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Metabolism and Survival Sub-Topic2.5 Unit 2: Metabolism and Survival Sub-topic2.5 Maintaining Metabolism Duncanrig Secondary JHM 2015 On completion of this sub-topic I will be able to state that: • Many environments experience a range of conditions which will not support life. • To be able to survive such conditions, organisms have evolved strategies to survive adverse conditions. • One strategy is dormancy which is part of some organisms’ lifecycles. • Dormancy is either predictive (occurs before the onset of adverse conditions) or consequential (occurs after the onset of adverse conditions). • Hibernation in mammals is mostly in response to the onset of winter, with reduced temperature and shorter day length. • Aestivation, usually in summer, is induced by high temperatures or drought. • Some organisms which have small body size but high metabolic rates, e.g. hummingbirds, conserve energy by decreasing physiological activity over night, a process known as daily torpor. • Some organisms survive adverse conditions by relocating to a more suitable (survivable) environment. This is migration. • During migration, is expended to relocate to a more suitable environment. • Techniques have been developed to study long distance migration. These include tagging, radio tracking, capture and release, and direct observation. • It is believed that the ability of animals to follow migratory pathways is a combination of inherited (innate) and learned behaviour. • Extremophiles are organisms that live under conditions which would prove lethal to almost any others. • The extreme conditions are usually those of temperature, pH or pressure. • Key to much of their success are enzymes that are tolerant to the conditions. • Scientists have exploited a thermophillic bacterium to obtain Taq polymerase, which is stable at high temperatures and can be used in PCR. • Some of the species living in hot springs or deep sea thermal vents are chemolithotrophs, meaning that they can generate ATP from inorganic molecules. • Other bacteria metabolise methane and sulphur compounds. Prior Learning Unit (3.2) Biodiversity and the distribution of life An adaptation is an inherited characteristic that makes an organism well suited to survival in its environment/niche. Page 1 of 8 JHM May 2015/ LS 2016 Surviving adverse conditions Organisms respond to changes in their external environment in different ways. In order to survive, organisms need to overcome the pressures of their environment and generate enough energy to complete their life-cycle. When environmental conditions become intolerable, for example extremes of temperature or lack of water, organisms frequently resort to two types of survival mechanism: Dormancy- Have devised mechanisms to survive the condition Migration- Avoid the adverse conditions 1. Dormancy A strategy to survive adverse conditions. It is part of an organism’s lifecycle where metabolic rate is reduced. The development of the organism is temporarily suspended, minimising metabolic activity, saving energy, until the environmental conditions improve. Dormancy can be predictive or consequential. (a) Predictive Dormancy occurs before the onset of unfavourable conditions. For example, decreasing temperature and day lengths are cues in seasonal environments that predict the onset of winter. (b) Consequential Organisms only enter a state of dormancy after they have been exposed to adverse conditions. This enables the organism to react immediately to environmental cues and is usually found in unpredictable environments where conditions may change very quickly. Disadvantage - a sudden change in conditions may result in high mortality rates. Page 2 of 8 JHM May 2015/ LS 2016 Advantage - the organisms can delay dormancy until adverse conditions arise, meaning that they can make full use of the resources available in the habitat for as long as possible. An organism may become dormant in response to changes in the environment or dormancy may be part of its life cycle. There are several different ways in which organisms save energy: (i) Daily torpor Daily torpor is a period of reduced activity in organisms with a high metabolic rate. This allows the organisms to save energy when they would not be able to find food. For example, house mice are active during the night and experience torpor through the day when it would be dangerous for them to be out in the open foraging for food. (ii) Hibernation Used by many organisms to escape cold weather conditions and scarce food supplies. The organism's metabolic activity and body temperature fall. Animals prepare for hibernation by eating lots of food in the late summer and autumn. This builds up a layer of fat which keeps them warm and acts as a food source during the hibernation period. As it emerges from hibernation, the organism's metabolic activity and body temperature increase rapidly. Initially, it metabolises at a higher rate than normal to generate energy for its normal active functions. Hibernation can be either a predictive or consequential strategy. This form of dormancy is commonly seen in mammals such as hedgehogs, bears and dormice. (iii) Aestivation A response to high temperatures or drought. For example, the garden snail and some worms become dormant until moisture levels rise again. The snail retreats into its shell and seals the end and the worm coils up in a pocket of air surrounded by mucus. The lungfish, found in South America and Africa survives drought by burying itself in the mud on the river bed; the mud dries with the fish inside where it is able to survive until the next rainy season. Aestivation is a consequential strategy. Page 3 of 8 JHM May 2015/ LS 2016 Complete the table using the descriptions listed. Description list: Dormancy in response to high temperatures or drought; Period of long-term inactivity in animals; Period of reduced activity in animals with high metabolic rates Term Definition Hibernation Daily torpor Aestivation 2. Migration Organisms can also use behavioural strategies to avoid adverse environmental conditions. During migration an organism expends energy to relocate to a more suitable environment. Migratory behaviour is thought to be influenced by both innate (inherited from parents to offspring) and learned behaviour (gained by experience). A large variety of animals, mammals, birds, fish and insects make long journeys from typically feeding and breeding grounds to over-wintering areas and back again the following year. To improve accuracy in tracking the Page 4 of 8 JHM May 2015/ LS 2016 migratory movements of different species tagging methods are employed in conjunction with capture and release techniques. Tag sending signals to satellite The use of satellite technology allows real- time tracking of an individual. Monitoring has now established that the ability to successfully migrate is most likely to be hereditary. By observing the behaviour of a species of bird which has populations that migrate and others that do not, it was found that after breeding between the two types a significant proportion of the offspring had the ability to successfully migrate. The fact that not all of the offspring received the ability suggests that there is more than one gene involved. It was also found that this inbuilt ability was controlled by a circannual rhythm. The birds have an inbuilt 'clock' that measures time. It is thought to be controlled by day length. Extremophiles These are organisms that exist in conditions which would be lethal to the majority of living organisms. They have enzymes that are extremely tolerant and allow them to survive in environment that would be lethal to almost all other species. The majority of extremophiles are archaea. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles. They are found in many ecological niches, including extremes of temperature, pH, salinity or pressure. Microbes that live in cold environments such as sea ice, and the Psychrophiles Arctic and Antarctic ice packs. Microbes that live in very hot environments such as deep sea Thermophiles vents and volcanic lakes. Alkaliphiles Microbes that live in basic environments such as soda lakes. Microbes that live in very salty environments such as salt lakes Halophiles and salt mines. Acidophiles Microbes that live in acidic environments such as sulphur springs Page 5 of 8 JHM May 2015/ LS 2016 These extremophiles may have the potential for industrial exploitation, including food and biochemical manufacturing, pharmaceuticals, and mining. Although most extremophiles are unicellular, there are a few multicellular extremophiles, including pompii worms. Pompii worms are found in deep sea vents and can withstanding extremes of temperature. Their strategy of survival is thought to be based on a symbiotic relationship with bacteria. The worms produce a mucus coat which feeds the bacteria. The bacteria, which contain enzymes which are able to tolerate wide extremes of temperatures, appear to give a degree of thermal insulation to the worms. One of the main obstacles extremophiles must overcome is ensuring their enzymes do not denature in the extreme conditions in which they live. For example, thermophiles, which are capable of living in regions with very high temperatures, must produce enzymes which can function in temperatures in excess of 50◦C. Extremophiles have provided scientists with opportunities to extract enzymes which are stable at high temperatures. One example is Taq polymerase which is used in the polymerase chain reaction (PCR). This enzyme was
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