Tuesday, June 22, 2021
Cold Thermogenesis

Thermoregulation In Plants & Animals, Pyrexia | 12th Biology Ch. 15 Homeostasis | 2nd Year Biology

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Control systems operate in organisms to cope with environmental stresses including temperature
Adaptations in Plants to Low and High Temperature
High Temperature: High temperature denatures the enzymes and damages the metabolism,
therefore, it harms or kills the plants. Plants use evaporative cooling to manage high
temperatures. Hot and dry weather, however, causes water deficiency resulting in the closing of stomata,
thus plants sufer in such conditions. Most plants have adapted to survive in heat stress as the
plants of temperate regions face the stress of 40°C and above temperature. The cells of these
plants synthesize large quantities of special proteins called heat-shock proteins. These proteins
embrace enzymes and other proteins thus help to prevent denaturation.
Low Temperature : In low temperature the luidity of the cell membrane is altered, because lipids
of the membrane become locked into crystalline structures, which afects the transport of the
solutes. The structure of the membrane proteins is also afected. Plants respond to cold stress by
increasing proportion of unsaturated fatty acids, which help membrane to maintain structure at
low temperature by preventing crystal formation. This adaptation requires time because of this
reason rapid chilling of plants is more stressful than gradual drop in air temperature.
Freezing temperature causes ice crystal formation. The coninement of ice formation around cell
wall does not afect as badly and plants survive, however, formation of ice crystals within protoplasm
perforates membranes and organelles hence killing the cells. The plants native to cold region such
as oaks, maples, roses and other plants have adapted to bring changes in solutes composition of
the cells, which causes cytosol to super cool without ice formation, although ice crystals may form
in the cell walls.
Body Heat, Heat Gain and Loss
Temperature of an animal depends upon the rate of change of body heat which in turn depends
on rate of heat production through metabolic processes and the rate of external heat gain and
rate of heat loss. This transfer of heat between an animal and its environment is done in numerous
ways. Principally, infrared thermal radiation and direct and relected sunlight transfer heat into the
animal; whereas radiation and evaporation transfer heat out to the environment.
15. Homeostasis eLearn.Punjab
Temperature Classiication of Animals
Animals deal with variation in the thermal characteristics of their environment. There are animals
in which body temperature tends to luctuate more or less with ambient temperature where air or
water temperatures are changed, these are poikilotherms, all invertebrates, ish, amphibians and
reptiles are considered in this category. The other exposed to changing air or water temperature
maintain their body temperature are the homeotherms and include birds and mammals. Several
diiculties arise with this terminology with studies. It is observed that deep sea ishes maintain
their body temperature due to the constant natural surroundings and lizards regulate their body
temperature; and in contrast numerous birds and mammals vary their body temperature.
Therefore, a more widely applicable temperature classiication scheme is based on the source of heat
production. According to this animals that generate their own body heat through heat production
as by-product during metabolism are endotherms include lying insects, some ishes, birds and
mammals. Ectotherm is the other type, which produce metabolic heat at low level and that is also
exchanged quickly with the environment, however, absorb heat from their surroundings. Most
invertebrates, ish, amphibians and reptiles are in this category. A third category, heterotherms is
of those animals who are capable of varying degrees of endothermic heat production but generally
do not regulate their body temperature within a narrow range e.g. bats, humming bird etc.
Regulation of Heat Exchange between Animals and Environment
Animals use diferent mechanism for such regulation and these are of structural, physiological and
behavioral nature.
Structural Adaptations: These may be long term changes in sub dermal fatty layer insulation and
pelage. The presence of sweat glands and lungs modiied for panting.
Behavioral Adaptations: These include moving of the animal to an


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