Lab 6
PRACTICAL 6:
OSMOREGULATION AND EXCRETION
Introduction
Many animals need to control the water content of their body because the concentration of their body fluids is different to that of their environment. The process by which the amount of water and concentration of soluble ions in the body are regulated is called osmoregulation. In most cases the organs which are responsible for osmoregulation are also involved in the excretion of metabolic waste products.
In this practical you will conduct an experiment to determine the osmoregulatory ability of two organisms. You will also examine the organs responsible for osmoregulation and excretion of both invertebrates and vertebrates.
1.
Osmoregulation Experiment
Phascolosoma lurca (Phylum Sipuncula) and Uca coarctata, fiddler crab (Subphylum Crustacea) occur throughout the year in the mudflats of Suva Points, Nasese, and generally around all river mouths and in the mudflats throughout Fiji. In these environments the water salinity can vary dramatically from time to time. Salinity can be close to freshwater (low salinity) after heavy rains, especially around the river mouths and estuaries. During the dry season the salinity would be same as seawater salinity. In addition the environment also undergoes daily tidal changes. By occupying these habitats, P. lucra and U. coarctata obviously tolerate a wide salinity range. However, it is anticipated that P. lucra being soft-bodied and related to annelids, tends towards osmoconforming; while U. coarctata, having a thick cuticle, tends towards osmoregulating over a range of salinities.
This experiment is designed to test the hypothesis that P. lurcra is an osmoconformer and U. coarctata is an osmoregulator.
The method used the density of extrcellular fluid (ECF) as a measure of ionic and osmotic concentration. All body fluids are more dense than water since they consist of water (SG=1) plus solutes. Increased solute concentration causes an
OSMOREGULATION AND EXCRETION
Introduction
Many animals need to control the water content of their body because the concentration of their body fluids is different to that of their environment. The process by which the amount of water and concentration of soluble ions in the body are regulated is called osmoregulation. In most cases the organs which are responsible for osmoregulation are also involved in the excretion of metabolic waste products.
In this practical you will conduct an experiment to determine the osmoregulatory ability of two organisms. You will also examine the organs responsible for osmoregulation and excretion of both invertebrates and vertebrates.
1.
Osmoregulation Experiment
Phascolosoma lurca (Phylum Sipuncula) and Uca coarctata, fiddler crab (Subphylum Crustacea) occur throughout the year in the mudflats of Suva Points, Nasese, and generally around all river mouths and in the mudflats throughout Fiji. In these environments the water salinity can vary dramatically from time to time. Salinity can be close to freshwater (low salinity) after heavy rains, especially around the river mouths and estuaries. During the dry season the salinity would be same as seawater salinity. In addition the environment also undergoes daily tidal changes. By occupying these habitats, P. lucra and U. coarctata obviously tolerate a wide salinity range. However, it is anticipated that P. lucra being soft-bodied and related to annelids, tends towards osmoconforming; while U. coarctata, having a thick cuticle, tends towards osmoregulating over a range of salinities.
This experiment is designed to test the hypothesis that P. lurcra is an osmoconformer and U. coarctata is an osmoregulator.
The method used the density of extrcellular fluid (ECF) as a measure of ionic and osmotic concentration. All body fluids are more dense than water since they consist of water (SG=1) plus solutes. Increased solute concentration causes an
References: (some suggestions) Lockwood, A.P.M. (1963) Animal body fluids and their regulation. London: Scholarship Series, Heinemann. Potts, W.T.C. & G. Parry (1964) Osmotic and ionic regulation in animals. Oxford, Pergamon Press. Villee, C.A., W.F. Walker Jr. & R.D. Barnes (1973) General Zoology, Sixth edition. Philadelphia: Saunders 97, 205, 566, 587. (plus any general or comparative text or animal physiology). 3 (Lab BI108)