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A Study on Various Modes of Excretion

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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. 

If you want a further reference on what excretion is, go through the rest of our study materials. If you want to master various other chapters of Biology, go through the rest of our study materials. Also, join our live classes through the Vedantu’s app today!

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.

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FAQs on A Study on Various Modes of Excretion

1. What is the main excretory product in human beings?

Urea is the main excretory product in human beings. However, the other major products are excess water and carbon dioxide. 

2. What do humans excrete, urea or uric acid?

Humans excrete Urea. Reptiles, birds, etc. excrete uric acid. 

3. Which living being produces nitrogenous wastes?

Generally mammals including humans, some fishes and amphibians are the main producers of nitrogenous wastes.

4. Which of the organs are involved in excretion?

Most excretory organs such as the skin, the kidneys, the lungs, intestines and the liver release toxins that the body needs to let go of.  These organs make up our excretory system. They each work independently without depending on the others.. Knowing which of the organs are involved in this process will help them understand the chapter in its entirety. Excretion gets rid of all the toxins that are present in the body and is one of the most vital bodily functions. The lungs remove carbon dioxide, the skin removes perspiration, the kidneys remove toxins and the intestines remove waste products from the body.

5. What is ureotelism?

Certain animals release urea through a process known as ureotelism. Ammonia converts into urea on metabolism in these organisms. The elimination of urea is mainly in various forms of nitrogen. It is in the form of semi solid or solid uric acid.  Urea happens to be a colourless component and gets formed when proteins produce amino acids after digestion takes place. 

6. How does excretion take place in humans?

Excretion in human beings takes place through the urinary system.  Some amount of excretion also takes place through the skin in the form of perspiration. The excretory system in the form of a pair of kidneys are located towards the back of the abdominal cavity. The kidneys filter blood removing all the toxins from the body.This platform only has the best of material and so, students will never feel misguided. 

7. Do plants also excrete?

Yes, plants are too excrete. They excrete through the stomatal pores that are present on leaves. Plants need to excrete excess carbon dioxide as well as oxygen. Carbon dioxide is a waste product of aerobic respiration whereas oxygen is a waste product of photosynthesis. Plants also excrete some of the waste substances into the soil that they’re surrounded with. They get rid of the water via transpiration. With the shedding of the leaves and bark, certain wastes get eliminated from the plants.