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 forms that is 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 function 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 vapours.
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
None of these
2. Which Vessel Transports Blood to Kidneys?
Both a) and 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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Fig: human urinary system
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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1. What is the Main Excretory Product in Human Beings?
Ans. 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?
Ans. Humans excrete Urea. Reptiles, birds, etc. excrete uric acid.
3. Which Living Being Produces Nitrogenous Wastes?
Ans. Generally mammals including humans, some fishes and amphibians are the main producers of nitrogenous wastes.