Question

Write the classification of animals on the basis of the excretory substance.

Answer 1

Excretion is defined as the elimination of metabolic wastes by an organism at exchange boundaries.

Complete answer: During catabolic activities of the body, the energy is produced which is utilized in performing different vital activities. Along with these activities, certain waste products are also produced.
These products are harmful to the body and affect cellular activities adversely.
The elimination of such waste products from the body is known as “excretion”.
Skin, liver, lungs, large intestine, and kidneys are the excretory organs of the body.
The excretory organs along with the elimination of waste products also help in performing the osmoregulatory function of the body.

The catabolic activities of carbohydrates and fats result in the production of CO2 and water as a waste product, whereas the main excretory products are formed due to the breakdown of proteins.
1. The elimination of the excess nitrogen in the form of ammonia is known as ammonotelism. Ammonia is a toxic substance which has a great solubility in water.
2. Ureotelic animals-When the main excretory product is urea then the phenomenon is ureotelism.
3. The main excretory product is uric acid. It is synthesized by ammonia in the liver. It is far less toxic than urea and ammonia. E.g. gastropod, reptiles, birds, insects, etc.
4. The protozoans have the contractile vacuoles as the organs of osmoregulation. In coelenterates, the excretory products are expelled in the coelenteron.
5. The flame cells are the unit of excretion in flatworms whereas nephridia form the excretory system of the annelids.
6. The green glands are the excretory organs of prawn and crabs but malpighian tubules perform the excretion in the insects and arachnids. They are provided with numerous sweat glands. The secretion of sweat glands has nearly the same composition as that of urine.

Note: The most common sources include dairy shed effluent (containing urine, dung, wash water, residual milk, and wasted feed), dairy manure, poultry litter (a mix of manure, water, spilled feed, feathers, and bedding material), renderings, and other wastes from livestock finishing operations.