AMMONOTELISM

Introduction to Nitrogenous Waste Excretion

As body cells carry out metabolic activities, they consume oxygen and nutrients and produce waste products such as carbon dioxide, urea, and uric acid. Wastes must be eliminated from the body because they can be toxic to cells if they accumulate. The excretory system disposes of most of the wastes. The excretory system performs this function by removing wastes from the blood and excreting them into urine. There are various ways organisms eliminate metabolic waste products from their bodies. Different organisms have different modes of excretion like ammonotelism, ureotelism, and uricotelism, depending on their habitat and physiology.

What is Ammonotelism?

Ammonotelism is the process of excretion of nitrogenous waste in the form of ammonia. The organisms that excrete waste by ammonotelism are called ammonotelics. The excretion product, ammonia is highly toxic and produces ammonium hydroxide with water and is highly soluble in water. It must be eliminated from the body once it is formed.

Since ammonia can damage cells by alkaline reaction, excretion of ammonia needs a large quantity of water. In some invertebrates urea is hydrolyzed to carbon dioxide and ammonia. In fish and other amphibians, allenoate (salt or ester of allenoic acid) is turned into urea and glyoxylate.

Modes of Excretion Overview

There are five modes of excretion based on the product excreted.

• Ammonotelism - ammonia(highly harmful) excretion

• Uricotelism - uric acid excretion

• Aminotelism - amino acid excretion

• Ureotelism - urea excretion

• Guanotelism - guanine excretion

Mechanism of Ammonia Excretion

The mechanism of ammonia excretion is:

Diffusion Through Body Surfaces

Passive diffusion allows ammonia to move out through moist body surfaces when the surrounding ammonia concentration is low.

Gill-Based Excretion in Fishes

Most aquatic fishes eliminate ammonia mainly through their gills, where it diffuses easily into the water.

Direct Diffusion in Invertebrates

Many simple invertebrates like echinoderms and flatworms remove ammonia directly across their body surface.

Energy Requirement

Ammonia excretion requires the least energy because ammonia is highly soluble and can diffuse out without conversion.

Examples of Ammonotelic Animals

All ammonotelics are aquatic animals. Examples include:

• Larvae of amphibian

• Fishes

• Protozoans

• Cephalopods

• Echinoderms

• Platyhelminthes

Ammonotelism vs Other Modes

The difference between ammonotelism and other modes of excretion is discussed in the table below:

Excretion and its Importance

Excretion is the process of eliminating unwanted substances from the body, performed by the excretory system. Nitrogenous waste in the human body is urea. Extra nucleic acids and amino acids are broken by the liver. Urea is transported by the blood to the kidney. Kidney filters and waste is eliminated as urine. Major important functions of excretion are:

• Waste removal: By forming urine, the kidneys help excrete nitrogenous wastes from the body

• Osmoregulation: It helps in the regulation of pressure in fluid by the release of excess water.

• pH regulation: The kidneys excrete a variable amount of hydrogen ions into the urine and conserve bicarbonate ions, which are an important buffer of H+ in the blood. Both of these activities help regulate blood pH.

Ammonotelism NEET MCQs (With Answers & Explanations)

Important questions asked in NEET from this topic are:

• Modes of Excretion

• Ammonotelism vs Other Methods

Practice Questions for NEET

Q1. The most toxic nitrogenous waste excreted by many bony fishes, aquatic amphibians and aquatic insects is

1. CO2

2. Ammonia

3. Urea

4. Amino acids

Correct answer: 2) Ammonia

Explanation:

Ammonia is the most toxic excretory product.

Ammonia is extremely harmful to the body and is a consequence of protein metabolism. Fish and other aquatic species release ammonia straight into the water where it is diluted because it needs a lot of water to be safely expelled.

On the other hand, to save water and avoid toxicity terrestrial animals (including humans) transform ammonia into less harmful forms like urea or uric acid. Mammals can expel concentrated urea through urine, and it is less harmful than ammonia. Even less harmful uric acid is expelled as a paste to save water and is present in birds and reptiles.

Hence, the correct answer is option 2) Ammonia.

Q2. Assertion: Sharks are categorized as ammonotelic animals.

Reason: Sharks have the ability to retain significant amounts of ammonia in their blood.

1. Both the assertion and reason are true, and the reason is a correct explanation of the assertion.

2. Both the assertion and reason are true, but the reason is not a correct explanation of the assertion.

3. The assertion is true, but the reason is false.

4. Both the assertion and reason are false.

Correct answer: 4) Both the assertion and reason are false.

Explanation:

In this case, the assertion claims that sharks are categorized as ammonotelic animals. However, this assertion is false. Sharks are ureotelic animals, meaning they excrete urea as their primary nitrogenous waste product, not ammonia.

The reason given is that sharks have the ability to retain significant amounts of ammonia in their blood. This reason is also false. Sharks do not retain ammonia in their blood; instead, they convert ammonia into urea through their liver, which is then excreted.

Hence, the correct answer is Option (4) Both the assertion and reason are false.

Q3. Choose the incorrect statement

1. The process of excreting ammonia is Ammonotelism

2. Kidneys play any significant role in the removal of ammonia

3. Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions

4. Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic in nature

Correct answer: 2) Kidneys play any significant role in the removal of ammonia

Explanation:

Types of Animals Based on Excretory Wastes -

Ammonotelism:

• The process of excreting ammonia is Ammonotelism.

• Many bony fishes, aquatic amphibians and aquatic insects are ammonotelic in nature.

• Ammonia, as it is readily soluble, is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions.

• Kidneys do not play any significant role in its removal.

Hence, the correct option is Kidneys play significant role in the removal of ammonia

Also Read:

• MCQs on Types of Animals Based on Excretory Wastes

• Nephron

• Glomerular Filtration Rate