Question

What are the different modes of excretion in human beings?

Answer 1

Modes of excretion in human beings:

Ammonotelism:

1. Ammonia is excreted from the body.
2. It is produced by oxidative deamination of excess amino acids.
3. In an ammonotelic organism, ammonia is excreted in dilute solution form.
4. Only simple aquatic organisms can excrete ammonia as huge amounts of water (300-500 ml) are required for the excretion of ammonia.
5. Examples of ammonotelic organisms are simple aquatic invertebrates such as protozoa, sponges, jellyfish, etc.

Ureotelism:

1. Excretion of nitrogenous wastes like urea takes place.
2. Urea is produced through the detoxification of ammonia through the ornithine cycle.
3. Ureotelic organisms require much less water (50 ml) than ammonotelic organisms.
4. Examples of ureotelic organisms are amphibians like frogs and toads, mammals, cartilaginous fishes, etc.

Uricotelism:

1. These organisms excrete uric acid.
2. It is formed from ammonia and purines.
3. It is least soluble in water i.e. it requires only 10ml of water to dissolve.
4. Examples of uricotelic organisms are birds, insects, and some reptiles.

Aminotelism:

1. Amino acids are excreted without being metabolized.
2. Examples include certain molluscs and echinoderms.

Guanotelism:

1. Guanine is excreted as nitrogenous waste.
2. It also contains insoluble crystals of uric acid and urates.
3. Examples of organisms are scorpions, spiders, lizards, and birds.