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

• 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.

Great Basincold

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?

Waterout;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?

C3Problem with C3:

Rubisco - higher affinity to O2 than CO2, especiallyat high T (and low H2O)

O2

C4: PS in environment with high water stress hot/dry habitats (especially tropical grasses)

Low O2;High C-gain

High O2