Types and Process of Excretion in Animals and Humans
The excretion definition in biology states that it is the process of expelling metabolic wastes from living organisms. All animals, including humans, consume food to survive. Afterwards, several biochemical reactions take place within the body.
During the process some toxic by-products form that are harmful. Hence, the bodies release those products through excretion.
Different animals use different organs to continue this process. For humans, the major excretory organs are liver, lungs, large intestine, kidneys and skin. Following is the list of each of these organs functioning in excretion.
Kidneys regulate urinary systems.
The large intestine removes solid wastes, resulting from the digestion of food.
The lungs breathe out carbon dioxide and water vapors.
The liver deaminates excess amino acids in the blood.
The skin releases salt and excess water through sweat.
To know more about what excretion is, read this piece.
Methods of Excretion
Each living being follows distinct modes of excretion. However, some significant types are mentioned below.
Ammonotelism – It is the procedure of removing ammonia. Several aquatic insects, amphibians and bony fishes show Ammonotelic nature. Since ammonia is easily soluble, a few diffusions across the body surface are enough to drive away this substance. However, in the case of fishes, the gill surface does the same, releasing ammonium ions. It comprises the most toxic excretion in animals.
Ureotelism – Several Ureotelic animals like mammals, marine fishes, terrestrial amphibians, etc. release Urea using this process. Due to metabolism, ammonia converts into Urea in the liver of these animals, which is finally mixed in blood. Following that, the kidneys filter the blood to eliminate the waste. However, some of the urea content can remain in the kidneys that later help in maintaining osmolarity. Moreover, the most crucial nitrogenous waste in humans is Urea which is released through urine.
Uricotelism – Some animals like birds, reptiles, insects, land snails, etc. eliminate nitrogenous wastes in the form of uric acid. This whole process takes place with a loss of minimum water. Uric acid is the least toxic among other excretions.
Aminotelism – This process occurs in some echinoderms and molluscs. Amino acids are excreted by it.
Guanotelism – Animals like Scorpio, spiders, etc. excrete guanine (uric acid) using this process. It is insoluble and non-toxic. This excretory substance comes out in solid forms. Most animals of arid areas adapt to this excretion.
Do it Yourself
1. Excretion in Amoeba occurs through
a. Diffusion
b. Infusion
c. Uricotelism
d. None of these
2. Which Vessel Transports Blood to Kidneys?
a. Renal vein
b. Renal arteries
c. Both a) and b)
d. Only b)
Answers: 1-a), 2-b)
Excretion in Human
The type of excretion in humans includes the urinary system. However, skin also helps in evaporating excess water and salt through sweat glands. The entire process of formation of urine takes place in the kidney. Every day the kidneys filter approximately 180L of blood.
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The urine formation takes place in three steps. They are Glomerular filtration, absorption and secretion. Urine contains substances like Urea, potassium, sodium, creatinine, chloride and other dissolved ions. Human excretory system is a vital topic when you have to study what excretion is.
DIY: Draw a table and write down the differences between excretion and secretion.
Some Examples of Excretions
Below are a few examples of excretion in different organisms.
Amoeba excretes through its body surface.
Molluscs use nephridia as an excretory organ.
The physiology of excretion in insects includes Malpighian tubules. For example, cockroaches, grasshoppers, etc.
A kidney is the main excretory organ of almost all vertebrates.
Flatworms excrete through protonephridia.
Question: What is excretion in plants? Elucidate with examples.
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Importance of Excretion in Living Organisms
Releases toxins from the body
Lessens anxiety and the stress levels
Regulates the body temperature
Regulates the blood pressure levels
Helps the organs perform all bodily functions in a proper manner
Improves the menstrual health in women
Relieves one from chronic constipation
How to Study for Excretion from Vedantu
Vedantu has pertinent study material on Excretion and all students who need to understand the topic can read the page that’s there. The page is in the name of Modes of Excretion - Methods, Organs with Functions and Examples
This page is an ideal guidebook and has relevant matters on Excretion. Students can go through this page and make notes. They can mark all the pointers that seem important to them and then revise those before a test on the subject.
FAQs on Modes of Excretion in Living Organisms
1. What are the modes of excretion in animals?
The modes of excretion in animals are the different ways by which organisms remove metabolic wastes from their bodies. These modes are mainly classified based on the type of nitrogenous waste excreted.
- Ammonotelism – Excretion of ammonia (seen in many aquatic animals like bony fishes).
- Ureotelism – Excretion of urea (seen in mammals, including humans, and adult amphibians).
- Uricotelism – Excretion of uric acid (seen in birds, reptiles, and insects).
2. What is ammonotelism?
Ammonotelism is the mode of excretion in which organisms eliminate nitrogenous waste mainly in the form of ammonia. Ammonia is highly toxic but highly soluble in water.
- Common in aquatic animals like bony fishes and many aquatic invertebrates.
- Requires large amounts of water for dilution.
- Ammonia diffuses directly into surrounding water through gills or body surface.
3. What is ureotelism?
Ureotelism is the mode of excretion in which nitrogenous waste is excreted mainly as urea. Urea is less toxic than ammonia and requires moderate water for excretion.
- Common in mammals, including humans.
- Also seen in adult amphibians and cartilaginous fishes.
- Urea is produced in the liver through the urea cycle and eliminated by the kidneys.
4. What is uricotelism?
Uricotelism is the mode of excretion in which nitrogenous waste is eliminated mainly as uric acid. Uric acid is least toxic and almost insoluble in water.
- Common in birds, reptiles, and insects.
- Requires very little water for excretion.
- Excreted as a semi-solid paste to conserve water.
5. What is the difference between ammonotelism, ureotelism, and uricotelism?
The difference between ammonotelism, ureotelism, and uricotelism lies in the type of nitrogenous waste excreted and the amount of water required.
- Ammonotelism: Excretes ammonia; highly toxic; needs large water; seen in aquatic animals.
- Ureotelism: Excretes urea; moderately toxic; needs moderate water; seen in mammals.
- Uricotelism: Excretes uric acid; least toxic; needs minimal water; seen in birds and reptiles.
6. Why do aquatic animals excrete ammonia?
Aquatic animals excrete ammonia because it can be easily diluted and removed in a water-rich environment. Ammonia is highly toxic but dissolves readily in water.
- Water continuously washes ammonia away from the body.
- It diffuses across gills or body surface.
- It requires very little energy to produce.
7. How does the human body excrete nitrogenous waste?
The human body excretes nitrogenous waste mainly in the form of urea through the kidneys. Humans are ureotelic organisms.
- Ammonia formed during protein metabolism is converted to urea in the liver.
- Urea is transported to the kidneys via blood.
- It is filtered and removed as urine.
8. What are nitrogenous wastes in excretion?
Nitrogenous wastes are metabolic by-products formed during the breakdown of proteins and nucleic acids. The main nitrogenous wastes are:
- Ammonia – Highly toxic and water-soluble.
- Urea – Less toxic and moderately soluble.
- Uric acid – Least toxic and poorly soluble.
9. Why is uricotelism important for birds and reptiles?
Uricotelism is important for birds and reptiles because it conserves water and is safe for embryonic development in eggs. Uric acid is almost insoluble and forms a semi-solid paste.
- Prevents water loss in dry habitats.
- Allows storage of waste inside eggs without toxicity.
- Reduces body weight in birds by minimizing water content.
10. How are modes of excretion related to habitat?
Modes of excretion are closely related to habitat because water availability influences the type of nitrogenous waste produced. Different environments demand different adaptations.
- Aquatic animals: Ammonotelic due to abundant water.
- Terrestrial mammals: Ureotelic to balance toxicity and water loss.
- Desert animals and birds: Uricotelic to conserve maximum water.
