Page 360 - Biology_F5

Regulation (Homeostasis)

Water and food consumption Burrows are another type of microenvironment
Human beings obtain about 60% of the that is used by smaller mammals. In Arizona
water they need from the ingested liquids, burrow temperature of a round-tailed ground
30% from ingested food, and 10% from squirrel was recorded. The air temperature
metabolism. Rodents and camels adapted was 40 °C and the soil surface was 70 °C
to arid conditions obtain approximately but the burrow temperature did not exceed
FOR ONLINE READING ONLY
90% of water from metabolism and 10% 29 °C. Many burrows are at a depth where
from ingested food. evaporative cooling is not needed; it does
not get hot enough in the burrows to require
Excretory adaptations this technique.
The ability to excrete concentrated urine
and dry feaces is an important adaptation Torpor and metabolic rate
to arid conditions. Mammals that are Many mammals such as rodents and
adapted to the desert have very long squirrels enter a period of torpor in
loop of Henle compared to animals that response to severe heat. This is a period
live in less arid regions and in aquatic when metabolism decreases, the heart
environments. A longer loop of Henle beat and respiratory system slow down
allows urine to become very concentrated based on a circadian rhythm. Torpor
due to osmotic gradients in the kidneys. can be considered as a water conserving
Desert rodents produce concentrated urine mechanism because the animal’s body
about five times as that of humans. Longer temperature is lowered and it does not
loop of Henle increases the efficiency of have to rely heavily on evaporation. If
water reabsorption and hence a means for the period of torpor becomes longer, it is

conserving water. called aestivation or summer dormancy.

Behavioural adaptations Aestivation allows an animal to survive
Behavioural adaptations are used to when there are high temperatures and
reduce the amount of heat gained by a scarcity of water and or food. An
animals. Therefore, they reduce the aestivating animal can live longer with
need for evaporative cooling. One basic its energy reserves due to lowered
behavioural adaptation is the timing of metabolism. Moreover, there is a reduced
activity rhythms. Nocturnal animals water loss through lowered breath rates.
are able to regulate their heat load by Metabolic rates are lower during torpor
resting during the day, since night-time and aestivation. Mammals adapted to
temperatures can be 15 °C - 20 °C lower desert climates have lower metabolic
than the daytime. Examples of nocturnal rates in general than similar mammals that
animals include the quoll, bilby, and the live in extreme climates. This reduces the
spinifex hopping mouse. internal heat load as well as the water used
for evaporation.

Form Five Student’s Book
353