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32 terms

Section 9: Excretion and Osmoregulation

biology 1002 memorial university
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Excretion
removal of nitrogenous wastes (containing N), principally breakdown products of proteins (amino acids) + nucleic acids (nitrogenous bases A,G,C,T,U), Nitrogenous waste may be ammonia, urea, uric acid
Osmoregulation
process of regulating salt and water balance in the body
Relationship between excretion and osmoregulation
Products of excretion are removed with water (flushed out), The amount of water required to flush out nitrogenous waste (excretory) products has a significant impact on osmoregulation
Basic Fact of osmoregulation/excretion
In the face of a variety of environmental challenges, it is a fact that over time, in order to survive, the rate of water uptake and water loss in an animal MUST BALANCE
physiological systems of animals
enzymes, cell membranes, tissue systems, function in an internal fluid environment that has a different composition to exterior,Internal conditions must be maintained for optimal functioning
Fresh Water environment
Hypotonic to body fluids, the main problem is osmosis, there is a constant battle against uncontrolled influx of water. Adaptations are required to reduce H2O uptake, or get rid of excess water: To conserve internal solutes (salts) which will tend to diffuse out and to absorb salts from surroundings to replace those that are lost
Deserts or Oceans
Problem - Dehydration (evaporative loss) or OSMOSTIC water loss in a hypertonic environment. Need adaptations for water conservation, plus, in the ocean, excess salts taken in while drinking must also be removed
Osmolarity
Total solute concentration in moles of solute / litre of solution, In biological solutions - osmolarity is measured in milliOsmoles/L (mOsm/L)
OSMOTIC PRESSURE
(of solutions) can be compared by measuring the OSMOLARITY of each solution
Direction of osmosis
From solution with fewer salts in solution, lower osmotic pressure (hypoosmotic), To solution with more salts in solution, greater osmotic pressure (hyperosmotic)
iso-osmotic
Solutions with the same osmolarity, no net water movement
hyperosmotic
solution with more salts in solution, greater osmotic pressure
hypoosmotic
solution with fewer salts in solution, lower osmotic pressure
Ammonia
Very toxic, very soluble, diffuses readily across membranes, cheap to produce. Animals that Excrete Ammonia: Fish - ammonia diffuses as NH4 and is washed away by watery environment
Freshwater fish excretion
gill membrane system actively exchanges NH4, replenishes Na+ that keeps diffusing out while getting rid of toxic NH4,NH4 can be excreted across body surface - continuous release of ammonium ions, especially in aquatic invertebrates
UREA
100,000 times LESS toxic than ammonia, can be transported and stored at high concentrations and excreted in more concentrated forms, And save precious water for homeostasis of body fluids
Uric Acid
for animal that really need to conserve water, relatively non-toxic, relatively insoluble, can be excreted in semi-solid paste form. The best option if water conservation (insects, land snails, many reptiles), or water conservation AND lightness (birds) are issues
How to excrete a solid
Uric acid is formed in the kidneys - still in solution, Transported in solution to cloaca where it joins with ions to form a precipitate, Water is reclaimed and Uric acid is excreted as a white "sludge" along with feces (normal colour)
Hydra (nitrogenous waste)
ammonia, released from cells of epidermis and gastrodermis into water or GVC
Earthworm (nitrogenous waste)
produces urea in urine, terrestrial - lives in moist environments so water is only a concern, not a problem
Grasshopper (nitrogenous waste)
uric acid, inhabits more arid environments, must conserve water
Fish (nitrogenous waste)
ammonia, has access to unlimited water, produces ammonia at the gills that is flushed away rapidly
Mammal (nitrogenous waste)
produce urea in urine, Similar to earthworm: water is an issue but not a problem
Factors affecting energy required for osmoregulation
Osmotic gradient to be overcome, Permeability of the animal's surface, Energetics of pumping solutes across body membranes
Ways an animal can gain water
By drinking, By osmosis (in fresh water), in diet, Metabolic water production
Ways an animal can lose water
By osmosis (in salt water), excretion, elimination, evaporation
Ways an animal can gain salts
Diffusion (in salt water), drinking, diet
Ways an animal can lose salts
Diffusion (in fresh water), sweating, excretion
Osmoconformers
Iso osmotic to environment (Many marine invertebrates)
Osmoregulators
Actively maintain internal osmolarity at level different from the environment (All** vertebrates occupying marine, freshwater and terrestrial environments except hagfish)
Advantage of osmoconformation
minimum energy required to control water movement
disadvantages of osmoconformation
With no mechanism to control osmolarity, changes in environmental conditions (increase or decrease in osmolarity) will cause a water gain or loss), Osmoconformers are reliant on environmental stability, do not have the option of colonizing freshwater or terrrestrial habitats