Chapter 44 – Osmoregulation and Excretion
Osmoregulation is regulation of solute concentrations and water balance by a cell or
Osmoconformer: An animal that is isoosmotic with its environment.
Osmoregulator: An animal that controls its internal osmolarity independent of the
Stenohaline: Referring to organisms that cannot tolerate substantial changes in external
Euryhaline: Referring to organisms that tolerate substantial changes in external
Most marine animals are osmoconformers. Most marine chordates are osmoregulators.
Excretion is the disposal of nitrogencontaining metabolites and other waste products.
• Disposal of metabolic wastes
o Nitrogenous waste
When amino acids and nitrogenous bases are not being used they are broken down and
used to make ATP. In order to do this, the amino group needs to be removed. Most
aquatic animals produce ammonia. Mammals, most amphibians and sharks make Urea.
Many reptiles, birds, insects etc., makes Uric Acid.
Ammonia: Toxic at low concentrations flushed from body with copious water.
Ex: sponges, cnideria
Urea: Requires energy to produce, but is less toxic and therefore can tolerate higher
concentrations. Producing Urea helps us retain water because it doesn’t need the water to
be flushed out.
Uric Acid: Requires even more energy to produce than Urea. Uric acid is relatively
insoluble in water and therefore can be excreted with a paste without water loss.
Steps to system:
4. Excretion Platyhelminthes Excretory system
Has protonephridia, which contains tubules. The fluid moves through the tubule into the
flame tube where is filtered. Ciliate are moving it through the filter and then back into the
tubule which leads to pores in the “skin”
Metanephridia has the fluid flowing