Transcript Lecture 3-Adaptations to physical environments

Adaptations to Terrestrial and Aquatic Environments
•Some adaptations of plants for life on land
•Osmotic adaptations of fish for marine life
•Adaptations of animals to desert environments
•Physical adaptations required for large size
•Biochemical adaptations to extreme environments
•Homeostasis and how is it achieved?
Plants evolved root, vascular systems and stomates to obtain
water and nutrients, and pump them through their bodies
•Microorganisms live in water and
depend on diffusion to feed and
cleanse their cells—limited to a few
mm
•Plants pump water s and transport
nutrients to leaves through their
vascular system
Water vapour diffuses from stomates
Water evaporates from mesophyll cells
Tension pulls water into the leaf veins
•transpiration pull is the main
pump
And up the xylem vessels in the stem
•Evaporation at the leaf ‘sucks’
water up through the plant
And up the root
Water moves into the root—osmosis
and into the xylem
When nutrients or water are scarce plants adapt:
grow more roots and less shoots
water and/or soil nutrients
scarce –more allocation to
root development
Water and soil nutrients plentiful—
larger shoots, more growth
Plants control water loss
•Waxy leaf cuticle
•Stomates on the underside—regulate
evaporation
Spines and hairs help desert plants
deal with heat and drought
•still boundary layer that traps
moisture and reduces evaporation
Oleander has its stomates situated within hairy pits on the leafs
under surface
Plants have difficulty trapping CO2 without losing water
Most plants and algae employ the C3 mode
of CO2 uptake—stomates must remain open
for hours--not very water efficient
RUBISCO has a low affinity for CO2
but the spongy mesophyll allows free air flow—
maximize CO2 capture but high water loss
Many plants adapted to arid conditions eg. grasses use the C4 mechanism
•PEP-carboxylase has
much higher affinity for
CO2 than RUBISCO
•Stomates mostly closed
and mesophyll tightly
packed to reduce air
circulation keeps CO2
levels in the leaf low and
conserves water.
•Photosynthesis can be
highly efficient without
water loss, but only
occurs in the bundle
sheath.
CAM plants are even more water efficient than C4 metabolism
•Stomates open at night
only when transpiration
is low
•OAA is formed and
stored within cell
vacuoles.
Desert plants/succulents
Eg Crassulaceae
CAM means
Crassulacean Acid metabolism
•During the day
stomates close and OAA
is recycled to release
CO2 to the CalvinBenson cycle
•Day and night enzymes
have different T-optima
marine fish also live in ‘dry’ environment
Water and salt
balance is a
critical problem
for fish
Marine fish live in water more concentrated than their body tissues
—tend to lose water and must drink to offset water loss.
Freshwater fish live in a dilute medium –tend to take on water & lose salts through gills
—produce dilute urine and take up salts by active uptake.
Tigriopsis is a tiny copepod crustacean that lives in splash pools
and experiences dramatic fluctuations in salt concentration
It responds to these changes with rapid changes in blood
chemistry and metabolic rate.
Tigriopsis responds to high salt stress by producing large quantities of amino acids that make
its blood more concentrated—requires energy
Sharp increase
in metabolic
rate, as amino
acids are
metabolized
In response to a sudden dilution of their environment, they metabolized the amino acids.
Adaptations for life in hot environments
The scarcity of water in the desert
make evaporative cooling very costly
Reduce activity, or go underground
during the day and be more active at
night when it is cool
Many desert plants orient their leaves
away from direct sunlight, and others
shed their leaves and become dormant
during hot and dry periods.
The kangaroo rat has both physiological and behavioural
adaptations for desert environments
Large animals have evolved muscular pumps to circulate
fluids and nutrients around their bodies
CO2 released
into lung and
exhaled
CO2 carried
away in blood
Hemoglobin
in RBC binds
O2
O2 released to
tissues
Insects pump O2 to their body tissues using a tracheal system
The tracheal system
opens to the outside
through spiracles
Trachea divide into
tracheoles which divide into
finer air capillaries
Gas exchange and ion exchange occurs across the surface of
the gills in fishes and other aquatic animals
Filaments and folds
increase surface area
O2 rich water
O2 diffuses
from water
into blood
Blood flow
is counter
current to
water flow
Counter-currents can also be useful for retention—eg heat
Arrows indicate
direction of
heat transfer
Heat is shunted directly from artery to vein in the leg bypassing the foot
and allowing its temperature to drop to conserve body heat
Halophilic bacteria can adapt to high salt concentrations by
producing enzymes with high salinity optima.
Comparison of salinity optima for respiratory enzymes in a
halophilic and halophobic bacteria
Acetylcholinesterase Isozymes in rainbow trout
Winter adapted
trout, T-opt is 2C
Summer adapted
trout, T-opt is 17C
Temperature adaptation in cold-blooded animals often
involves changing enzymes as temperature changes
Homeostasis/regulation often occurs through negative feedback systems
A thermostat
is a typical
negative
feedback
system
What do
we mean
by the term
positive
feedback?
Negative feedback—if T is too high heater switched off, if too low heater switched on. The
feedback is considered negative because the response is opposite to the deviation.
Maintaining a constant internal temperature warmer than the external
environment is costly—the bigger the gradient the bigger the cost
This West-Indian
hummingbird, conserves
metabolic energy by
setting its thermostat
down at night
Set-point 40C
Set-point 20C