Extreme language

I have mentioned a number of terms that describe organisms which grow in or survive extreme environmental conditions. Perhaps I'd better explain these terms a bit more before we go any further. There is an imposing terminology that has been developed by scientists working on different types of organisms and different types of environmental stress. Organisms that grow best under extreme conditions (the conditions for their optimal growth is much higher or lower than the average for most...

Deserts

Drawing Deserts World Map

A desert is defined by its lack of water rather than its temperature. This does not mean that there is no water but that rainfalls, and other inputs of water, are irregular and infrequent. Deserts cover one-third of the Earth's land surface (Figure 2.1). This includes semi-arid areas (annual precipitation of less than 600 millimetres), arid areas (less than 200 millimetres) and hyper-arid areas (less than 25 millimetres). Deserts form in the leeward side of...

The origin of life on earth

The Earth is thought to have formed 4.5-4.6 billion years ago, along with the other planets in our solar system, from a protoplanetary disc of gas and dust surrounding the sun (Figure 7.1). A period of intense bombardment from meteorites, asteroids and other protoplanets, swept up by the gravitational pull of the Earth, would have prevented the formation of life during the early stages. Life is thought to have arisen between 4.0 and 3.8 billion years ago. There is convincing fossil evidence for...

Mountains

Mountains are the only other environments, apart from polar regions, where organisms are exposed to permanent snow and ice. Temperature decreases with increasing altitude due to the thinning of the atmosphere. The air is warmed by the transfer of energy from the sun. As it becomes thinner with increasing altitude, there is less air to absorb this energy and hence it is colder. The temperature decreases by an average of 6.5 C for every 1000 metre increase in altitude. The decrease in temperature...

Bibliography

I used the following as general sources of information and inspiration Campbell, N.A. (1996). Biology, 4th edition. Menlo Park, CA Benjamin Cummings. Encyclopaedia Britannica DVD 2000 1994-2000. Encyclopaedia Britannica, Inc. Madigan, M.T., Martinko, J.M. & Parker, J. (2000). Brock Biology of Microorganisms, 9th edition. Upper Saddle River, NJ Prentice Hall. Postgate, J. (1994). The Outer Reaches of Life. Cambridge Cambridge University Press. Wilmer, P., Stone, G. & Johnston, I. (2000)....

Extending the life box

Extremophiles thrive in extreme environments, while cryptobiotes can survive extreme conditions until more moderate conditions return. There are, however, other responses to extreme conditions. Organisms may avoid the extreme conditions by migrating to more favourable ones. Snow geese avoid the cold of the Arctic winter by migrating south to more moderate conditions. Desert insects avoid desiccation and heat during the day by burrowing into the sand. Some organisms can modify their external or...

Extreme evolution

Like most things in biology, we can only truly understand the nature of extreme organisms and extreme environments in the context of their evolution. The conditions we observe today are but a snapshot in time and the organisms are a product of a long history of change, both in themselves and in the conditions which surround them. Conditions on the early Earth were very different from what they are today. It is in this context that we need to consider the nature of extreme organisms and...

Glossary

Absolute zero-the lowest temperature theoretically obtainable (-273 C) Acanthocephala -a phylum of parasitic invertebrate animals acclimation-a physiological adjustment to a change in a physical factor induced in the laboratory acclimatisation-a physiological adjustment to a change in an environmental factor (in nature) acidophile-an organism that grows best at low pH acidotolerant-an organism that can tolerate low pH but which grows best at a higher pH actinomycetes-a group of bacteria noted...

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Hguri 4.4 The lipids of the membranes of bacterial and eukaryotic cells (top) form a bilayer, while those of archaeal cells (bottom) form a monolayer. Only the lipid component of the membrane is shown. tally different from that of bacterial and eukaryotic cells. In the latter two groups, their membranes consist of two layers of lipid, with associated proteins and carbohydrates. In the archaea, the lipid component of the membrane consists of a single layer (Figure 4.4). A lipid mono-layer is...

Salt lakes and soda lakes

Freshwater never consists solely of water but contains, dissolved within it, other substances from the atmosphere or the soil. Lakes which are fed by water flowing over soils and rocks that contain many easily dissolved minerals can become quite salty. Where the lake is fed by streams and rivers but there is no outlet, evaporation may exceed the water flowing in and the minerals become trapped and concentrated. If the minerals are predominantly chlorides, mainly sodium chloride (common salt)...

Under pressure

There are few situations where organisms are naturally exposed to low pressure, but high pressure is a rather more common hazard than we might expect. Organisms that inhabit rocks and sediments beneath the surface of the Earth are likely to be under pressure (see Chapter 2 in the section 'The underworld'). The study of these organisms is in its infancy. We know rather more, however, about those of the other main high-pressure environment, the deep sea (see Chapter 2, 'The cold deep sea'). The...

Altitude metres

Tigure 8.2 The number of species (species richness) of breeding birds and mammals declines with increasing altitude in the Nepalese Himalayas (redrawn from Begon et al., 1996, who give the source of the original data). amount of solar radiation available to fuel the growth of plants and other photosynthetic organisms. Mountains provide an environmental gradient that occurs without a change in latitude. There are very few organisms that can survive the harsh conditions at the top of high...

Pass the salt

You may like plenty of salt on your food, even though you realise that too much salt is bad for you. In fact, for most organisms, too much salt is fatal. High salt concentrations distort the structure of proteins causing them to stick together so they can no longer remain in solution. This destroys their biological function. Organisms may exclude the extra salt because their membranes prevent the salts from entering their cells. The problem then becomes one of the acquisition and retention of...

The antarctic

Marine Phytoplankton Antarctica

It is the Earth's fifth largest continent, accounting for 10 per cent of its land surface and covering an area of some 14 million square kilometres. It is twice the size of Australia and half as big again as the USA. Surrounding it is the Southern Ocean which covers an area twice that of the Antarctic continent and which isolates Antarctica from other land masses. As might be imagined, while there are some common features to Antarctic environments, there is also a...

The breath of life

You only need to stick your head beneath the bathwater for a minute or so to realise how important breathing is for us. We use the oxygen, which makes up about one-fifth of the air we breathe, to fuel our bodies by burning (oxidising) our food. We cannot do without oxygen for long, but there is a surprising variety of organisms that can and which inhabit environments where oxygen is in short supply or absent altogether. Habitats in which oxygen is at low concentrations (microaero-bic) or absent...

The arctic

Arctic Tundra Map

The problems facing organisms in the Arctic are similar to those of Antarctic organisms. The main features of their environment are cold and the risk of freezing, a short growing season and a restricted supply of free water. The Arctic, however, supports a much richer and more diverse community of organisms than does the Antarctic. The primary reason for this is that the Arctic is an ocean surrounded by land (Figure 2.8), while the Antarctic is land surrounded by ocean. This has a number of...

Info

Alkaline lakes Very alkaline soil Seawater 'Pure' water figure 6.2 The pH scale in relation to some example solutions or environments and some organisms that can live at high pH (alkaliphiles) or low pH (acidophiles). to a more neutral pH. Too much lime, however, is harmful and an alkaline soil can be as bad for plants as an acidic soil. Most plants grow best at a neutral pH (around pH 7). Some, however, grow naturally in soils that are slightly acid (peats and heaths) and should not be limed...

Life in the universe

Earth is the only place in the universe where we know for sure that life exists. Those biologists who study life elsewhere (exobiologists or astrobiologists) have rather little to go on. The only other body in the universe that humans have visited, and from which samples have been returned to Earth, is our moon - which turned out to be a barren place as far as life is concerned. Astrobiologists have had to rely on understand ing the conditions that have made life possible on Earth and then...

What is life

Before we are able to discover life elsewhere in the universe, we must first know what we are looking for. There is no universally accepted definition of life, with ideas on the nature of life changing over the years. Different biologists favour different definitions. A physiological definition sees life as fulfilling a number of functions, such as feeding, growing, metabolising, excreting, reproducing, moving and responding to stimuli. We have already seen how the phenomenon of cryptobiosis...

Avoiding freezing

If a small quantity of pure water is cooled, it does not freeze at 0 C and the temperature may fall to as low as 39 C before the formation of ice crystals commences. This phenomenon is known as supercooling, which refers to the water remaining liquid at temperatures below its melting point. The temperature at which freezing eventually occurs is known as the temperature of crystallisation (or supercooling point). For freezing to occur, the water molecules need to come together to form an ice...

Resistance and capacity adaptation to low temperatures

In environments that are temporarily cold, most organisms show resistance adaptation to subzero temperatures, surviving in a dormant state until conditions favourable for activity and growth return. Plants do not generally grow at low temperatures and most terrestrial animals, and other organisms, enter a state of dormancy or cold stupor and become inactive. Metabolism may slow sufficiently at very low tem peratures for the organism to become cryptobiotic. Some freeze-avoid-ing insects,...

The life box

Just as there are ranges for survival and activity with respect to temperature, the same is true for other environmental variables (such as salinity, conditions of acidity or alkalinity, oxygen concentration etc.). We could measure conditions (temperature, pH, salinity etc.) in the environment adjacent to an organism. If we did this lots of times over the lifespan of the organism, we could determine the range of conditions it has experienced. Some organisms move around, experiencing changes in...

In the depths

Pterobranchia

For those of us who rarely venture on the surface of the waves, it is difficult to comprehend how big the oceans of the world are. They cover nearly three times as much area of the Earth as does the land. The oceans are a three-dimensional habitat. Their average depth is more than 3 kilometres and the deepest parts, the great ocean trenches, reach a depth of nearly 11 kilometres below the surface. This is much deeper than the largest mountains on the land are tall. Life is found pretty much...

Extreme organisms

We have met quite a few extreme organisms during the course of this book. They are found among all the major groups (Kingdoms or Domains) of organisms (plants, animals, fungi, protists, bacteria and archaea). However, within these groups, often only certain species, or groupings of species (phyla or lower taxonomic groupings), have the capacity to survive in extreme environments. Among the microbes, the Archaea are the organisms which can survive the most extreme environmental stresses. Some...

Life without water

Most animals and plants have only a limited ability to survive water loss. Humans may die if they lose 14 per cent of the water from their bodies. Some frogs can lose 50 per cent and some earthworms 83 per cent of their water and still recover. Some organisms, however, can lose more than 95 per cent, or even more than 99 per cent, of their water and enter into a state of anhydrobiosis (life without water) in which their metabolism comes, reversibly, to a standstill. There is a problem, however,...

Cold tolerance in plants

If you are a gardener in an area with cold winters, you will know that most plants do not grow over the winter and survive the conditions in a dormant state. The first cold snap will kill off flowering annuals, which then overwinter as seeds. Early growth in the spring will be destroyed by a late frost and so careful gardeners will cover the emerging shoots of their early potatoes with earth to protect them. Plants are subjected to chilling stress at temperatures in the range 0-15 C and to...

Anhydrobiosis and humans

Although the idea of putting humans into suspended animation is likely to remain in the realms of science fiction, at least for some time to come, anhydrobiotic organisms affect human welfare and research on anhydrobiosis has produced, or has the potential to produce, technologies of use to us. The ability of many microorganisms to survive anhydrobiotically means they can be dispersed through the air. This results in the contamination and spoilage of food and in the spread of disease. Allergies...

Tolerating freezing

In some respects, organisms that survive subzero temperatures by avoiding freezing and supercooling are living dangerously. The supercooled state is unstable. Fatal freezing may result from contact with an ice nucleator, exposure to temperatures below their supercooling point or to temperatures below those at which their antifreeze proteins can prevent ice crystal growth. Since the process of freezing may be the most stressful event associated with subzero temperatures, the ability to tolerate...

The members of the hot club

The ability of birds and mammals to regulate their internal temperature allows them to survive in some hot environments. Other organisms can do so by behavioural or structural mechanisms which allow them to lose, or avoid gaining, heat. Some organisms, however, lack these mechanisms and their lifestyle or habitat means that they have had to join the 'hot club' and survive high internal temperatures. The great majority of organisms live in environments where temperatures are in the range of 0-48...

Temperature and life

Changes in temperature have profound effects on biological processes. In general, the rate at which life processes (such as metabolism, respiration and growth) proceed declines as the temperature decreases and elevates as it increases. This is because high temperatures supply more kinetic energy to reactions than do low temperatures, allowing the reacting molecules to come into contact and to interact more frequently. If the temperature continues to increase, however, it starts to have...

Anhydrobiosis

Figure 3.7 The changes that occur during desiccation and rehydration of an anhydrobiotic animal, such as a nematode. agriculturally important plants to be more drought tolerant. If the mechanisms of survival in anhydrobiotic plants can be understood, it may be possible to transfer these abilities to crop plants, using the techniques of genetic engineering, to allow them to be grown in more drought-prone areas. Anhydrobiotic plants can be divided into two groups on the basis of the rate of...

A little dry history

Through Air Dried Tissue

The history of the study of anhydrobiosis is not a dry topic at all, but an intriguing story involving professional jealousies and matters of life and death. The early history has been told in some detail by David Keilin in his Leeuwenhoek lecture, given to the Royal Society of London in 1958, and much of the following draws on his account. The Leeuwenhoek lecture honours the Dutch scientist Antoni Van Leeuwenhoek, one of the first microscopists. Using his microscopes, Leeuwenhoek made many...