Flashcards in Surviving The Cold Deck (78):
Roughly how much does the temperature drop with every 1000m rise in altitude?
6.5 degrees c.
How might enzyme structural changes influence metabolic reactions?
Any changes might slow down or speed up the reactions.
As the term implies, thermoregulation is a process (consisting of many related processes!) by which organisms maintain their internal temperature within their optimum range for survival. They achieve this by constantly balancing heat loss with heat gain.
Why do organisms need enzymes? What effect can temperature change have on enzymes?
Living organisms rely on enzymes to control metabolic reactions or, in the case of heterotrophs, also to digest macromolecules. Changes in temperature, either increases or decreases, can affect the structural integrity of the proteins that control biochemical reactions and/or the fluidity of biological membranes.
State of controlled lowered body temperature and metabolic rate.
Controls temperature through internal means such as muscle shivering or increased metabolism (e.g. birds, mammals, some plants, some reptiles, fish and many insects).
Which organisms are ectothermic?
Gains heat from external sources (e.g. plants, fungi, amphibians, lizards, snakes, turtles, many fish and most other invertebrates, such as crustaceans).
What is homethermic?
Maintains a stable temperature irrespective of the external environment.
The organism’s temperature is highly variable and tends to respond to that of its environment.
Is a hummingbird Endothermic, Ectothermic, Homeothermic or Poikilothermic (a) during the daytime and (b) at night?
(a) In the daytime a hummingbird is endothermic; (b) at night it is poikilothermic.
Is a marine invertebrate that lives in a constantly stable water temperature Endothermic, Ectothermic, Homeothermic or Poikilothermic?
The animal can be described as both ectothermic and homeothermic. However, if it lived somewhere with a variable water temperature, its body temperature would vary, therefore changing the latter description to poikilothermic.
What features do small animals have that put them at a disadvantage in relation to thermoregulation?
Small animals have large surface area to volume ratios, resulting in high rates of heat loss. They also have high basal metabolic rates (BMR) and a reduced capacity for internal energy storage and hence, additionally, minimal insulation in the form of adipose tissue (fat, i.e. lipid stores).
The regulation of body temperature within a limited range (but not as narrow a range as in homeothermy), independently of ambient temperature by switching between strategies and utilising torpor.
What is the thermoregulatory pathway for birds and marsupials throughout their life stages.
Young are Poikilothermic and progress to heterothermy in adulthood.
The process of producing heat in human or animal body tissues, although thermogenesis also takes place in some plants.
Physiology is the study of the functions of living organisms and their systems.
What special features do you think might enable animals that live on ice floes or in cold waters to avoid experiencing physical damage to their extremities? (Frostbite)
waterproofing, insulation (fur, feathers, adipose tissue pads) or thickened skin, even the use of natural antifreeze compounds. These are all features used by various organisms. A number of mammals and birds also have more specialised circulatory features (covered in Section 3.2.2) which allow them to spend longer periods of time in closer contact with their cold environments.
Define metabolic rate.
The amount of energy used by an organism in unit time. An organism’s energy utilisation per unit time, including overall biochemical activity of the tissues, thermogenesis, movement, digestion, growth, etc. There are many ways of measuring metabolic rate, and hence many different units used to express it, of which the most basic is watts (W).
Define sympathetic nervous system
Part of the autonomic system which controls many involuntary processes (e.g. the gut and the cardiovascular and respiratory systems). Nerves carry signals from the sympathetic system using neurotransmitters such as noradrenalin.
Homeostasis describes the means by which various physiological systems restore the normal functioning of certain key variables within specific limits, after disturbance, by causing responses (signals or feedback) that return the system to its optimum state. Use the example of temperature regulation to explain a negative feedback response.
A control mechanism reacts to a change in the output of the system by initiating a restoring action. If the brain receives a message to inform it that body temperature is not optimum, it then triggers action that will result in a body that is too hot being cooled (e.g. by sweating) or a body that is too cold being warmed (e.g. by shivering) These subsequent changes are fed back to the brain, negating the effects of the original, non-optimum situation and restoring body temperature to the optimum value. Because negative feedback systems maintain a pre-set state, they are stabilising, and therefore an important feature of homeostasis.
how can a plant can regulate its water status in response to perceived drying of the soil but before any dehydration of the plant has occurred.
The roots detect the drying soil and use the chemical messenger, abscisic acid (ABA) to close the stomata in the shoot or leaf to reduce water loss even before the shoot or leaf has experienced any change in water status. This again is a feed-forward response.
Give examples of physiological adaptations and behavioural responses to the cold.
insulative, i.e. increase of subcutaneous (under the skin) fat layer
circulatory adjustments to decreased skin temperature.
metabolic, i.e. shivering or non-shivering heat production, which are both examples of thermogenesis.
Give examples of short term changes in response to the cold
Short-term changes in response to cold include homeostatic and behavioural adjustments. Torpor and hibernation can also be viewed as short-term responses/adaptations.
Explain the process of shivering.
Most terrestrial vertebrates (and certain other animals) can increase thermogenesis by shivering. Their muscles perform mechanically useless movements, but in doing so generate heat which warms the muscles and, eventually, the rest of the body. Shivering is, in a sense, ‘metabolically inefficient’ as the cellular energy stores are used for warming rather than for other processes.
What methods are employed by animals to store extra nutrients for survival in the colder weather?
External caches of food (for example squirrels burying nuts) or subcutaneous layers of blubber (for example baby seals)
Outline the difference between torpor and hibernation.
Torpor is a short-term reduction of body temperature on cool days. Hibernation is an extended form of torpor. Torpor is driven by ambient temperature and food availability; hibernation is associated with day length and hormone changes.
Outline the longer term changes employed by organisms in response to cold.
Adaptations to cold also include external and internal structural changes such as modifications of the form and density of the body hair, circulatory changes and/or metabolic generation of heat by specialised tissues.
Outline the survival strategy of the rock ptarmigan in the Arctic. What changes does the bird undergo in winter?
In preparation for winter they build up a thick layer of subcutaneous adipose tissue over the breast which acts as both insulation and an energy store. It also develops a thick white winter plumage to camouflage against the snow. It moves less in winter but burns the same calories as in the active summer months when it is lean and brown.
What major areas of a typical marine mammal are not protected by blubber?
You may have suggested that the head or flippers (limbs) or tail have minimal coverage of blubber.
Explain the countercurrent heat exchange
A countercurrent exchanger consists of a pair of channels lying in close proximity that contain fluids (or gases) flowing in opposite directions, e.g. where heat loss from the body core to the extremities is minimised by heat transfer between adjacent blood vessels before reaching the outer body surfaces.
What adaptations are found in the respiratory systems of animals which live in cold conditions?
In cold environments, species such as reindeer have elaborately folded nasal turbinals (soft, vascularised tissue supported by fine webs of bone), which warm the air as they inhale, and cool it as they exhale, thereby conserving both heat and water.
What is the gigantic Titan arum? Detail the biological process which makes it famous.
The corpse-flower. A giant bloom which uses thermogenesis. The plants use their stored energy reserves in a biochemically similar process to that in mammals warming themselves by ‘uncoupling’ mitochondrial respiration from ATP production. This process releases the stored energy as heat which, in the arums, is then used to volatise (i.e. vaporise) aromatic compounds to attract pollinating flies or beetles.
Define non-shivering thermogenesis.
Often used synonymously with thermogenesis (generation of heat) in brown adipose tissue. Strictly, NST includes all metabolic thermogenesis except that produced by shivering.
in a few sentences, describe the temperature changes from the external to the internal environment in an arctic fox.
In temperatures of around -10 degrees c the level of warmth increased dramatically in the course layer of fur; increasing to about 35 degrees at the epidermis. There is a further slight and gradual increase throughout the dermis and body tissue to reach a core temp around 38 degrees.
How is absence of predators integrated with capacity for fattening?
Without predation, agility and fast running are not necessary, so being heavy and slow are not maladaptive.
Explain how the shorter legs in R. t. platyrhynchus (Svalbard reindeer) are adaptations to the climate and to the biological environment.
Long, narrow appendages, including legs, have a large surface area over which they lose a lot of heat. Shortness of legs, as well as longer, thicker fur, is an adaptation to the cold climate. Long legs enable fast running, but their growth requires protein and minerals, so the reduction of this energetically expensive character is adaptive in a subspecies that is not subject to predation.
What three elements make up the macronutrient compounds of the major food groups?
Oxygen, hydrogen and carbon.
What are the lipids that store energy called and what are they made up from?
The lipids that store energy are the triacylglycerols (TAGs). TAGs are made up of three fatty acid molecules combined with one molecule of glycerol. The fatty acid chains tend to be of different lengths; the longer the chain, the more carbon-to-carbon bonds are present, and the more energy the molecule has stored within it.
What purpose do the TAGs in seeds serve?
To provide a store of energy needed to allow growth to resume when the seed germinates.
What are TAGs?
Triacylglycerols (TAGs) are often found in the seeds of plants (as oils) and in animals in the adipose tissues of the body. Energy storage.
Why are TAGs more efficient energy storage than glycogen?
The hydrophobic properties of TAGs enable them to be ‘packed’ closely together without associated water. In contrast, the carbohydrate storage molecule, glycogen, is always associated with large amounts of water, making it both bulky and heavy.
The splitting of triacylglycerols into free fatty acids and glycerol by the action of a lipase enzyme (e.g. hormone-sensitive lipase HSL, lipoprotein lipase).
What is WAT?
White adipose tissue (WAT) occurs most extensively in mammals, birds, reptiles and amphibians. WAT is unique to vertebrates, though some invertebrates, notably insects, have a structure known as a ‘fat body’ that has similar biochemical properties. In amphibians and most reptiles, WAT occurs in a few, although relatively large depots, often in the abdomen or in the tail.
What is the distinctive feature of white adipose tissue structure?
The distinctive feature of WAT is a unique type of cell called an adipocyte, which can incorporate much larger quantities of storage lipids than any other kind of cell. As far as animal cells go, adipocytes are always large, but the range of sizes of these cells differs between species.
What is the volume of mature adipocytes in rats and in baleen whales?
In rats, the volume of mature white adipocytes is about 0.02–0.1 nl (nanolitre, 10−9 litre) with a diameter of about 35–60 μm, but in large baleen whales, adipocytes can have a much greater volume: more than 3 nl, with a diameter of around 180 μm, making them among the largest of all mammalian cells.
Outline the structure of adipocytes.
A large single lipid droplet takes up most of the cell. Nucleus are small and squashed against the cell membrane, mitochondria are usually too small to be detected with light microscopy.
Explain the mechanisms of fat growth in obese animals (or humans)
The primary physical difference between an obese person and one of healthy weight is the size of their adipocytes, which is determined by the quantity of TAGs stored within them. Thus, WAT expansion in animals is due mainly to adipocyte enlargement, not to adipocyte proliferation.
What is BAT?
Brown adipose tissue (BAT) is unique to mammals. It is a tissue that is specially adapted to generate additional heat, when the heat released as a by-product of other metabolic processes is not enough to maintain body temperature.
What are the main structural and compositional differences in BAT compared to WAT?
Brown adipocytes are always smaller than mature white adipocytes of a well-fed animal, and usually less than 50 μm in diameter. They contain less TAG than those of white adipose tissue, holding only about 20–30% lipid by mass of the cell compared to 60–90% in WAT. They also have multiple small lipid droplets, not one large one.
How do heterotrophs differ from autotrophs in the way they obtain chemical energy?
Heterotrophs get their energy from organic molecules made by other organisms; they consume and digest the other organisms. Autotrophs make use of the energy from light to synthesise organic molecules which contain energy in chemical bonds.
What is standard metabolic rate?
Environmental temperature changes affect body temperature and the metabolic rate of an ectotherm, so the minimum metabolic rate will be different at various temperatures and is called its standard metabolic rate (at a specified temperature).
Why does the minimum metabolic rate of an ectotherm need to be measured at a specific environmental temperature?
Any changes in the environmental temperature will affect the body temperature, and therefore the metabolic rate of an endotherm, so the minimum metabolic rate will be different at various temperatures and is called its standard metabolic rate.
How do organisms regulate the chemical composition of their internal fluids?
Osmoregulation in plants (Topic 5) was introduced as the process of lowering water potential by accumulating solutes, achieved by a combination of accumulating ions in the vacuole and organic solutes in the cytoplasm. All animals have a similar general requirement, to balance water and solute uptake and loss by controlled solute movement from internal fluids to the external environment.
Measure of the solute concentration of a solution.
Outline the methods of handling waste produce in eggs.
Soluble wastes (i.e. ammonia, urea) can only be excreted from eggs without protective shells; non-toxic semi-solid wastes can be stored and left in hard-shelled eggs following hatching.
What are the different nitrogenous excretory forms?
Ammonia, Urea & Uric acid.
Outline the differences in toxicity between Ammonia, Urea & Uric acid and state the sorts of habitats and organisms in which they are most often employed.
Ammonia is highly toxic and can only be tolerated in low concentrations diluted in water. It is used in aquatic species only. Urea has lower toxicity and requires less water for excretion. Used in land-dwelling organisms with access to water or marine animals which loose water to their environment. Uric acid is the least toxic form and isn't soluble, it is excreted as a paste by land-dwelling animals with limited access to water.
Outline heat generation in BAT during cold exposure.
Brown adipose tissue generates heat without body movement, hence the descriptive term for this process: ‘non-shivering thermogenesis’ (NST). In contrast to NST, heat generation by other metabolic processes is an inevitable by-product and not always beneficial.
Is a hibernating animal homeothermic?
No, not whilst hibernating. Homeotherms maintain a stable body temperature; but hibernators decrease their body temperatures to just above ambient. This is one reason why other, more appropriate, thermoregulatory terms have been developed.
What specialised thermogenic tissue is likely to be involved in the arousal of hibernators?
Brown adipose tissue (BAT), which oxidises fatty acids to rapidly generate heat.
Outline the nutrient and excretory processes undertaken by hibernating animals.
Hibernators typically build up their adipose tissue energy reserves by spending a lot of time feeding before the onset of winter. Only a few species eat food from stored caches on arousal but most take the opportunity to excrete urine and faeces, which suggests that some physiological processes are important enough to need to continue, albeit at a low level, throughout the entire hibernation period.
Under what conditions might it be beneficial to reduce the efficiency of cellular respiration?
When heat production rather than ATP generation is required, such as during hibernation.
What are true hibernators and what is the defining feature of true hibernation?
The particularly defining feature of true hibernation is that hibernators arouse themselves spontaneously throughout the hibernation period, and these arousal episodes are unrelated to the surrounding temperature. True hibernators are small mammals – rodents, bats and insectivores such as the hedgehog.
How many mammals are entirely aquatic?
Only three major orders of mammals are entirely aquatic: whales, seals and sea cows (manatee, dugong), although all other orders except primates, lagomorphs (rabbits and hares) and Chiroptera (bats) have examples of adaptation to an aquatic mode of life.
What sorts of adaptations might enable diving mammals to store large amounts of oxygen (to allow aerobic respiration to continue)?
Any mechanisms that would increase the amount of oxygen stored in the circulatory system or body tissues. Diving mammals have a greater volume of blood as well as higher concentrations of myoglobin (a molecule similar to haemoglobin) which stores oxygen in muscle tissue.
Environment that forms interface between land and water adjacent to rivers and streams.
Suggest what biochemical changes are likely to be taking place within brown adipose tissues of S. palustris (American water shrew) in the few minutes before a dive. How might S. palustris benefit from initiating pre-dive ‘hyperthermia’?
Heat is being generated by non-shivering thermogenesis in BAT.
Warming up before a dive might lead to increased foraging/hunting success rate.
What are some of the different ways in which trophic positions can differ for the same species?
There may be temporal variation (over time, e.g. from autumn to winter) or spatial variation (occurring in different places).
Explain the trophic mismatched hypothesis.
Suggests that the reproduction of predators is more successful at times when this is matched with peak prey availability. It attempts to explain variation within a predator population by relating its phenology to prey species at the next trophic lower level. Thus it is a measure of reproductive success due to how well the phenology of the prey is matched by and able to meet the requirements of its predator.
Recall the function of adenosine triphosphate (ATP) in autotrophs and heterotrophs.
ATP stores energy either absorbed from light via pigments or released from nutrients such as glucose or lipids by the process of cellular respiration. ATP can be thought of as an ‘energy currency’ (like money) which can be made and then spent to get things done. Unlike money, however, large amounts cannot be saved. Each ATP molecule typically exists for only a very brief period – a matter of seconds – before being utilised to provide energy for processes taking place in cells.
How do bumblebees generate the heat required for flight?
Bumblebees use at least two methods to generate the heat required for flight: through shivering of flight muscles and probably substrate cycling in flight muscles.
What is a substrate cycle?
Takes place when two metabolic pathways run in opposite directions simultaneously, catalysed by different enzymes, dissipating energy in the form of heat.
How much energy does 1 mol of ATP free?
What are the four stages involved in the oxidation of glucose in aerobic respiration and where in the cell do they take place?
1. glycolysis, in the cytosol
2. the link reaction, in the mitochondrial matrix
3. the TCA or tricarboxylic acid (or Krebs) cycle, in the mitochondrial matrix.
4. electron transport and oxidative phosphorylation, at the inner mitochondrial membrane.
Outline the process of glycolysis and the link reaction in eukaryotic cells.
In glycolysis, each glucose molecule is broken down into two molecules of pyruvate. In eukaryotic cells, pyruvate enters the mitochondrion where it is broken down to form CO2 and an acetyl group, which is transferred to acetyl CoA. This reaction is called the link reaction because it links glycolysis to the TCA cycle.
Outline the 'uncoupling protein' UCP1
The protein in the inner mitochondrial membrane of brown adipocytes that defines this type of cell. It provides a route for protons to move down their concentration gradient from the outside to the inside of the inner mitochondrial membrane without ATP being synthesised.
How does the uncoupling protein in brown adipose tissue operate?
this protein spans the inner mitochondrial membrane and has the ability to transport protons from one side of this barrier to the other, dissipating the proton gradient. However, in the case of the mitochondria of BAT, this means that protons re-enter the mitochondrial matrix via UCP1 instead of passing through ATP synthase as in all other tissues, and the energy of the proton gradient is released instead as heat.