Unit 13 Regulation of Temperature
Key Unit Competence
To be able to explain the importance and ways by which organisms regulate body temperature.
LEARNING OBJECTIVES
At the end of this unit, the learner will be able to:
• Explain the importance of temperature regulation.
• Describe the morphological, physiological and behavioural adaptations to temperature
changes in the environment.
• Interpret data related to the effects of temperature on animal behaviour.
• Describe the responses to cold and hot conditions by endothermic and ectothermic animals.
• Interpret and list the adaptive features shown by plants inhabiting extreme cold and hot
environments.
• Acknowledge the importance of maintaining fairly constant temperatures for efficient
metabolism.
• Explain the role of the brain and thermo receptors in temperature regulation.
• Research using the internet the role of brain in temperature regulation.
• Describe the different processes in which plants minimise overheating.• Design and investigate the effect of temperature.
INTRODUCTORY ACTIVITY
Observe the photos below and answer the questions that follow
a). Show 2 main differences between individual A and individual E
b). How is individual C different from individual D?
c). The individual A is adapted to live in cold environments. Analyze it carefully to identify
any two characteristics that this animal hasd). Which among the animals on the photo adapted to live in hot climates? Justify your answer
13.1 IMPORTANCE OF TEMPERATURE REGULATION
ACTIVITY 1
Aim: To investigate the effect of temperature on enzyme activity.
Materials Required:
1. Water bath
2. Ice
3. Test tubes
4. Thermometers
5. Bunsen burners
6. Cornstarch
7. Distilled water
Procedure:
1. Pour some water into the water baths and set the temperature at 37°C and 60°C.
2. Make a starch solution by adding 1 g of cornstarch to 10 ml of distilled water. Pour the
mixture into 50 ml of boiling water and stir until the solution becomes transparent.
3. Prepare amylase solution by adding 2 ml of saliva to 12 ml of water.
4. Take three test tubes and label as Ice, 37°C and 60°C.
5. Add 4 ml of the starch solution and 4 ml of amylase solution in the three test tubes.
6. Immediately place one test tube in the ice, one in the water bath at 37°C and other at 60°C.
7. Incubate the test tubes for 15 minutes.
8. Take 4 drops of samples from each test tube on a glass plates.
9. Add 1 drop of iodine to each sample.
10. Note the time taken for the iodine to turn yellow from blue.
Discussion:
Amylase is an enzyme that hydrolyzes starch into its components i.e., glucose. Iodine turns blue
when it comes into contact with starch, but it stays yellow in the presence of glucose. Therefore,
faster the iodine turns yellow from its blue colour, the faster amylase works on the starch.
Note the time taken for different samples and discuss the result with your teacher.
Precautions:
1. The temperature of the water baths should be properly set.
2. Starch solution should be homogenous.3. Time should be noted carefully.
Besides water, our body consists of many inorganic and organic compounds including proteins,
lipids, carbohydrates etc. Among these, proteins are the most important compounds and are
regarded as “workhorse” molecules of life, taking part in essentially every structure and activity
of life. Proteins make up about 75 per cent of the dry weight of our bodies and serve fourimportant functions;
1. They are nutritious.
2. They also form the structural components of our body including skin, hair etc. They are
building materials for living cells, appearing in the structures inside the cell and within
the cell membrane.
3. As haemoglobin, Hb they carry oxygen to all the body organs and
4. They functions as biological catalysts as enzymes facilitating and controlling various
chemical reactions of our body.
Protein molecules are often very large and are made up of hundreds to thousands of amino
acid units. They are of varying shape and size. For examples, keratins, a protein in hair and
collagen in tendons and ligaments linear chains of amino acids. Other proteins called globular
proteins, fold up into specific shapes and often more than one globular unit are bound together.
Enzymes are globular proteins. Though large, enzymes typically have a small working region,
known as active site which acts as the binding site of ligands. The shape of globular proteins
is held together by many forces, including highly resistant strong covalent bonds. However,
there are also many weak forces, like hydrogen bonds, which are susceptible to pH, osmolarityand temperature changes.
Since the function of enzymes is attributed to its shape, small changes in the shape can
greatly reduce its function. Every enzyme has an optimal temperature at which it works best
and this temperature is approximately the normal body temperature of the body. Therefore,
in order to ensure the optimal function of the enzymes within, the core body temperature
need to be maintained more or less constant. If the body temperature falls below the normal
value, the enzymes catalyzed reactions of the animal will be slowed. Similarly, too much
rise in body temperature might result in enzyme denaturation and hence reduced catalytic
activities.
Rise in body temperature also reduces the oxygen carrying capacity of haemoglobin. Increasing
temperature weakens and denatures the bond between oxygen and haemoglobin which in turn
decreases the concentration of the oxyhaemoglobin. This can lead to hypoxia – a condition inwhich tissues receive insufficient oxygen supply from the blood.
13.2 MORPHOLOGICAL, PHYSIOLOGICAL AND BEHAVIOURALADAPTATION TO TEMPERATURE CHANGES IN THE ENVIRONMENT
ACTIVITY 2
Use internet to find the pictures of animals living in different temperature conditions like arctic,
snow covered mountains, forest, deserts, sea etc.Use the following link: https://www.youtube.
com/results?search_query=animal+habitat&sp=EgIwAQ%253D%253D
Print the pictures and paste it in your scrapbook.
Write down different morphological, physiological and behavioural adaptations of the
animal which help it to live in a particular environment. Discuss various adaptations of yourcollections.
From deepest corner of the sea to high mountains, living organisms have colonized almost
everywhere. However, they are not distributed evenly with different species found in different
areas. Many abiotic factors including temperature, humidity, soil chemistry, pH, salinity, oxygen
levels etc., influence the availability of species in certain area. Each species has certain set of
environmental conditions within which it can best survive and reproduce to which they are
best adapted. This is known as limits of tolerance (i.e., the upper and lower limits to the range
of particular environmental factors within which an organism can survive). No organism can
survive if the environmental factor is below its lower limits of tolerance or above the higher
limits. Therefore, organisms having a wide range of tolerance are usually distributed widely,while those with a narrow range have a more restricted distribution. For examples, euryhaline
fishes (like salmon) can survive wide range of salt concentration and therefore are found both
in freshwater and salt water environment while stenohaline fishes are found only in saltwateror freshwater.
Temperature is one of the most important factors which directly or indirectly influence the
distribution of organisms to a large extent. For example, polar bears can survive very well in
low temperatures ranges, but would die from overheating in the tropics. On the other hand, a
giraffe does very well in the heat of the African savanna, but would quickly freeze to death in
the Arctic. Compared to ectotherms or cold blooded animals, endotherms due to their ability to
generate their own body heat, are generally more widely distributed. Besides, all the organisms
have varying degree of morphological, physiological or behavioural adaptations that helps themto survive the extreme temperature conditions of their habitat.
13.2.1 Effect of Temperature
As discussed above, all the living organisms have a particular range of temperature within which
they can best survive and reproduce. Temperature below or above this temperature ranges are
harmful to the organism in various ways. Some of well known effects of temperature on livingorganisms are given below.
1. Effect of temperature on cells: If the temperature is too cold, the cell proteins could be
destroyed due to the formation of ice, or as the water is lost, the cytoplasm can become
highly concentrated. Conversely, extreme heat can coagulate cell proteins.
2. Effect on metabolism: Most of metabolic activities of microbes, plants and animals are
regulated by enzymes and the functions of enzymes are greatly affected by temperature.
Therefore, increase or decrease in the body temperature will greatly affect the various
metabolic activities. For example, the activity of liver arginase enzyme upon arginine
increases gradually with increase in the temperature from 17°C to 48°C. With the increase
in temperature beyond 48°C, the enzymatic activity decreased sharply.
3. Effect on reproduction: Changes in temperature affect both the maturation of gonads
i.e., gametogenesis and fecundity of animals. For example, some animal species can breed
throughout the year, some only in summer or in winter, while some species have two
breeding periods, spring and autumn. Therefore, temperature determines the breeding
seasons of most organisms. Also, it was observed that female chrotogonus trachypterus
an acridid insect lays highest number of eggs per female at of 30°C and decreases with
increase in temperature from 30°C to 35°C.
4. Effect on sex ratio: In certain animals like copepod Maerocyclops albidu, rises in
temperature significantly increases the number of male offspring. Similarly in plague flea,
Xenopsylla cheopis, males’ population outnumbered females when the mean temperature
is between 21°C to 25°C. However, further decreases in temperature reverse the conditions
with the considerable increases in female population.
5. Effect on growth and development: In general growth and development of eggs and
larvae is more rapid in warm temperatures. For example, Trout eggs develop four times
faster at 15°C than at 5°C. On the other hand, seeds of many plants will not germinate
and the eggs and pupae of some insects will not hatch until chilled.
6. Effect on colouration: Animals generally have a darker pigmentation in warm and
humid climates than those found in cool and dry climates. This phenomenon is known
as Gioger rule. In the frog Hyla and the horned toad Phrynosoma, low temperatures
have been known to induce darkening. Some prawn turn light coloured with increasing
temperature.
7. Effect on morphology: Temperatures have profound effects on the size of animals and
various body parts. Endotherms generally attain a larger body size (reduced surface-mass
ratio) in colder temperatures than in warmer temperatures. As such the colder regions
harbour larger species. Conversely, the poikilotherms (ectotherms) tend to be smaller in
colder regions. We will discuss the various morphological modifications due to extreme
climates in the later sections.
8. Effect on animal behaviour: Temperature certainly has profound effect on the behavioural
pattern of animals. The advantage gained by certain cold blooded animals through
thermotaxis or orientation towards a source of heat are quite interesting. Ticks locate
their warm blood hosts by a turning reaction to the heat of their bodies. Certain snakes
such as rattle snakes, copper heads, and pit vipers are able to detect mammals and birds
by their body heat which remains slightly warmer than the surroundings.
9. Effect on animal distribution: Since the optimum temperature for many organisms
varies, temperature imposes a restriction on the distribution of species. The diversity ofanimals and plants gradually decrease as we move from equator towards the pole.
13.2.2 Morphological Adaptations
1. Body size and shape: Ectotherms or cold-blooded animals whose body temperature
depends on the temperature of external environments are usually smaller in size compared
to endotherms or warm blooded animals. For instance, compare the size of elephant,
blue whales and crocodiles or snakes. Within the same species, individuals living in thecolder climates tend to be larger than those living in warmer climates. This is known as
Bergmann’s rule. For example, whitetail deer in the southern part of the United States
have a smaller body size than whitetail deer in the for norhtern states (Figure 13.1 (A))the far northern states (Figure 13.1 (B)).
Figure 13.1: Bergmann’s rule: Body size and temperature. White-tailed deer
(Odocoileus virginianus) extend from Canada through Central America into South America north of
the Amazon River basin. There is a strong size gradient, with the largest
animals in the temperate north (A) and the smallest in the warm neotropics (B). Antler growth is
positively allometric with respect to skull size: the smaller animalhas disproportionately small antlers
2. Body Extremities: According to Allen’s rule, animals living in the colder climates have
more rounded and compact form. This is achieved by reducing the size of the body
extremities i.e., ears, limbs, tails etc. On the other hand, animals living in the warmer
climates have longer body extremities. For instance, compare the size of the ear of Arctic
fox with that of the Desert fox (Figure 13.2). Longer body extremities increase the surface
to volume ratio of the desert fox which enable them to lose heat more easily.
Most cold-blooded organisms have either an elongated or a flat body shape. For example,
fishes, snakes, lizards, and worms have long and slender body form which ensures rapidheat up and cool down processes.
Figure 13.2: Allen’s rule: Body extremities and temperature. (A) Arctic fox (Alopax lagopus) with its
short tail, ear and legs and (B) Desert fox (Vulpes chama) with longer tail, ear and legs
Both Bergmann’s rule and Allen’s rule depend on simple principle that “the ratio of surface
area to volume of an object is inversely proportional to the volume of the object”. In other words,
the smaller an animal is, the higher the surface area-to-volume ratio. Higher surface
area-to-volume ratio ensures these animals to lose heat relatively quickly and cool down
faster, so they are more likely to be found in warmer climates. Larger animals, on the
other hand, have lower surface area-to-volume ratios and lose heat more slowly, so andthey are more likely to be found in colder climates.
3. Insulation: All the marine mammals have a thick insulating layer of fat known as
Blubber, just beneath the skin. It covers the entire body of animals such as seals, whales,
and walruses (except for their fins, flippers, and flukes) and serves to stores energy,
insulates heat, and increases buoyancy. Thickness of blubber can range from a couple
of inches in dolphins and smaller whales, to 4.3 inches in polar bears to more than
12 inches in some bigger whales. To insulate the body, blood vessels in blubber constrict
in cold water. Constriction of the blood vessels reduces the flow of blood to the skin and
minimizes the heat loss. In such animals, skin surface temperature is nearly identical
to the surrounding water, though at a depth of around 50 mm beneath the skin, thetemperature is the same as their core temperature.
Some marine mammals, such as polar bears and sea otters, have a thick fur coat, as well
as blubber, to insulate them. The blubber insulates in water while fur insulates in air or
terrestrial environment. The feathers of the birds also function in insulating the bodyfrom cold temperature.
13.2.3 Physiological Adaptations
1. Evaporation: In a colder region, i.e., when the surrounding environment of the animal is
cooler than the body temperature, conduction and radiation are the main ways an animal
will dissipate heat. However, in warmer region, the air temperature is often higher than
the animal’s body temperatures, so the only physiological thermoregulatory mechanism
available is evaporation. Animals use three evaporative cooling techniques that includesweating, panting, and saliva spreading.
(a) Sweating: It is the loss of water through sweat glands found in the skin of mammals.
The number of sweat glands can vary from none in whales, few in dogs to numerous
in humans. Most small mammals do not sweat because they would lose too much
body mass if they did. For example, in a hot desert the amount of water a mouse
would lose through sweating to maintain a constant body temperature would be
more than 20% of its body weight per hour, which could be lethal for the animal.
Therefore, smaller mammals use other techniques to cool down their body. On the
other hand, sweating is an important thermoregulatory mechanism for primates
including humans. An adult human can loss as much as 10–12 litres of water per
day through sweating.
(b) Panting: It is rapid, shallow respiration that cools an animal by increased evaporation
from the respiratory surfaces. It is a common thermoregulatory technique used by
small animals like dogs and rodents to loss heat.
(c) Saliva spreading: It is a means of thermoregulation used by marsupials. Under
extreme heat, saliva will drip from animal’s mouth and is then wiped on its fore and
hind legs. This technique induces the cooling effect of evaporation by wetting the fur.
However, since the animal cannot spread saliva while moving, they need to adapt
other evaporative techniques during such situations.
2. Counter current mechanism: As mentioned above, in addition to its role in the transport
of oxygen and food, circulatory system of our body is responsible for distribution of
heat throughout the body. This is true in case of both endotherms and ectotherms.
In endotherms, most of the body heat is generated in brain, liver, heart and skeletal
muscles. This heat is transported to other parts of the body through blood. On the other
hand, in ectotherms, the circulatory system help in transporting heat from skin to others
body parts. The counter current heat exchanger is generally located in body extremitieslike limbs, neck, gills, which are directly in contact to the external environment.
In colder region, when the warm blood flows through the arteries, the blood gives up
some of its heat to the colder blood returning from the extremities in the veins running
parallel to the arteries. Such veins are located in the deeper side of the body and carry
the warm blood to the heart and most of the body heat is retained. Such mechanism
can operate with remarkable efficiency. For instance, a seagull can maintain a normal
temperature in its torso while standing with its unprotected feet in freezing water(Figure 13.3).
When the external temperature is higher than the body temperature and heat loss is not
a problem, most of the venous blood from the extremities returns through veins located
near the surface. If the core body temperature becomes too high, the blood supply to
the surface and extremities of the body is increased enabling heat to be released to thesurroundings.
Figure 13.3: Counter current heat exchange mechanism. As warm blood travels from the heart to
the gills, an exchange of heat takes place with the colder blood returning from the gills
3. Hyperthermia: Hyperthermia is a condition of having the body temperature greatly above
the normal. Although all the endotherms can maintain a constant body temperature, some
are able to raise their body temperature as a way to decrease the amount of water and
energy used for thermoregulation. For example, camels and gazelles can increase their
body temperature by 5–7°C during the day when the animal is dehydrated. Hyperthermia
helps in saving water by letting their body temperature increase instead of using evaporative
cooling to keep it at a constant temperature.
4. Water retention: Human body obtains about 60 per cent of the water they need from
ingested liquid, 30 per cent from ingested food, and 10 per cent from metabolism. While
rodent adapted to arid conditions obtains approximately 90 per cent from metabolismand 10 per cent from ingested food. The predaceous marsupial Mulgara can go its whole
life without ingesting water but by obtaining water from the food they eat and from
metabolism. The fawn hopping mouse eats seed, small insects, and green leaves for
moisture, and Kowaris eat insects and small mammals to obtain water. These animals
have specialized kidneys with extra microscopic tubules to extract most of the water from
their urine and return it to the blood stream. And much of the moisture that would be
exhaled in breathing is recaptured in the nasal cavities by specialized organs.
Many desert dwelling insects tap plant fluids such as nectar or sap from stems, while
others extract water from the plant parts they eat, such as leaves and fruit. The abundance
of insects permits insectivorous birds, bats and lizards to thrive in the desert. Elf owls
survive on katydids and scorpions. Pronghorns can survive on the water in cholla fruits.
Kit foxes can satisfy their water needs with the water in their diet of kangaroo rats, mice,and rabbits, along with small amounts of vegetable material.
5. Excretion: As mentioned above, desert dwelling mammals and birds have specialized
kidneys with long loops of Henle compared to animals that live in aquatic environments
and less arid regions. A longer tubules help in reabsorbing most of the water from their
urine and return it to the blood stream. As a result, the urine becomes highly concentrated.
In these animals, most of the water in the faeces gets reabsorbed in the alimentary
canals and colon. Camels produce dryer faeces than other ruminants. For example, sheep
produce faeces with 45 per cent water after 5 days of water deprivation, while camels
produce faeces with 38 per cent water even after 10 days of water deprivation. The ability
to excrete concentrated urine and dry faeces is an important adaptation to arid conditions.Desert rodents can have urine five times as concentrated as that of humans.
13.2.4 Behavioural Adaptations
Behavioural adaptations are used to reduce the amount of heat gained or lost by animals, and,
thereby, reducing the amount of energy and water to maintain the body temperature. Ectodermsor cold blooded animals rely on their behaviour to maintain a favourable body temperature.
1. Nocturnality: It is the simplest form of behavioural adaptation characterized by activity
during the night and sleeping during the day. As such, nocturnal animals avoid direct
exposure to heat of the day, thereby preventing loss of water needed for evaporative
cooling. The night temperatures are generally 15–20°C colder than the daytime, so require
much less energy and water to regulate body temperature. Most of the desert animals
like quoll, bilby, and the spinifex hopping mouse, are nocturnal. Other large animals likelions prefer to hunt at night are to conserve water.
Crepuscular animals are those animals that are mainly active during twilight (i.e., the
period before dawn and that after dusk). Examples include hamsters, rabbits, jaguars,
ocelots, red pandas, bears, deer, moose, spotted hyenas etc. Many moths, beetles, flies,
and other insects are also crepuscular in habit. These crepuscular animals take advantage
of the slightly cooler mornings and evenings to escape the daytime heat, and to evaporateless water
2. Microhabitat: Among the diurnal animals (animals which are mainly active during the
day and rest during night), the use of microhabitat like burrows, shade is another type of
behavioural adaptation to avoid the daytime heat. Fossorial animals (digging animals),
such as mulgaras, spent much of their time below ground eating stored food. Lizards
and snakes seek a sunny spot in the morning to warm up their body temperatures morequickly and remain in shade when the temperature rises.
3. Migration: It is the physical movement of animals over a long distance from one area to
another. It is found in all major animal groups, including birds, mammals, fish, reptiles,
amphibians, insects, and crustaceans. Many factors like climate, food, the season of the
year or mating could lead to migration. It helps the animals in avoiding the extreme
environmental conditions by moving to more favourable places. For example, many
migratory birds like arctic tern (Sterna paradisaea) migrate north-south, with species
feeding and breeding in high northern latitudes in the summer, and moving some hundreds
of miles south during the winter to escape the extreme cold of north. Monarch butterflies
spend the summer in Canada and the Northern America and migrate as far south asMexico for the winter.
4. Hibernation and Aestivation: Warm blooded animals which do not migrate generally
survive the extreme cold condition of winter by sleeping. Hibernation is the state of
dormancy during the cold conditions, i.e., winter. During hibernation, body temperature
drops, breathing and heart rate slows, and most of the body’s metabolic functions are put
on hold in a state of quasi-suspended animation. This allows them to conserve energy,and survive the winter with little or no food.
Many insects spend the winter in different stages of their lives in a dormant state. Such
phenomenon is known as diapause. During diapauses, insect’s heartbeat, breathing
and temperature drop. Some insects spend the winter as worm-like larvae, while others
spend as pupae. Some adult insects die after laying their eggs in the fall and eggs hatch
into new insects in the spring when the food supply and temperature become favourable.
Aestivation or summer dormancy on the other hand, is a state of animal dormancy,characterized by inactivity and a lowered metabolic rate, in response to high temperatures
and arid conditions. It allows an animal to survive the scarcity of water or food as
aestivating animal can live longer off its energy reserves due to the lowered metabolism,
and reduced water loss though lowered breathing rates. Lung fishes, toad, salamander,
desert tortoise, swamp turtles are some of the other non-mammalian animals whichundergo aestivation.
5. Social behaviour: Among all the adaptations, living together is one of the most important
adaptations of the animal kingdom. Animals can derive a lot of benefit from spending
time with other members of the same species like finding food, defence against predators
and care for their young. For example, emperor penguins can survive the harsh Antarctica
winter huddling together in groups that may comprise several thousand penguins.
Huddling greatly reduces the surface area of the group compared to individuals and a
great deal of warmth and body fat is conserved. Many social mammals, including manyrodents, pigs and primates survive extreme cold by huddling together in groups.
6. Locomotion: Different types of locomotion require varying amount of energy. Many
mammals like kangaroo, hares hop, which is an energy efficient type of locomotion.
When animals go from walking to running, there is an increasing energy cost; however,
once kangaroos start moving, there is no additional energy cost. This is because when a
kangaroo lands, energy is stored in the tendons of its hind legs which is used to powerthe next hop.
APPLICATION 13.1
1. Complete with correct terms:
(i) ................... is a dormant state experienced by many insects during winters.
(ii) Gioger rule states that animals have ................... colouration in warm climate.
(iii) Individuals of some species living in colder climates tend to be larger than those in
warmer climates exhibiting ................... rule.
(iv) Polar bears and sea otters have ................... and ................... for insulation.
(v) Camels and gazelles save water by letting their body temperature .................
2. Why does a mammal have to eat much more food than a reptile of equivalent size?
3. List the three main ways in which heat can be transferred from the environment to an animal4. Suggest why a person who has dry skin in a hot environment might be in danger
13.3 RESPONSE TO COLD AND HOT CONDITIONS BY
ENDOTHERMIC AND ECTOTHERMIC ANIMALS
ACTIVITY 3
Select an animal to study the temperature regulation mechanism.
Study different morphological, physiological and behavioural adaptation of the animals in
different temperature.Make a PowerPoint presentation and present it in the class.
13.3.1 Endotherms’ Response to Temperature Changes
Endothermic organism can maintain relatively high body temperatures within a narrow
range. Since most of the body heat is produced as a result of various metabolic activities,
thermoregulation in endotherms depends on food and water availability. For example, bear
undergoes hibernation during the winter because there is no sufficient food during the cold
season. On the other hand, in arid environment like deserts, many deserts animals are nocturnalto avoid the extreme daytime heat to avoid loss of water through evaporation.
Response to Hot Temperature
When the body temperature increases in response to the external temperature, the body’stemperature control system uses three important mechanisms to reduce the body heat. These are:
1. Vasodilation: The blood vessels in skin become intensely dilated due to the inhibition
of the sympathetic centres in the posterior hypothalamus that cause vasoconstriction.
Vasodilation increases the rate blood flow to the skin and as a result, the amount of heattransfer from the core of the body increases tremendously.
2. Sweating: As discussed in the previous section, sweating is an important adaptation
to lose body heat through evaporative cooling. An increase in 1°C in body temperaturecauses enough sweating to remove ten times the basal rate of body heat production.
3. Decrease in heat production: As mentioned above, metabolic activities of the body are
the main source of body heat. The mechanisms that cause excess heat production, such
as shivering and chemical thermogenesis, are strongly inhibited when exposed to hottemperature
Response to Cold Temperature
In response to cold temperature, the temperatures control system performs exactly oppositemechanism to that performs in hot temperature. These are:
1. Vasoconstriction: The blood vessels in the skin constrict under the influence of posteriorhypothalamic sympathetic centres which reduce the blood flow to the skin.
2. Piloerection: Piloerection means hairs “standing on end”. Sympathetic stimulation causes
the arrector pili muscles attached to the hair follicles to contract, which brings the hairs to
an upright stance. The upright projection of the hairs allows them to entrap a thick layer
of air next to the skin which acts as insulator, so that transfer of heat to the surroundingsis greatly depressed.
3. Increase in heat production (thermogenesis): Endothermic metabolic rates are several
times higher than those of ectotherms. The metabolic heat production of endotherms is
regulated in response to fluctuations in the environment temperature. This phenomenon
is known as adaptive thermogenesis or facultative thermogenesis. It can be defined as
“Heat production by metabolic processes in response to environmental temperature with the purpose
of protecting the organism from cold exposure and buffering body temperature from environmental
temperature fluctuations”. Under cold temperature stress, heat production by the metabolic
activities increased tremendously by promoting shivering, sympathetic excitation of heat
production, and thyroxine secretion. These mechanisms will be discussed later. Extremeshivering can increase the temperature four to five times the normal production.
13.3.2 Ectotherms’ Response to Temperature Changes
Ectotherms cannot maintain stable body temperature and their body temperature relies on the
external temperature. They depend more on energy assimilation rather than utilizing it for
temperature regulation. Therefore, ectotherms regulate their body temperature behaviourally
and by cardiovascular modulation of heating and cooling rates. At the same time, metabolism
and other essential rate functions are regulated so that reaction rates remain relatively constant
even when body temperatures vary. This process is known as acclimatization or temperature
compensation. For example, many fish adjust metabolic capacities to compensate for seasonal
variation in water temperature with the result that metabolic performance remains relatively
stable throughout the year. Reptiles often regulate their body temperature to different levels
in different seasons to minimize the behavioural cost of thermoregulation. At the same time,
tissue metabolic capacities are adjusted to counteract thermodynamically-induced changes inrate functions.
Response to Hot Temperature
When the external temperature increases, ectotherms protect their bodies from overheatingusing various mechanisms. These are:
1. Use of microhabitat: Under extreme heat conditions, many ectotherms like lizards and
snakes prefer to stay in shade, either beneath the rocks, crevices or underground burrows.Amphibians and fishes enter cold water when their body temperature increases.
2. Acclimatization: If a salamander living at 10°C is exposed to 20°C, its metabolic rate
increases rapidly. But if the exposure to the higher temperature lasts for several days,
the animal experiences a compensating decrease in the metabolic rate. This decrease
in the metabolic rate is due to acclimatization. The higher metabolic rate is due to the
increase in the enzymes activity with temperature. However, with prolonged exposure to
the condition, the metabolic rates decrease to prevent excessive energy loss. Ectotherms
also exhibit acclimatization of temperature tolerance range with animal acclimated to
high temperature are able to tolerate higher temperature than those exposed only to low
temperature. Similarly, cold acclimated animals have better tolerance to low temperaturethan high temperature acclimated animal.
Response to Cold Temperature
Ectotherms response to cold temperature is exactly opposite to the response shown whenexposed to hot temperature. That is:
1. Basking to sun: When the body temperature of the ectotherms becomes colder than the
normal, the animals either bask to sunlight to warm up the body or move to a warmer
place. Under extreme cold conditions, all the metabolic activities may cease and theanimals enter the state of torpor (reduced metabolic activities).
2. Cold Acclimatization: Decrease in the temperature result in reduced metabolic rate.
Therefore as a compensatory measures to meet the require body metabolism, the cold
acclimatization of ectotherms is characterized by increase in concentration of various
metabolic enzymes. There is also significant increase in the mitochondria and capillaries
concentration in the skeletal muscle. This increase the ATP production through aerobic
respiration in these tissues. Therefore, in those animals which have prolonged exposure
to cold temperature, there may be increase in the locomotion, though the basal rates ofmetabolism remain below the warm acclimatized animals.
13.4 THE ROLE OF THE BRAIN: HYPOTHALAMUS ANDTHERMORECEPTORS IN TEMPERATURE REGULATION
ACTIVITY 4
Study the role of hypothalamus and different thermoreceptors in thermoregulation.
Make a PowerPoint presentation and present it in front of the class. Discuss yourpresentation with your teacher and seek suggestions for any improvements.
So far we have discussed that on the basis of types of thermoregulation, all the living organisms
can be classified into two groups – ectotherms and endotherms. Endotherms can regulate their
body temperature within a narrow range through various physiological mechanisms while
ectotherms being depended on external temperature mostly rely on their behaviour to maintain
body temperature. But how do these animals sense and counter the changing temperature oftheir body will be discussed in the section.
13.4.1 Thermoreceptors
A thermoreceptor is a sensory receptor which is basically the receptive portion of a sensory neuron
that converts the absolute and relative changes in temperature, primarily within the innocuous range
to nerves impulses. Thermoreception is the sense by which an organism perceives the temperature
of the external and internal environment from the information supply by thermoreceptors.
In vertebrates, most of the thermoreceptors are found in skins which are actually free nerve
endings. Deep body thermoreceptors are also found mainly in the spinal cord, in the abdominal
viscera, and in or around the great veins in the upper abdomen and thorax region.
Mammals have at least two types of thermoreceptors – the warm receptors, those that detect
heat or temperatures above normal body temperature and cold receptors, those that detect
cold or temperatures below body temperature. The warm receptors are generally unmyelinated
nerves fibres, while cold receptors have thinly myelinated axons and hence faster conduction
velocity. Incerasing body temperature results in an increase in the action potential discharge rate
of warm receptors while cooling results in decrease. On the other hand, cold receptors’ firing
rate increases during cooling and decreases during warming. Another types of receptor called
nociceptors, detect pain due to extreme cold or heat which is beyond certain threshold limits.
A specialized form of thermoception known as distance thermoreception is found in some
snakes like pit viper and boa, use a specialized type of thermoreceptor which can sense the
infrared radiation emitted by hot objects. The snake’s face has a pair of holes, or pits, lined
with temperature sensors. These sensors indirectly detect infrared radiation by its heating effect
on the skin inside the pit which helps them to locate their warm blooded prey. The commonvampire bat may also have specialized infrared sensors on its nose.
13.4.2 Hypothalamus
The hypothalamus is a very small, but extremely important part of the brain that acts as the link
between the endocrine and nervous systems of the body. The hypothalamus plays a significant
role in the endocrine system and is responsible for maintaining the body’s homeostasis by
stimulating or inhibiting many key processes, including heartbeat rate and blood pressure,
body temperature, fluid and electrolyte balance, appetite and body weight, glandular secretions
of the stomach and intestines, production of substances that influence the pituitary gland torelease hormones and sleep cycles.
13.4.3 Thermoregulation—Role of Hypothalamus
Thermoregulation is carried out almost entirely by nervous feedback mechanisms, and
almost all these operate through temperature-regulating centres located in the hypothalamus
(Figure 13.4). The hypothalamus contains large numbers of heat-sensitive as well as coldsensitive
neurons which acts as thermoreceptor, sensing the temperature of the brain. The
posterior hypothalamus region contain the thermoregulatory centre which integrate the signals
from of all the thermoreceptors found in skin, deep organs and skeletal muscles, as well as
from the anterior hypothalamus and control the heat-producing and heat-conserving reactionsof the body.
Cooling Mechanism
When the body temperature increases beyond the set-point, the anterior hypothalamus is
heated. The posterior hypothalamus senses the heat and inhibits the adrenergic activity of the
sympathetic nervous system, which control vasoconstriction and metabolic rate. This causes
cutaneous vasodilation and increase heat loss through skin. It also reduces the body metabolic
rate resulting in decreasing heat production through metabolic reactions. Under intense heating,
the cholinergic sympathetic fibres innervating the sweat glands release acetylcholine, stimulating
the secretion of sweat. Many behavioural responses to heat, such as lethargy, resting in shade,lying down with limbs spread out, etc., decreases heat production and increases heat loss.
Heating Mechanism
When the body temperature falls below the set-point, the body regulating mechanism tries to
reduce heat loss and increase heat production. The immediate response to cold is vasoconstriction
throughout the skin. The result is vasoconstriction of the skin blood vessels, reducing the blood
flow and subsequent heat loss through skin. Sympathetic stimulation also causes piloerectionand reduces the heat loss from the body by trapping heat within the body hair.
The primary motor centre for shivering is excited by the cold signals from skin and spinal cord
which cause shivering of the skeletal muscles. Intense shivering can increase the body heat
production four to five times normal. Cooling the anterior hypothalamic due to decrease in body
temperature stimulates hypothalamus to increases the production of the neurosecretory hormone
thyrotropin-releasing hormone. This hormone in turn stimulates the anterior pituitary gland,
to secrete thyroid-stimulating hormone. Thyroid-stimulating hormone then stimulates thyroid
glands to increased output of thyroxine. The increased thyroxine level in the blood increasesthe rate of cellular metabolism throughout the body and hence increases heat production.
Figure 13.4: Neural feedback mechanism for regulation of body temperature
13.5 EFFECT OF TEMPERATURE CONDITIONS ON ANIMAL BEHAVIOUR
ACTIVITY 5
Aim: To investigate the effect of temperature conditions on animal behaviour.
Materials Required:
1. A long piece of metal at least 1 cm thick
2. Hot plates
3. Ice
4. Crickets/Cockroach
5. Transparent plastic pipe (at least 6 cm in diameter).
Procedure:
1. Cut the transparent plastic pipe longitudinally into two equal halves.
2. Place one end of the metal rod on a hot plate and the other end in ice to form a
continuous thermal gradient.
3. Over top the metal rod, place the long half cylinder clear plastic pipe and seal the ends with
cotton.
4. Release some 5–10 crickets/cockroachcs into the tunnel.
5. Observe the behaviour of the animals inside the tunnels.
6. Remove the hot plates and ice from the ends of the metal rods.
7. Observe the change in the behaviour of the animals.
Discussion:
1. Observe whether the animals seek out a preferred temperature or do they remain
dispersed.
2. Note down the temperature of the point of the tunnels where the animals aggregate.3. Discuss your result in the class.
Temperature generally influences the behavioural pattern of animals. In temperate waters, the
influence of temperature on the behaviour of wood borers is profound. For example, in the winter
months in general, both Martesia and Teredo occur in smaller numbers in comparison with Bankia
campanulaia whose intensity of attack is highest during the winter months. Further, the advantage
gained by certain cold blooded animals through thermotaxis or orientation towards a source of
heat are quite interesting. Ticks locate their warm blood hosts by a turning reaction to the heat
of their bodies. Certain snakes such as rattle snake, copper heads, and pit vipers are able to detectmammals and birds by their body heat which remains slightly warmer than the surroundings.
Even in the dark, these snakes strike on their prey with an unnerving accuracy, due to heat
radiation coming from the prey. The arrival of cold weather in temperate zones causes thesnakes to coil up and huddle together.
However, changes in temperature conditions affect the normal adaptational behaviour of
animals. For example, animal species that hibernate throughout winters end their hibernation
sooner than normal due to intense climatic changes. This disruption from normal hibernation
could mean life or death for these species. Migration patterns of many animal species have
also been affected due to temperature change. One of the reasons for change in migration
patterns is loss of habitat at either end of the migratory route. Another reason for change is
that some animals are travelling farther towards higher altitudes in search of colder climates,
invading the territory of already established species. Many animals cover long distances to
reach warmer climates for breeding purposes. However, the devastation of migratory route
or loss of habitat has forced these species to either change or not migrate at all. The same ishappening for aquatic animals.
13.6 TEMPERATURE CONTROLS IN PLANTS
ACTIVITY 6
Select a plant grown in extreme cold and hot environments.
Study the plant grown in hot climate and the plant grown in cold climate.
Point out various adaptive features of the plants.Make a PowerPoint presentation and present it in the class.
Like all the other living organisms, plants depend on enzymes catalyzed chemical reactions for
their growth and development. For example, plants synthesize their own food from water and
carbon dioxide using sunlight through photosynthesis. The process of photosynthesis involves
a series of complex enzyme system and other proteins. Therefore, along with carbon dioxide,
water, light, nutrients and humidity, temperature is also one of the limiting factors for growth
and development of plants.
Unlike animals, plants remain fixed in a particular site and absorb heat from the sunlight. The
excess heat from the body is released to the surrounding through radiation and evaporation.
The process of evaporation of water from the leaves and stem of plants to the surrounding
environment is known as transpiration. It occurs through stomata, small opening located on
the underside of the leaves. The stomata are specialized cells in the leaves which can open or
close, limiting the amount of water vapour that can evaporate. Higher temperature causes the
opening of stomata whereas colder temperature causes the opening to close. The opening of
the stomata and hence the transpiration rate of plants depends on environmental conditions
such as light, temperature, the level of atmospheric CO2 and relative humidity. Higher relative
humidity leads to more opening, while higher CO2 levels lead to closing of stomata. Under
high environmental temperature, the plant body gets heat up. In order to cool down, the plant
increases its transpiration rate. The evaporative loss of water from the plant’s body lowers thetemperature.
Besides transpiration, many plants have different adaptations that help them survive in extreme
temperature conditions ranging from hot and arid deserts to cold and snow covered mountains.
These adaptations make it difficult for the plant to survive in a different place other than the
one they are adapted to. This explains why certain plants are found in one area, but not in
another. For example, cactus plants, adapted to desert conditions can’t survive in the Arctic.These adaptations will be discussed later in this unit.
13.6.1 Effect of Temperature Changes on Plants
The most obvious effect of temperature on plants is changes in the rate of photosynthesis
and respiration. Both processes increase with rise in the temperature upto a certain limits.
However, increase in temperature beyond the limits, the rate of respiration exceeds the rate ofphotosynthesis and the plants productivity decreases.
Another important effect of temperature is during the process of germination of seeds. Like
most other processes it also depends on various factors including air, water, light, and, of course,
temperature. In many plant species, germination is triggered by either a high or low temperature
period that destroys germination inhibitors. This allows the plant to measure the end of winter
season for spring germination or end of summer for fall germination. For example, winter
adapted plant seeds remain dormant until they experience cooler temperatures. Temperature of
4°C is cool enough to end dormancy for most cool dormant seeds, but some groups, especially
within the family Ranunculaceae and others, need conditions cooler than –5°C. On the other
hand, some plants like Fire poppy (
) seeds will only germinate after hot
temperatures during a forest fire which cracks their seed coats. The fire does not cause direct
germination, rather weakens the seed coat to allow hydration of the embryo.
Pollination is another phenological stage of plants sensitive to temperature extremes across
all species. Since pollination is carried out by pollinators like honey bees, butterflies etc., anyfactors including temperature that affect these pollinators will certainly affect the process.
Heat Adapted Plants
In extremely hot and dry desert region with annual rainfall averages less than 10 inches per year,
and there is a lot of direct sunlight shining on the plants, the main strategy for the survival of
the plants is to avoid extensive water loss through transpiration. Therefore, in such region many
plants called succulents, like cactus can store water in their stems or leaves. Some plants are
leafless or have small seasonal leaves that only grow after rains. These leafless plants conduct
photosynthesis in their green stems. Leaves are often modified into spines to discourage animals
from eating plants for water. Also waxy coating on stems and leaves help reduce water loss.
Other plants have very long root systems that spread out wide or go deep into the ground toabsorb water.
On the other hand, in hot and humid tropical rainforest, the abundance of water can cause
problems such as promoting the growth of bacteria and fungi which could be harmful to
plants. Heavy rainfall also increases the risk of flooding, soil erosion, and rapid leaching of
nutrients from the soil. Plants grow rapidly and quickly use up any organic material left from
decomposing plants and animals. The tropical rainforest is very thick, and not much sunlight
is able to penetrate to the forest floor. However, the plants at the top of the rainforest in the
canopy must be able to survive the intense sunlight. Therefore, the plants in the tropical rainforest
usually have large leaves with drip tips and waxy surfaces allow water to run off easily. Someplants grow on other plants to reach the sunlight.
Similarly, in aquatic plants adapted for life in water, the leaves are very large, fleshy and waxy
coated. Increase surface area allows plants to lose excess water while the shiny wax coating
discourages the growth of microbes. The roots and stems are highly reduced since water,nutrients, and dissolved gases are absorbed from the water directly through the leaves.
Cold Adapted Plants
In extremely cold region like tundra which is characterized by a permanently frozen sub-layer of
soil called permafrost, the drainage is poor and evaporation slow. With the region receiving very
little precipitation, about 4 to 10 inches per year usually in the form of snow or ice, plant life is
dominated by small, low growing mosses, grasses, and sedges. Plants are darker in colour, some
even red which helps them absorb solar heat. Some plants are covered with hair which helpskeep them warm while others grow in clumps to protect one another from the wind and cold.
In a slightly warmer temperate forest, with temperature varies from hot in the summer to
below freezing point in the winter, many trees are deciduous that is they drop their leaves in
the autumn to avoid cold winter, and grow new ones in spring. These trees have thin, broad,
light-weight leaves that can capture a lot of sunlight to make a lot of food during the warm
weather and when the weather gets cooler, the broad leaves cause too much water loss and can
be weighed down by too much snow, so the tree drops its leaves. They usually have thick barkto protect against cold winters.
APPLICATION 13.2
1.Complete with appropriate terms:
(i) Piloerection helps in ........................ .
(ii) ........................ can regulate their body within a narrow range.
(iii) ........................ receptors detect pain due to extreme cold or heat.
(iv) ........................ is responsible for maintaining homeostasis.
(v) Plants in tropical forests have ........................, and ........................ .(vi) Plants in cold regions shed their leaves to ........................ .
2.a) Describe the immediate environment of a typical cell within the body of a mammal.
b) Explain why it is important that the internal environment of a mammal is carefully regulated.
c) Explain how the following are involved in maintaining the internal environment: stimuli,
receptors, central control, coordination systems and effectors.
d)Explain the meaning of the terms homeostasis and negative feedback.
e) Distinguish between the input and the output in a homeostatic control mechanism3.The diagram shows the way in which temperature is regulated in body of a mammal
a) Which part of the brain is represented by box X?
b) i. How does the heat loss center control the effectors which lower the body temperature?ii. Explain how blood vessels can act as effectors and lower the body temperature?
13.7 SUMMARY
• Endotherms or warm-blooded animals are those animals that actively maintain a stable
body temperature by generating heat.
• Ectotherms or cold-blooded animals are those animals whose body temperature depends
on their surrounding environment.
• Ectotherms can conserve more energy while endotherms use their energy to maintain
body temperature, hence remain active even in wide temperature changes.
• All the enzymes have an optimum range of temperature beyond which they cease to function.
• Temperature is one of the most important factors which directly or indirectly influence
the distribution of organisms to a large extend.
• Temperature above or below the limits of tolerance can have various effects on animal’s
body including cells, metabolism, reproduction etc.
• Bergmann’s rule states that animals living in the colder climates tend to be larger than
those living in warmer climates.
• According to Allen’s rule, animals living in the colder climates have more rounded and
compact form which is achieved by reducing the size of the body extremities i.e., ears,
limbs, tails etc.
• The counter current heat exchanger is generally located in body extremities like limbs,
neck, gills, which are directly in contact to the external environment and helps to conserve
or loss body heat.
• Desert dwelling mammals and birds have specialized kidneys with long loops of Henle
compared to animals that live in aquatic environments and less arid regions.
• Hibernation is the state of dormancy during the cold conditions, i.e., winter.
• Aestivation or summer dormancy is a state of animal dormancy, characterized by inactivity
and a lowered metabolic rate, in response to high temperatures and arid conditions.
• Torpor is the state of decreased physiological activity in an animal, usually by a reduced
body temperature and metabolic rate.
• Thermogenesis or mechanisms of heat production, such as shivering and chemical
thermogenesis, are strongly inhibited when exposed to hot temperature.
• Ectotherms depends more on their behaviour to regulate their body temperature.
• Ectoderms can adjust metabolism and other essential rate functions so that reaction rates
remain relatively constant even when body temperatures vary. This process is known as
acclimatization or temperature compensation.
• A thermoreceptor is a sensory receptor which is basically the receptive portion of a sensory
neuron that converts the absolute and relative changes in temperature to nerves impulses.
• The hypothalamus is a small, but extremely important part of the brain that acts as the
link between the endocrine and nervous systems of the body.
• The primary motor centre for shivering is excited by the cold signals from skin and spinal
cord and depress by heat.
• All animals have a preferred range of temperature conditions at which it functions most
optimally.
• Changes in temperature conditions affect the normal behavioural adaptations of the
animals.
• Plants also depends on enzymes catalyzed chemical reactions for their growth and
development.
• The process of evaporation of water from the leaves and stem of plants to the
surrounding environment is known as transpiration.
• The stomata are specialized cells in the leaves which can open or close, limiting the
amount of water vapour that can evaporate.
• Temperature affects the photosynthesis, respiration, germination as well as pollination
of plants.
• Plants adapted to hot and dry climate have reduced leaves and longer roots.
• The large waxy coated leaves of plants in tropical rainforest are waterproof and help in
losing water more easily.
• Small, low growing mosses, grasses, and sedges are the characteristics of extremely coldregion like tundra.
13.8 GLOSSARY
• Adaptive thermogenesis: Heat production by metabolic processes in response to
environmental temperature.
• Aestivation: State of animal dormancy, characterized by inactivity and a lowered
metabolic rate, in response to high temperatures and arid conditions.
• Hibernation: State of dormancy during the cold conditions, i.e., winter.
• Hyperthermia: Condition when the body temperature is higher than normal.
• Hypothermia: Condition of low body temperature.
• Torpor: State of decreased physiological activity in an animal, usually by a reduced body
temperature and metabolic rate.
• Transpiration: The process of evaporation of water from the leaves and stem of plantsto the surrounding environment.
END UNIT ASSESSMENT 13
I. State whether the following statements are True (T) or False (F)
1. All the living organisms have a particular range of temperature within which they
can best survive and reproduce.
2. Nocturnality is the simplest form of behavioural adaptation characterized by activity
during the day and sleeping during the night.
3. Crepuscular animals take advantage of the slightly cooler mornings and evenings to
escape the daytime heat, and to evaporate less water.
4. Body temperature of Ectotherms rely on the external temperature.
5. Thermoregulation in endotherms depends on food and water availability.
6. Invertebrates, most of the thermo receptors are found in skins.
7. Changes in temperature conditions do not affect the normal adaptation behaviour
of animals.
8. Hibernation is the state of dormancy during the cold conditions, i.e., winter.
9. Most of the heat in our body is generated through metabolic activity.10. Larger animals can easily lose their body heat to their surrounding environment.
II. Multiple Choice Questions
1. The physical movement of animals over a long distance from one area to another is
known as ........................... .
(a) Hibernation (b) Aestivation
(c) Migration (d) None of these
2. Large animals like lions prefer to hunt at night to ........................... .
(a) conserve water (b) avoid direct exposure to heat
(c) utilise less energy (d) All of these
3. With rise in the temperature, the plant’s rate of .......................... increases.
(a) respiration (b) photosynthesis
(c) both (a) and (b) (d) None of these
4. Temperature of .......................... depends on the temperature of external environments.
(a) Ectotherms (b) Endotherms
(c) Both (a) and (b) (d) None of these
5. The state of reduced metabolic rate on a daily basis is an example of
(a) Hibernation (b) Aestivation
(c) Torpor (d) None of the above
6. Reptiles are
(a) Ectotherms (b) Endotherms
(c) Homeotherms (d) Heterotherms
7. Animals living in warmer climates have longer ears according to
(a) Bergmann’s Rule (b) Allen’s Rule
(c) Gloger’s rule (d) Jordon’s rule
8. The process of increasing body temperature in response to the environmental
temperature is known as
(a) Acclimatization (b) Adaptive thermogenesis
(c) Piloerection (d) Insulation
9. The waxy coating of leaves of aquatic plants helps to
(a) Conserve water (b) Increase transpiration rate
(c) Avoid growth of microbes (d) Float in water
10. The rate of transpiration of plants depends on environmental conditions such as
(a) Temperature (b) Level of atmospheric CO2
(c) Relative humidity (d) All the above
11. Increased thyroxin level in our blood increase the rate of
(a) Metabolism (b) Excretion(c) Muscle contraction (d) Food assimilation
III. Long Answer Type Questions
1. In your own words, explain the importance of temperature regulation.
2. Describe the morphological, physiological and behavioural adaptations to temperature
changes in the environment.
3. Giving suitable examples, describe the responses to cold and hot conditions by
endothermic and ectothermic animals.
4. Explain the role of the brain and thermo receptors in temperature regulation.
5. Describe the different processes in which plants minimise overheating.
6. In your own words, explain the importance of maintaining fairly constant temperatures
for efficient metabolism.
7. List few adaptive features shown by plants inhabiting extreme cold and hot
environments.
8. Why is thermoregulation assessed with health and disorder? How is thermoregulationcorrelated to the environment? What changes can help organism’s survival?