Nitrogen Excretion Flashcards
1
Q
How is ammonia excreted?
A
- NH3 out via gills
- diffuses out to mix with water
- NH3 + H20 = NH4 +OH
- Ammonia is in the form of glutarate when in the blood
- little energy needed to convert glutamate to ammonia but ammonia is very toxic
Example : Mainly fish and Invertebrates
2
Q
How is Urea Excreted?
A
In alkaline lakes there are not enough H= ions in the water to convert ammonia to ammonium so ornithine-urea cycle is used.
Example : Mammals, Amphibians, Fish in alkaline lakes
3
Q
Describe the Ornitin-Urea Cycle
A
Ornithine (PLUS HCO3- and NH3) –> Carbamyl phosphate –> Citrulline (PLUS Aspartate and 3ATP) –> Arginino Succinate (MINUS fumarate) –> Arginine (MINUS urea) –> Ornithine.
4
Q
How is Uric acid excreted?
A
Uric acid is excreted as a white powder by birds and reptiles ( a lot of energy is needed to produce uric acid from urea) However it is water insoluble and so reduces water loss. Low toxicity.
