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4.5.4 Phosphorus

Phosphorus is recognised as a potential poison for automotive catalysts. The phosphorus level in fuel is generally very low (2×10⁻⁵ g l⁻¹), but it is present in higher concentrations in engine oils (1.2 g l⁻¹). Phosphorus derived from the engine oil is believed to react with the alumina support, and also to reduce the activity of the noble metal component. This deactivation is particularly important for Pd, with which phosphorus may form an all

4.5.6 Catalyst deterioration: summary

An ability to withstand mild deactivation is built into the design of the catalytic converter. However, severe deactivation could prevent the system from meeting emissions legislation.
The major causes of deactivation are thermal damage and poisoning.
High temperatures may cause sintering of the metals and/or the support; this can be prevented to some extent by the addition of ceria as a structural promoter. Damaging interaction

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:

Figures

Figure 2 Nortier, P. and Soustelle, M. (1987) 'Alumina carriers for automotive pollution control', in Cruecq, A. and Frennet, A. (eds) Catalysis and Automotive Pollution Control, Elsevier Science Publishers;

Introduction

This unit is the third in a series of three on Animals at the extreme. In order to get the most from it you should have previously studiedAnimals at the extreme: the desert environment (S324_1)andAnimals at the extreme: hibernation and torpor

This unit is from our archive and is an adapted extract from Animal physiology (S324) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore other courses we offer in <

Learning outcomes

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

define and use, or recognize definitions and applications of each of the bold terms;
outline the special features of the polar regions as a habitat and list some contrasts between the Arctic and the Antarctic;
describe some effects of daylength on feeding, fat deposition and reproduction in arctic animals;
explain why the environmental controls of appetite, activity level and fecun

1.1 Preamble

This unit is about animals' structural and physiological adaptations to living permanently in cold climates; hibernation, a special response to transient or seasonal cold, is described in the openlearn unitAnimals at the extremes: hibernation and torpor (S324_2). Living in a polar climate involves adaptations of many physiological systems: appetite, diet, energy storage and reproductive habits as well as thermoregulation. In many cases, such changes involve ‘ordinary’ physio

1.2 The polar environment

At high latitudes, the Sun's rays always strike the Earth at a large angle from the vertical so they travel through a thicker layer of atmosphere and are attenuated by the time they reach the ground. Because the Earth's axis of rotation is inclined to its path around the Sun, there are large seasonal changes in daylength and the Sun is continuously below the horizon for a period in winter and continuously above the horizon for an equivalent period in summer. The annual changes in daylength an

2.1 Nutrient budgeting

All plants and animals respond to environmental changes such as the light–dark cycle and temperature, but the impact of the environment on essential physiological processes such as eating, fattening and breeding is more evident and often more finely controlled in polar species than in those that are native to warmer and more equable habitats. Large effects are nearly always easier to quantify and to investigate experimentally, so arctic species offer an excellent opportunity to study the su

2.2 Migration for breeding

Birds do not hibernate, but like reindeer, many species undergo daily or seasonal changes in energy expenditure and appetite, and many of the endocrine changes that are an integral part of true hibernation in other groups. The fact that the preliminary stages of hibernation are widespread among vertebrates may help to explain why true hibernation has evolved several times in distantly related taxa. Instead of hibernating, some species of birds migrate to and from breeding areas, where they ar

2.3 Environmental regulation of breeding

As pointed out in Section 1.1, primary plant productivity occurs for only a few months in the summer, so the reproductive physiology of most arctic animals, particularly herbivorous species, is tightly synchronized with the seasons. On Svalbard (Figure 2b), more than 90% of the reindeer fawns are born in the first week of J

2.4 Variable fecundity

The food supply for most polar species depends on several unpredictable factors so successful breeding is far from certain, even if births are tightly synchronized with the seasons. Maintaining pregnancy and feeding the offspring after birth (or hatching in birds) are energetically expensive. The death of the offspring before its maturity represents an irredeemable loss of ‘reproductive investment’ for the parents, particularly the mother, although the earlier in parental nurturing that t

2.4.1 Summary of Sections 1 and 2

Large seasonal changes in temperature and sunlight dominate primary plant production and hence the food supply. Food intake is regulated by the endogenous seasonal control of appetite, fattening and activity, as well as by food availability. Energetically demanding activities such as breeding and migration are only feasible during a brief period and must be tightly synchronized to season. Greater accessibility of food suitable for chicks makes long-distance migration to and from high arctic r

3.1 Introduction

It is clear from Sections 1 and 2 that seasonal or irregular periods of fasting are an integral part of living at high latitudes, especially for large animals. When people (and many tropical and temperate-zone mammals) lose weight, either because they are eating less or because they are suffering from a digestive or metabolic disorder, protein is broken down in substantial quantities long before the lipid stores are exhausted. Even frequent and vigorous exercise cannot prevent the breakdown o

3.2 Penguins

Penguins (order Sphenisciformes) are an ancient and distinctive group of flightless, short-legged birds that evolved in the Southern Hemisphere, probably around New Zealand, about 65 Ma ago in the late Cretaceous, although the oldest known fossils date from about 45 Ma ago.

At a maximum body mass of more than 40 kg, the emperor penguin (Aptenodytes forsteri;Figure 10a) is the largest living penguin (some fossil species were much bigger) and is found further south than any other v

3.3 Bears

Brown or grizzly bears (Ursus arctos), and black bears (U. americanus) feed throughout the summer on grass, fruit, nuts, fish, small mammalian prey and carrion. In autumn, all brown and black bears fatten rapidly before entering caves or hollow trees where they become dormant for weeks or months. The terms ‘hibernation’ and ‘torpor’ are sometimes used to describe this state in bears. To avoid confusion with true hibernation, this phenomenon is here called ‘dormancy�

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

4.1 Insulation in terrestrial endotherms

For organisms of similar size and shape in a similar thermal gradient, the rate of heat loss from convection is up to 90 times as fast in water as in air, so in temperate climates, aquatic endotherms need much more efficient insulation than terrestrial species. Since seawater freezes at −1.9° C, but the temperature of the air around the Poles can fall below −50° C, the insulation requirements of aquatic and terrestrial polar animals are not very different. Nonetheless, there are impor

4.1 Scientific approaches

Even after many years of research, the phenomenon of hibernation continues to be a mystery to scientists. Despite coming nearer to an understanding of how and why it happens, some fundamental questions remain unanswered. Is there a genetic basis underlying the evolutionary predisposition of animals to hibernate, given its occurrence in many groups of vertebrates and invertebrates? Is the problem of metabolic adaptation in cells separate from thermal regulation which occurs throughout the orga

3.3.1 Mining subsidence

Subsidence is an inevitable hazard wherever underground mining is carried out.
The major factors affecting the extent of subsidence are seam thickness and its depth beneath the surface.
The amount of subsidence can be calculated roughly by using the formula:

Energy is defined as the capacity to do work, and primary energy increased more than tenfold during the 20th century (kinetic energy of tides is conve

1.2.6 Stage 4: Extracting the information

When you are absolutely sure that you know what the diagram or table is all about, start to look for patterns, for discrepancies, for peaks and troughs, for anything unusual. Diagrams and tables are highly patterned information, and they often tell a relatively simple story underneath. Don't get bogged down in the relationship between individual numbers, but look to see whether one relationship is like another, or whether one set of numbers stands out significantly from the rest.

Alexis Sullivan
Sullivan and Dr. Chitwood discuss her recent heart surgery.

UAPD Welcomes New Explosive, Firearm Detection Canine
After eight years on the force and more than 450 assignments, the University of Arizona Police Department retired its first bomb-detection canine, Michael. Taking his place is Toby, a 2-year-old black labrador retriever. Toby is certified by the National Police Canine Association in explosive and firearm detection.