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water availability for organisms is determined by movement of water down its concentration gradient
- concentration gradients influence the movement of water between an organism and its enviroment
- the tendency of water to move down concentration gradients and the magnitude of those gradients from organism to its enviroment determine whether an organism tends to lose or gain water from the enviroment.
Evaporation accounts for most water losses in terrestial animals
On land, evaporation also accounts for much of the water lost by organisms. The potential for such evaporative water loss depends upon the temperature and water content of the air around the organism.
When does evaporative cooling work best? (VPD)
As the amount of water vapor in the surrounding air increases, the water concentration gradient from organism tot he air is reduced and the rate at at which oragnism loses water to the atmosphere decreases. This is the reason the evapoative air coolers work poorly in humid climates, where the water content of the air is high. These mechanical systems work best in arid climates where there is a steep gradient of water concentration from evporative cooler to the air. A steep water concentration gradient is conductive to a high rate of evaporation.
What is diffusion?
-trasport of material due to random movement of particles: net movement is from areas of high concentration to areas of low concentration.
What is hyperosmotic, hypoosmotic and iosomotic ?
- a term describing organisms with which body fluids witha lower concentration of water and a higher solute concentration than the external enviroment.
- a term describing organisms with body fluids with higher concentration of water and lower sloute concentration than the external eviroment.
- a term describing organisms with body fluida containing the same concentration of water and solutes as the external environment
What is omosis?
-diffusion of water down its concentration gradient
Hperosomtic fish in fresh water, hypoosomtic fish in saltwater, isosmotic seastar in saltwater (know how they maintain their ionic and hydric balance steady = homeostatsis)
Water potential and how does water move through a plant? What is the Psi of pure water = and Psi of dry air =?
- the capaticy of water to do work, which is determined by its free enegery content: water flow from posotions of higher to lower free energy. Increasing solute concentration decrease water pontential.
Psi of pure water =0
Psi of dry air = -100
What makes water to be transported by the phloem in a plant?
How do calucate the Psi of a plant?
- Ψ=ΨsolutesΨsolutes is the reduction in water potenital due to dissolved substances which is anegative number.
Ψplant = Ψsolute + Ψmatric + Ψpressure : know what the different terms mean
- Ψmatric is the reduction in the water potential dueto matric fostance forces with in the plant
- Ψpressure is the reduction in water pontential due to negative pressure created by water evaporating from leaves
- Ψsolute is the reducetion in water potential due to dissolved substances , which is a negative number
What are matic forces?
- a force resulting from water's tendency to adhere to the walls of containers such as cell walls or the soil particles lining a soil pore.
what is the equation for water regulation in animals ?
•Wia= Wd + Wf + Wa - We - Ws
- •Wia= Animal’s internal water
- •Wd = Drinking
- •Wf = Food
- •Wa = Absorbed by air
- •We = Evaporation
- •Ws = Secretion / Excretion
What is the eqution for water regultion in plants?
•Wip= Wr + Wa - Wt - Ws
- •Wip= Plant’s internal water
- •Wr =Roots
- •Wa = absorption
- •Wt = (evapo)Transpiration
- •Ws = Secretions
What is metabolic water?
- water released within an organism during the process of cellular respriation
- •Most terrestrial animals satisfy their water needs via eating and drinking.
- Can also be gained via metabolism through oxidation of glucose:
- C6H12O6 + 6O2 à 6CO2 + 6H2O
root to shoot ratio in a dry vs. well watered plant
- The extent of root development by plants often relects differences in water availability.
- Studies of root systems in different cliamtes show how plants in dry climates gorw more roots than do plants in moist climates.
- In dry climates, plants roots tend to grow deeper in the soil ansd to constitute a greater proportion of plant biomass.
Analogies to conserve water between a camel and a cacuts
- conserves body water by reducing rate of heat gain
- faces into the sun, reducing the body surface it exposes to direct sunlight
- its thick hair insulates it from intense desert sun and rather than sweating sufficiently to keep body temperature down, the camel allows its body temperature to rise up by to 7o C. This reduces the temperature difference betweenthe camel and the environment and so decreases the rate of additional heating.
- Recucde heating translates into reduced water loss by evaporation.
- The trunk and arms of the plant act as organs in which the cactus can store large quantites of water. During droughts, it draws on these stored reserves and so can endure lange periods without water
- Has large network of roots with wich it intake large amount of water
- it keeps its stoma closed during the day when transpiration losses would be that highest
- In the absenceof transpriation, in the full sun, the internal temperature of the cactus rises to over 50o C. the higher body temperature can be an advantage beacues it reduces the rate of additional heating.
- The rate of heating is also reduced by the shape and oreintaion of it trunk and arms . At midday, when the potential for heating is the greatest, it exposes mainly the tips of its arms ans trunk to diredt sun. In addition the tips are the arms and trunk are insulated by a layer of plant hairs and a thick tangle of spines which relfect sunlight ans shade the growing tips of the cactus.
Differences between a scorpion ans a cicada in a hot environment
- approach is to slow down, conserve and stay out of the sun
- as slow metablism means that they can subsist on low rations of food and little water durong resiration.
conserves water by spending moxt of their time in their burrows where the humidity is higher than the surface they only come out at night to eat and mate when is cooler.
they are well waterproofed; hydrocarbons in thier cuticles seal in moister.
cable of evaporative cooling (sweat)
the tap into a rich supply of water
they feed on plant fluids. its scope for water acquisition is extended up to 30m deep into the soil by tap roots of the mesquite host plant.
it is able to sustain high rates of water loss through evaporation. high we
, because it is able to balance these losses with a high rate of water acquisition, high wd.
Water regulation in fishes whether they are isotonic, hypertonic or hypotonic
Marine and freshwater organisms use complementary mechanism for water and salt regulation.
Wi=Wd - Ws ± Wo
- Wi= Internal water
- Wd= drinking
- Ws= excreting
- Wo= osmosis
an aquatic organism may either gain or lose water depending on the organism and the ebviroment.
How does an isotonic/ hyperotic or hypotonic fish regulate its water balance (=maintain homeostatsis)?
Then isosmtic animal does n have to expend energy, overcoming an osmotic gradient. this startegy is not witho costs, however. thought the total concentration of solutes is the same inside and outside the animal, there are differences in the concentrations of some individual solutes.these concentration differentials can only be determined by active transport, which comsumes some energy
as a consequence of being slightly hyperosmotic, sharks slowly gain water though osmosis, that is Wo
is slightly paotive . the water that diffusee into the shark mainly across the gills, is pumped out by the kidneys and exits as urine. soduim, because it is maintained at approximately 2/3 its concentration n salt water, diffuses into the shark from seawater across the gill memebranes and some soduim enter with food. sharks excrete excess soduim maily through a specialized gland associated with the rectum called the salt gland. the main point here is that the sharks and thier relavites reduce the costof osmoregulation, regulation of internal salt and water concentration, by decreasing the osomtic gradient between themselves and the external enviroment.
sharks and marine bony have body fluids that are stongly hypoosmotic to the surronding medium. as a consequence, they lose water to the surrouding sea water, mostly across their gills. marine bony fish make uo these water losses by drinking seawater. however drinking icreases salt gain. the fish rid themselves if excess salts in 2 ways. specialized "chloride" cells at the base of their gills secrect soduim ans chloride directly to the surrounding seawater , while the kidneys excrete magnesium and sulfate. howere the loss of water through the kidnesys is low because the volume of urine is low.
freshwater fish are hyperosomtic: they have body fluids that contain more salt and less water than the surrounding medium. as a conqunece, water floods inward and salt diffuse outward across their gills. fressh water fish excrete water as large quantities of dulite urine. they replace the salts they lose to the external environement in 2 ways. chloride cells at teh base of the gill flaments absorbs sodium and chloride from the water, while other salts are ingested with food.