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Nutrient cycle in environment

  BIO-GEO CHEMICAL CYCLE OR NUTRIENT CYCLE       Bio  -    Living organism       Geo  -    Rock, Soil, Air, Water Chemical   -  Material or Nutrients        Cycle   -   Path All the types of material required by ecosystem in addition of energy, are available continuously to system through recycling. Thus there is a constant exchange of materials between the living organism and their abiotic environment through the recyling of materials. This phenomenon is called Bio-geo chemical cycle. Note: Environment factors,e.g soil , moisture, ph, temperature etc, regulate the release of nutrients into the atmosphere. Biochemical cycle The following types of cycle are found in an ecosystem. (i) Gaseous Cycle - C, H, N. O cycles. Reservoir is in the atmosphere (air) or in Hydrosphere(water). Sedimentary cycle - P. S, Ca cycles reservoirs are in earth's crust (lithosphere). Note : In these cycles, the bulk material remains in the inactive reservoir on earth crust like sediment of sea, or water
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ELIMINATION OF NITROGENOUS WASTES


Ammonia, urea and uric acid are the major forms of nitrogenous wastes excreted by the animals. 

Ammonia is the most toxic form and requires large amount of water for its elimination, whereas uric acid, being the less toxic, can be removed with a minimum loss of water.

On the basis of type of excretory products (ammonia, urea and uric acid, three types of animals are present)

Ammonotelics : Most aquatic animals excrete nitrogenous waste as ammonia. Ammonia is readily solutie soluble so generally it is excreted by diffusion across body surfaces or thought gill  surfaces (in fish) as ammonium in

Kidney do not play significent role in its removal

e.g. of ammonotelic animals are teloest (many bony fish), aquatic amphibians (tadpoles), aquatic reptiles and aquatic insects etc.

Ureotelics : Animals like mammals, many terrestrial amphibians, marine fish excrete urea and are called

Ureotelic. Ammonia produced by metabolism is converted into urea in the liver of these animals and released into the blood which is filtered and excreted out by the kidneys. Excretion of urea is benefical for these animals than ammonia because of following reason

1. Urea can be tolerated in much more concentrated form because it is 100000 times less toxic than ammonia,

2. Urea excretion helps to sacrifice less water while disposing off the nitrogenous wastes.

In mammals urea is excreted by kidney. However entire amount of urea produced is not excreted

immediately but some portion of it is retained in the kidneys for osmoregulation. (important for water reabsorption)

Sharks retain some amount of urea produced to balance the osmolarity of body fluids with surrounding

sea water. Thus urea here acts as an osmolyte.


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