Transcript Lakes and oceans do not freeze solid because the density of water

Lakes and oceans do not freeze solid
because the density of water reaches a
maximum at 4º C.
4º C is temperature in most depths of
lakes
***Why don’t these aquatic organisms sink?
Hot deserts: stress from high T and low
moisture
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Animals: increased tolerance, aestivation, and
behavioral avoidance
Evaporative cooling limited by small body size
and low water availability; larger organisms
have advantage.
Plants: increased tolerance, resistance to
water loss, and timing of life cycle
***How is the kangaroo rat adapted to the
desert? water balance in rats vs. humans
Traits that allow kangaroo rats to live
without drinking water.
• Vary body temperature.
• Control water loss by a turbinal exchange system,
concentrated urine, and dry feces.
• Escape extreme conditions by using burrows and
nocturnal activity.
• Use high carbo food (seeds) which provides metabolic
water.
• Store food in humid burrow which recycles free water.
Water can be the limiting physical factor
for plants too. In some latitudes
accompanied by high T.
cold Great Basin
hot
How do plants acquire water?
Availability of water depends on the
physical structure of soil.
***Which soil has greater surface area?
Which soil holds more water? Which drains
water better? Why?
Plants obtain water from the soil by the
osmotic potential of their root cells.
***What increases osmotic potential?
Summarize the principle that causes water
to flow from soil into root.
Forces generated
by transpiration
help to move water
from roots to
leaves.
Steep H2O gradient;
weak CO2 gradient;
***Summarize principle
governing movement
along gradients.
What is consequence
at leaf level?
Water
out;
CO2 in
Structure and function in arid environments:
***What adaptation minimizes water loss?
***How do dense hairs and spines limit water
loss?
***How do sunken stomates filled with
hairs lessen water loss?
C3
Problem with C3:
O2
Rubisco - higher affinity
to O2 than CO2, especially
at high T (and low H2O)
C4: PS in environment with high water stress
hot/dry habitats (especially tropical grasses)
High O2
Low O2;
High C-gain