essential for life. It is required to exchange gases (e.g., oxygen and carbon
dioxide) in respiration, it transports nutrients through the body, it is involved
in most metabolic processes, it dilutes and removes wastes, and it serves as
a coolant. Water is acquired by animals through drinking (free
water), through water in their food (preformed
water), and through water produced as a by-product of metabolizing food
(metabolic water, see respiration).
Water is acquired by plants from the soil using their roots.
lost by plants and animals by three avenues:
leaking through outer surface (skin, exoskeleton, etc.).
loss in urine and feces.
loss during gas exchange (breathing, and don't forget that plants must "breathe"
for photosynthesis and respiration
the ways to reduce water lost by the three avenues are given below. Torpor
reduces water lost by all three avenues also.
in cool/moist microclimate; venture out when relative humidity is high.
relatively impermeable materials on outer surface, such as scales, waxes,
surface area (e.g., small leaves)
surface temperatures of body by shading (hairs/spines, etc.)
urine (e.g., the kangaroo rat is
capable of producing urine twice as concentrated as seawater).
feces (e.g., kangaroo rat droppings are five times drier than lab rat
uric acid rather than urea -- uric acid requires 10x less water than urea
to rid the same amount of waste.
in moist microclimate (e.g., burrow); venture out when relative humidity
nasal water condensation: evaporative cooling
in the nasal passageways cools exhaled air. Because
cooler air holds less water than warmer air, water in the cooled,
exhaled air condenses along the nasal passages. The longer, narrower,
nasal passages found in many desert rodents cools air further and condenses
drought-deciduous, dropping leaves/twigs
when soil dries up.
only a few, small, sunken stomata
on the bottomside of leaves.
hairs/spines to increase shading and decrease wind across stomata.
C4 and CAM photosynthesis