.3 Metabolic regulation and the midbrain

As you found in the last section, the physiological evidence points to the likelihood that different components of regulation may be regulated separately. The hypothalamus, which appears to be central to the depression and recovery of body temperature during entry to torpor and arousal, is not the only player in the control of metabolic processes underlying non-behavioural thermogenesis. In many respects, the initiation of thermogenesis is the prime event in the reactivation of a cold body: t
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4.2 Arresting protein synthesis

The regulation of T b in hibernators has traditionally been viewed as the fundamental physiological process in hibernation. But recently, questions have been raised about whether thermal changes initiate or simply accompany metabolic depression. Is the metabolic inactivity of animal tissues during bouts of torpor or in hibernation, the cause or the result of hypothermia? A common-sense view is that temperature directly influences metabolism by regulating enzyme activity. Evi
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3.5.1 Final arousal

Emergence can be viewed as the final step in the series of periodic arousals. Instead of re-entering hibernation, the animal maintains the euthermic condition. The cue for maintaining this final arousal is probably not temperature, as some species emerge when T a is well below zero. It is also difficult to see how arousal could be affected by daylength, since the hibernating animal is usually underground in a cavity or a burrow. Perhaps fat or food stores reach a minimum lev
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3.3 Maintenance

Entering hibernation is not a passive process in response to falling T a. Nor is deep hibernation a passive process or indeed a uniform state. Figure 13 shows the pattern of hibernation (as measured by the heart rate) of an arctic marmot (Marmota caligata) kept in the laboratory at a T a of 10° C for 18 days in February. Despite being inactive, every one or two days the heart rate rises abruptly, remains high for a number of days, and then falls ag
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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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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:

Unit Image

Chaserpaul

All other materials included in this unit are derived from content originated at the Open University.
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1.1.1 The chemical structure of DNA

This unit explores the chemical nature of the genome. Genomes are composed of DNA, and a knowledge of the structure of DNA is essential to understand how it can function as hereditary material. DNA is remarkable, breathtakingly simple in its structure yet capable of directing all the living processes in a cell, the production of new cells and the development of a fertilized egg to an individual adult.

DNA illustrates beautifully the precise relationship between molecular structure and b
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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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Introduction

Genomes are composed of DNA, and a knowledge of the structure of DNA is essential to understand how it can function as hereditary material. DNA is remarkable, breathtakingly simple in its structure yet capable of directing all the living processes in a cell, the production of new cells and the development of a fertilized egg to an individual adult.

DNA has three key properties: it is relatively stable; its structure suggests an obvious way in which the molecule can be duplicated, or re
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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:

Unit Image

Chase Crowson flickr.com (18 October 2007)

All other materials included in this unit are derived from content originated at the Open University.


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3 The flow of information from DNA to RNA to protein

The information flow from DNA to protein is more complex than shown in Figure 1. The genetic information encoded within the DNA of a gene is carried via an intermediary molecule, RNA (ribonucleic acid). Information within a cell can therefore be seen as passing from DNA, via RNA, to a protein. This flow of information can b
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1.4 Broadly typical phases of PhD research

A modern PhD can be viewed as having three key phases (very roughly, but not strictly, corresponding to the three years of a full-time degree), each of which contributes a necessary element of mastery:

  1. Orientation – mastering the literature and formulating a research problem and plan.

  2. Intensive research – gathering the evidence to support the thesis, whether empirical or theoretical.

  3. Entering t
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1.3 Different models of PhDs within and across disciplines

There are many different models of how a PhD might be conducted. The models are shaped by the expected place of study (e.g. on the OU campus, in an industry laboratory, at the kitchen table), by the intensity of study and focus (e.g. full time, part time), by the number of influences on the research (e.g. student directed, part of a larger research project, part of an industry research programme), by the level of intended guidance (e.g. taught introduction, supervision-as-collaboration, large
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1.1 Thoughts on a PhD

Entering students often think of a PhD as a ‘magnum opus’, a brilliant research project culminating in a great work. This is rather a demanding model, and few students win Nobel Prizes as a result of their doctoral studies. More realistically, a PhD is research training leading to a research qualification. The PhD is a passport to a research career.

There are other views of a PhD, as well. Getting a PhD can be a ‘rite of passage’, prerequisite to admission into the academic ‘t
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2.2 Why study ecology?

These days, bird watching is a popular leisure activity and in the past so were collecting insects, wild flowers and birds’ eggs (although such activities are not now recommended – indeed, they are often illegal – because of the potential damage they cause to flora and fauna). Some amateurs are or were truly experts in their fields. In fact, much of the original identification of the British flora and fauna was done by amateur naturalists. Many a Victorian vicar or other self-taught nat
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1.11 Summary

Rocks are classified into three types according to how they were formed. Igneous rocks are formed by crystallisation from the molten state; sedimentary rocks are deposited at the Earth's surface from water, air or ice; and metamorphic rocks are rocks of any origin that have been subsequently transformed (metamorphosed) by heat and/or pressure, often several kilometres below the Earth's surface.

Rocks are generally either crystalline, i.e. formed of interlocking mineral crystals, or frag
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