All organisms release by-products due to many different processes in their body. Plants excrete out extra water by transpiration and guttation or in the form of waste substances like resins, sap and latex. Animals excrete solid as well as liquid substances.
The food eaten by animals is digested using enzymes and acids in the stomach and intestine. When the nutrients and water are absorbed, the food material is turned into faeces and excreted through the anus. The liquid substances are excreted in the form of urine. Birds, insects and reptiles minimise water loss by excreting wastes in semi-solid pellets.
Types of nitrogenous wastes
- Ammonia- The animals that excrete waste products in ammonia are called Ammonotelic. Ammonia is the most toxic waste product requiring large amounts of water to be washed off. Aquatic animals usually show Ammonotelism.
- Urea- The animals that excrete waste in the form of urea are called Ureotelic. Urea is less toxic than ammonia and can be stored in the body for some time. Humans, Frogs, and Turtles show Ureotelism.
- Uric acid- The animals that excrete waste in uric acid are called Uricotelic. Animals that live in deserts or dry climates like birds, lizards, and snakes excrete uric acid as pellets.
Ammonotelism
Waste materials are produced due to food digestion and protein degradation, including several nitrogen-containing compounds, including ammonia, uric acid and urea. Long-term dehydration can cause nitrogen waste to build up, leading to fatal consequences if not excreted. Aquatic species like poriferans, protozoans, amphibians, cephalopods and bony fishes typically excrete ammonia.
Ammonia is removed from the body in the form of ammonium ions. If enough water is available, the small molecules of ammonia can easily diffuse through the body’s surface and gills. Still, the kidneys are ineffective at eliminating ammonia from the system.
Animals cannot withstand even mild concentrations of ammonia in their bodily fluids because ammonia is extremely poisonous. When the concentration of ammonia in the water is already significant, animals cannot excrete ammonia in the water as it is already saturated. Hence they are forced to move toward terrestrial habitats. Since urea or uric acid are less poisonous forms of nitrogen, it is more likely to be excreted during the shift to land from water. The least hazardous nitrogenous by-product is uric acid. Terrestrial animals and mammals usually excrete urea.
FAQ: What is Ammonotelism
Q.1 What are the different types of excretory products?
A.1. Animals get rid of nitrogenous wastes from their body in different forms. Nitrogenous substances may be excreted as Ammonia, Urea or Uric acid.
Q.2 What are Ammonotelic organisms?
A.2. The organisms which remove nitrogenous wastes from their body in the form of Ammonia or Ammonium ions are called Ammonotelic organisms. This method of excretion is called Ammonotelism.
Q.3. Which organisms exhibit Ammonotelism?
A.3. Aquatic organisms like aquatic insects, poriferans, protozoans, cephalopods, cartilaginous and bony fishes and amphibians show ammonotelism.
Q.4. Why do terrestrial animals not excrete waste as Ammonia?
A.4. Ammonia is the most toxic form of nitrogenous waste and requires huge amounts of water to be removed from the system. Terrestrial animals cannot access such large amounts of water due to their habitat and water scarcity on land.
Hence they have adapted themselves to convert ammonia into a less toxic form known as urea. Urea can be excreted out even in less water, thereby preventing the accumulation of harmful nitrogenous wastes. If ammonia accumulates in the body, it forms ammonium hydroxide which is caustic and damages the cells.
Q.5 How is Ammonia excreted out?
A.5. Ammonia is excreted as Ammonium ions () which easily dissolve in a large amount of water. It can pass out of the body by diffusion through gills and skin when the animal is submerged in water.
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