PART - 2 - Unit V : CH - 16 Excretory Products and Their Elimination — BIOLOGY STD 11 Science — Question
Rajasthan BoardEnglish MediumSTD 11 ScienceBIOLOGYPART - 2 - Unit V : CH - 16 Excretory Products and Their Elimination3 Marks
Question
Explain with examples the categories determined on the basis of nitrogenous excreting substances.
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Answer
There are categories determined on the basis of nitrogenous excreting substances : 1. Ammonia excretion (Ammonotelism) : Animals which excrete ammonia are called ammonotelic animals. Most of the groups of animals living in water are of this type, because the ammonia soluble in the aquatic environment goes into the aquatic environment through normal diffusion from the body. This method of excretion is called ammonia excretion. Examples : Amoeba, paramecium, bony fishes, tadpole larvae of frog etc. 2. Urea excretion (Ureotelism) : Animals which excrete nitrogenous waste products mainly in the form of urea are called ureotelic animals. In these animals, ammonia is produced during protein metabolism. This ammonia combines with $CO _2$ to form urea through the ornithine cycle. This work is completed by the liver. Some quantity of water is required to dissolve urea. Hence urea comes out in the form of liquid urine. It is less toxic. This method of excretion is called urea excretion. Examples : Adult amphibians, mammals and marine fishes etc. 3. Uricotelism : Animals which mainly excrete nitrogenous waste products in the form of uric acid are called uricotelic animals and this method is called uricotelism. Uric acid is almost insoluble in water. It gets precipitated in the kidney tubules and water from urine is reabsorbed by the kidney tubules, hence in these animals, uric acid is excreted in the form of a white and very thick paste. Thus it is helpful in water conservation. Examples : Reptiles, birds, insects and terrestrial snails etc.
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