Excretory Products and Their Elimination - Modes of excretion (Ammonotelism, Ureotelism, Uricotelism)
Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Nitrogenous waste products are formed primarily from the catabolism of proteins and nucleic acids, resulting in , urea, and uric acid.
Ammonotelism: The process of excreting ammonia (). It is highly toxic and requires a large volume of for elimination (approx. of per gram of ).
Ammonia is generally excreted by diffusion across body surfaces or through gill surfaces (in fish) as ammonium ions ().
Ureotelism: Terrestrial adaptation necessitates the production of less toxic nitrogenous wastes like urea () to conserve .
In ureotelic animals, produced by metabolism is converted into urea in the liver via the Ornithine cycle (Urea cycle) and released into the blood.
Uricotelism: The excretion of uric acid () in the form of pellets or paste with minimum loss of . It is the least toxic nitrogenous waste.
Comparison of Toxicity: .
Comparison of Water Requirement for excretion: .
📐Formulae
💡Examples
Problem 1:
A tadpole excretes , but an adult frog excretes urea. Explain the physiological transition.
Solution:
Tadpoles are aquatic and have access to abundant , allowing them to be ammonotelic. Adult frogs are semi-terrestrial; to conserve , they transition to ureotelism, converting to urea.
Explanation:
The mode of excretion depends on the availability of . Ammonia requires high for dilution, while urea requires significantly less.
Problem 2:
Identify the mode of excretion for the following organisms: (i) Bony fishes, (ii) Birds, (iii) Mammals.
Solution:
(i) Bony fishes: Ammonotelism; (ii) Birds: Uricotelism; (iii) Mammals: Ureotelism.
Explanation:
Bony fishes live in water and can flush out . Birds need to conserve and reduce weight for flight, so they excrete uric acid paste. Mammals convert to urea as a compromise between toxicity and water loss.
Problem 3:
Why is uric acid excretion considered a terrestrial adaptation?
Solution:
Uric acid () is nearly insoluble in and is the least toxic.
Explanation:
This allows animals like reptiles and insects to eliminate waste with negligible loss, which is critical for survival in arid terrestrial environments.