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3.13 analyse information from secondary sources to compare and explain the differences in urine concentration of terrestrial mammals, marine fish and freshwater fish

analyse information from secondary sources to compare and explain the differences in urine concentration of terrestrial mammals, marine fish and freshwater fish

Some summary information is provided in the box below.

Excretory system of different animals (external website) Estrella Mountain Community College, Avondale, Arizona, USA

Type of organism Excretory product and concentration Environmental reason
terrestrial mammal
marine fish
freshwater fish

Summary: Differences in urine concentration of terrestrial mammals, marine fish and freshwater fish

Terrestrial mammals

Terrestrial mammals must work to find water and they are surrounded by air into which water quickly evaporates. Water conservation is of prime concern and these animals cannot excrete large quantities of water for the removal of metabolic waste.

Marine fish

The loss of water to the external environment is a problem that all marine fish must deal with. The marine environment in which the fish lives is hyperosmotic to the internal environment, i.e. there is a higher salt concentration in the water than inside the cells. This results in an osmotic gradient in which water is lost from the fish to the environment while ions are gained by diffusion. Ions are excreted by specialised glands.

Freshwater fish

The freshwater environment is hypo-osmotic to the internal environment of fish, i.e. there is a lower salt concentration in the water than inside the cells. This results in an osmotic gradient in which water is gained by the fish from the environment without drinking and salts are lost by diffusion. Ions are absorbed in the gut and by active uptake across the gills.