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2 SAQs

Question 1.1

Read the following account and then state which strategy from Table 1.1 it best fits.

While freezing is lethal for most organisms, one group of organisms is unaffected by it. Water-bears or tardigrades (phylum Tardigrada)
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1.5.2 Strategy 4: migration (‘go away’)

About 40% of the bird species that breed in Britain do not spend the winter there but migrate south, some to southern Europe, others much further afield. The swallow (Hirundo rustica), for example, may migrate as far as the Cape of southern Africa. From one perspective, migrants are European species that avoid the northern winter by migrating to a less severe environment. On the other hand, the swallow can also be regarded as an African bird that migrates to northern latitudes to breed
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1.4.3 Freeze tolerance in ectothermic vertebrates

In Britain, the vertebrate class Amphibia is represented by frogs, toads and newts. Amphibians are ectotherms, meaning that they are unable to generate large quantities of heat within their bodies, so their body temperature is close to that of their surroundings. The majority of amphibian species avoid the lethal consequences of being frozen, by digging their way under a large object, such as a rock, or deep into the soil, below the level that is penetrated by frost. There are some species, h
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1.4.1 Deciduous trees

During the winter months, a combination of factors, including lower temperatures, reduced light intensity and shorter days, means that plants can only photosynthesise at a slow rate and for restricted periods. As a result, photosynthesis cannot produce energy as fast as respiration expends it. In addition, water is often in short supply because of freezing, and so plants that do not have adaptations to conserve water, as conifers do, would lose water. Deciduous trees avoid these problems in w
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1.2 Response to winter: understanding at different levels

Winter in a temperate region poses a number of environmental problems for organisms. Most obviously, average temperatures are lower than at other times of year and there are frequent frosts. Frost is highly significant for living organisms because water forms such a large proportion of their body tissues; for the great majority of organisms, freezing of their tissues leads to death. Secondly, because, as shown in Table 1.1, many adult organisms die, go into hiding or migrate in winter, many o
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1.1.1 A diversity of strategies

Faced with an environment that becomes relatively hostile with the onset of winter, an adult organism can, broadly speaking, do one of four things:

  1. It can maintain an active lifestyle, adapting in various ways to the prevailing conditions. The robin (Erithacus rubecula) is an example of such a species; so are evergreen trees.

  2. It can abandon an active lifestyle, adopting an inactive existence for the duration of winter. The hedgeho
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Learning outcomes

After studying this unit, you will be able to:

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

  • identify the four main strategies shown by organisms for coping with winter;

  • appreciate and give examples of the levels and types of explanation used for understanding these strategies;

  • describe ways in which the strategies can be subjected to experimental manipulation;

    <
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Acknowledgements

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Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

Figures

Figure 6a NASA Goddard Space Flight Center/COBE Science Working Group;

Figure 6b Courtesy of NASA/WMAP Science Team;

Figure 7 Courtesy of NOAO.

1. Join the 200,000 students currently studying with
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1.7 The hadron era

Time: 10−5 s to 100 s

Temperature: 3 × 1012 K to 109 K

Energy: 1 GeV to 300 keV

From the time that the temperature fell to about 3 × 1012 K, at about 10−5 s after the Big Bang, stable baryons (protons and neutrons) began to form from the up and down quarks that remained after the annihilation of matter and antimatter.

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Acknowledgements

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Unit Image

Calum Davidson

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

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Learning outcomes

After studying this unit you should know:

  • All objects, irrespective of their mass, experience the same acceleration g when falling freely under the influence of gravity at the same point on the Earth. The weight of an object is the force F g due to gravity acting on the object, and for an object with mass m the weight is given by F g=mg.

  • If the height of an object of mass m changes by Δh, the
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4.2 Earthquake magnitude

The magnitude of an earthquake is a measure of the amount of seismic energy released by it, so it is a quantitative scale. The scale of earthquake magnitude is called the Richter scale. Its development is described in Box 4, Charles Richter and the Richter earthquake magnitude scale. The Richter magnitude
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3 Where do earthquakes occur?

How deep in the Earth do earthquakes occur? Most earthquake foci are within a few tens of kilometres of the surface. Earthquakes less than 70 km deep are classified as shallow-focus. Earthquakes with foci 70–300 km deep are classified as intermediate-focus and those below 300 km are deep-focus (Figure 7). Shallow-focus
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1.2 Earthquake-triggered landslides and tsunami

As well as being highly destructive in their own right, earthquakes can also trigger two other very destructive natural hazards. One of these is a landslide. This is a rapid movement of earth materials down a slope, the materials ranging from huge boulders to soil. Landslides can involve the movement of just a small amount of material or enough to bury whole towns in their path. They can have a number of causes, of which earthquakes are just one. The shock of an earthquake may be sufficient t
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3.5 Inheritance

The adaptive explanation for bright coloration in male guppies given above can only be correct, and can only have evolved by natural selection, if male coloration has a heritable basis. Direct evidence that it is a heritable character is of two kinds. First, a wide variety of decorative guppies have been bred for sale on the aquarium market. Such forms could not have been produced if male coloration were not heritable. Second, if samples of guppies are taken from different Trinidadian streams
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3.4 Variation

Guppies vary in a number of characters; in particular, male guppies vary in the number, size and brightness of the coloured spots that decorate their bodies (Figure 2). This variation can be detected within a single population in a given stretch of stream, but is much more obvious when different populations, from different
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3.2 Number of progeny

Female guppies begin to breed as soon as they become mature at about three months old; they then produce clutches of eggs, most of which become fertilized, at roughly one-month intervals until they die or become too old. Clutches vary in size from one to 40 eggs; the average clutch contains about 10 eggs. Thus, female guppies produce a large number of offspring during their lives, far more than can survive to maturity.

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3.1 Introduction

The purpose of this section is to consolidate your understanding of the theory of evolution through natural selection by looking at a specific example. The guppy (Poecilia reticulata) is a small fish whose natural habitat is small streams in northern Trinidad, but it is also a popular aquarium fish. Male and female guppies are very different in appearance (Author(s): The Open University

Learning outcomes

At the end of this unit you should know that:

  • By biological evolution we mean that many of the organisms that inhabit the Earth today are different from those that inhabited it in the past.

  • Natural selection is one of several processes that can bring about evolution, although it can also promote stability rather than change.

  • The four propositions underlying Darwin's theory of evolution through natural selection are: (1) more individuals are produced
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Introduction

In this unit, we describe the theory of evolution by natural selection as proposed by Charles Darwin in his book, first published in 1859, On The Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life. We will look at natural selection as Darwin did, taking inheritance for granted, but ignoring the mechanisms underlying it.

This unit is from our archive and is an adapted extracted from Discovering science (S103) whic
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