Page 342 - Biology_F5

Regulation (Homeostasis)

convection and conduction resulting into lick their front legs and chests, cats lick
an increase in blood flow near to the skin inside of their front paws and spread the
surface. In cold environments, the blood saliva across their ears and face. Rats lick
flow in the body escapes the skin through their testicle, and kangaroos lick their fore
the shunt vessels, resulting into reduction arms and wrists.
in heat loss. Just a small amount of blood (d) Use of body extremities
FOR ONLINE READING ONLY
passes into the skin to keep the tissue When compared to related species from
alive. cold climates, animals in warm climates
usually have large extremities such as
(b) Sweating ears and large bushy tail. They are well
Human beings have the ability to control supplied with blood vessels and they are
body temperature through sweating covered by relatively short hairs, making
because their skins are not covered by them good radiators of heat.
fur or feathers. They have sweat glands
over the whole body that enable them (e) Large surface area to volume ratio
to be more efficient at cooling through Animals with a large surface area to
sweating. The human being can produce volume ratio (relatively small animals)

about 1000 ml of sweat per hour. Animals lose energy (temperature) faster than those
with fur have limited sweat glands, which with smaller surface to volume ratio. To
are confined to areas that do not have fur, compensate for this, small animals such
such as pads of the feet in dogs and cats. as mice feed more frequently compared
Animals with feathers, such as birds lack to large animals like lions. The former
sweat glands. Their skins are covered animals also tend to utilise an energy - rich
by feathers which prevent evaporation diet such as nuts which are rich in lipids.
through the skin (evaporation occurs from (f) Behavioural mechanisms
the surface of their lungs and air sacs). Many desert animals regulate their body

(c) Panting and licking temperature by using different behavioural
In animals with few or no sweat glands mechanisms. For example, some animals,
such as dogs and birds, cooling by such as mice and hedgehogs avoid heat by
evaporation takes place through the mouth sheltering under the rocks or by burrowing
and the nose. Dogs hang out their tongues; in the soil during the drought season.
this may result in an increase of breathing Others, like bat avoid hottest periods by
rate and excessive removal of carbon being nocturnal, a tendency of being active
dioxide from the blood thereby reducing during the night and inactive during the day.
heat from the body. Some animals lick This minimises the rate of body metabolic
their bodies to deposit saliva onto their activities during the day and increases at
body surfaces, which provide similar night. Some animals like rodent, ground
means of evaporative cooling. Licking squirrels and bears hibernate during cold
is common to some animals that do not temperatures. Hibernation is the behavioural
sweat, instead they make use of saliva to state whereby an animal becomes inactive,
cool their bodies. For example, rabbits both during the day and at night. This

Form Five Student’s Book
335