Question

Compare and contrast nephron organization among each vertebrate group. Explain why there are large differences among the nephron organizations of marine, freshwater, and terrestrial vertebrates.

Answer 1

Answer:

There is progressive change in excretory organs and nephron from lower to higher vertebrates.Many fishes excrete ammonia by diffusion through skin surface and also by gill surface. Amphibians , mammals have kidneys to excrete urea after filtration. Birds and reptiles excrete uric acid crystals by kidney. Kidneys are tubular structures made up of nephrons ,works for excretion.

Kidneys are of three types based on complexity:

1) Pronephros.

2) Mesonephros.

3) Metanephros.

Pronephros is the simplest one found in lower vertebrates.

Mesonephric kidney found in Amphibians.

Metanephric kidney is found in higher vertebrates like mammals and birds.

* The complexity of kidney and type of excretory product ,depends on the environment and temperature changes, fresh water and marine fishes have regulatory mechanisms for water and ion exchange.Aquatic organisms excrete ammonia in dilute form due to good availability of water. Terrestrial mammals and birds excrete urea and uric acid respectively.

Urea is less toxic and require small amount of water. Uric acid is least toxic and excreted in solid form ,requiring least amount of water.

Hence, terrestrial and aquatic organisms are well adapted to their surroundings.