Page 343 - Biology_F5

Biology for Advanced Level Secondary Schools

tendency usually takes place during winter the thickness of insulating warm hair to
season, which sometimes is referred to as be reduced, and therefore, the body heat is
winter dormancy. readily dispersed.
Winter dormancy is associated with Maintenance of a constant body
reduced body metabolic rate, low body temperature in cold climates
temperatures, slow breathing and low Endotherms living in cold environment
FOR ONLINE READING ONLY
heartbeat rate. The animal appears to be and those in hot climates experiencing cold
in a deep sleep for several days, weeks weather have the following adaptations
or months depending on the species. which enable them to maintain constant
This helps to conserve energy, especially body temperatures:
during winter when food is scarce.
Before entering into hibernation, most (a) Vasoconstriction
animals eat a large amount of food and When the animal is subjected to cold
store energy in fat deposits to survive the conditions, the superficial arterioles are
winter. Hibernation can also take place constricted. This reduces the quantity of
during the hottest period or summer. blood reaching the skin surface. Much
This state is called aestivation or summer blood passes beneath the insulating layer
dormancy. Some animal species that of subcutaneous fat; therefore, little heat
aestivate include reptiles. The arousal of is lost to the outside.
an animal from hibernation state usually
occurs spontaneously. It is driven by some (b) Shivering
internal mechanisms. External stimuli In cold conditions, the skeletal muscles
often fail to wake the hibernating or of the body may undergo rhythmic
aestivating animal, making it subject to involuntary contractions which increase
predation if it is discovered by its enemies. the amount of heat produced in the body.

(g) Insulation (c) Insulation
This is provided by a layer of fur or fat that It is achieved by an external covering of
protects or blubs the body against changes fur or feathers and or an internal layer
in the environmental temperature. The of subcutaneous fat. Their thickness is
thick coat of fur is called insulator while related to the intensity of coldness to that
environment. It is an effective means of
the thick layer of fat is called blubber. reducing heat loss from the body.
The insulator or blubber layer helps to
retain body heat and keeps the animal’s (d) Increased metabolic rate
body temperature constant. Animals During cold conditions, the liver increases
in the warm climates usually have fur its metabolic rate. There is also increased
with light colours to enhance sun rays’ activity of the adrenal, thyroid, and pituitary
reflection and thereby minimising heat glands resulting into secretion of hormones
gain and accelerating heat loss from the that help to increase the body metabolic rate;
body. During this process, the hair erector hence, additional heat is produced in the
muscles in the skin are relaxed and the fur body. The increased metabolic rate of the
lies close to the skin surface. This causes

Form Five Student’s Book
336