Modes of excretion vary according to the waste product generated. The majority of the food is digested and used by the body to produce energy; the rest is removed from the body by the excretory system in the form of urine and faeces.
- The biological process of excretion involves the Urethra.
- It allows an organism to eliminate excess waste materials and nitrogenous metabolic byproducts.
- Carbon Dioxide from cellular respiration is also a waste product.
- Urea from protein, ammonia, and uric acid from nucleic acid are some of the waste products.
Also read: NCERT Solutions for Class 12 Biology
| Table of Content |
Key terms: Modes of excretion, Excretion, Metabolic process, Waste products, Uric acid, Kidney, Waste, Nitrogenous waste.
What is Excretion?
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It is the term used to describe the removal of metabolic wastes by an organism. The byproducts of metabolism include nitrogenous substances (urea), carbon dioxide (CO2), Bilirubin, Too much water, Inorganic salts, etc. Egestion (defecation) and secretion are different from it.
Significance of Excretion
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Excretion has the following significance for the body.
1. Elimination of metabolic waste products
The metabolism of carbohydrates and lipids yields CO2 and H2O, respectively. In the cell and tissue, protein metabolism results in nitrogenous wastes that are eliminated through excretion.
2. Getting rid of toxic waste
The accumulation of excretory products, such as nitrogenous wastes, CO2, colors created by hemoglobin breakdown, medicines, etc., is bad for the body. These dangerous wastes are thus eliminated.
3. Osmoregulation of the body
It aids in regulating the body's water content as well as keeping a steady ionic concentration of body fluid.
Other significance involves Control of PH in the body and temperature.
Also read: Mechanism of Excretion in Plants
Modes of Excretion
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Every living being has a different method of excretion. However, some significant types are mentioned below.
1. Ammonotelism
Ammonotelism is a method of elimination in which ammonia is the main waste product. And the creatures that use this strategy are referred to as ammonotelic.
- This category includes a sizable number of fish, plasmodia, echinoderms, poriferans, and arthropods.
- Aquatic animals excrete ammonia directly into their ecosystem, where it quickly disperses.
- It is extremely toxic to tissues.
- Moreover, ammonia damages cells through the corrosive reaction of the alkaline and generates ammonium hydroxide.
- That is highly water-soluble.
- Consequently, a lot of water is needed for the safe expulsion of ammonia.
2. Ureotelism
The process of excretion in which nitrogenous waste is eliminated as urea is known as ureotelism.
- In comparison, urea is less hazardous to the body.
- Urea is excreted by urine, making humans ureotelic.
- Moreover, urea is less toxic than ammonia.
- Numerous ureotelic species, including mammals, marine fish, terrestrial amphibians, etc., release urea by this mechanism.
- These animals' livers undergo a metabolic process that turns ammonia into urea.
- It is then combined with their blood.
- In order to remove the waste, the Kidney filters the blood after that.
3. Uricotelism
Uricotelism is the mechanism of excretion in which nitrogenous waste is eliminated as uric acid. Uricotelic animals are those that use this form of excretion. Although this process is the most taxing metabolically, it also loses the least amount of water and is the least toxic. Moreover, the excreta turns into pasty, colorless suspensions because uric acid doesn't dissolve right away in water. The majority of insects, avians, and reptiles are classified as uricotelic.
4. Aminotelism
Certain molluscs and echinoderms go through this process. It releases amino acids into the body. These species have a process of excretion known as aminotelism, and they are aminonotelic.
5. Guanotelism
It is non-toxic and insoluble. Solid forms of this excretory material are produced. Most arid-area animals are accustomed to this discharge. Before excretion, spiders turn the ammonia into guanine. Other animals with this trait include some birds, earthworms, and reptiles.
- Even plants produce waste that is eliminated from the plant body differently than it is done by living things.
- For instance, they produce solid wastes that build in the bark of the trees and emerge as resin, latex, etc.
- They produce gaseous wastes that are directly expelled into the atmosphere.
Without excretion, a vital living mechanism, the body starts to deteriorate and decompose from the high amounts of toxins that inhibit cellular growth and repair.
Also read: Excretory products and their elimination MCQ
Examples of Excretion
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Examples of excretion from various creatures are:
- Amoeba excretes via the surface of its body.
- Nephridia are used as an excretory organ by molluscs.
- The Malpighian tubules are a part of the excretion physiology in insects. Cockroaches, grasshoppers, etc. are a few examples.
- The primary excretory system of almost all vertebrates is the kidney.
- Protonephridia are used by flatworms to defecate.
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Things to Remember
- Excretion is removal of waste products from the body.
- Modes of excretion depend on the type of waste products.
- Organs involved in the body's excretory system include the skin, liver, and lungs.
- Animals use a variety of excretion processes to eliminate waste that contains nitrogen.
- Ammonia excretion is the subject of ammonotelism.
- Animals differ in the types of nitrogenous waste they produce, including urea, ammonia, and uric acid (mammals, aves, fishes, amphibians, insects)
- The kidneys, urinary bladder, urethra, and two ureters make up the human excretory system.
- Animal bodies would produce waste products as a result of metabolic processes.
- Carbon dioxide is also a waste product that is removed by the respiration system.
Sample Questions
Ques. Which compounds pass through the skin for excretion? What is the skin's excretory product? (3 marks)
Ans. When we are excessively hot, our skin discharges sweat and perspiration through tiny holes called pores, which play a part in the excretory system. One way the body cools down and contributes to homeostasis is through sweating. Heat is removed from the body when sweat droplets form on the skin's surface because the water evaporates. Sweat, water, sodium chloride, and other wastes are expelled from the skin.
Ques. What is the function of the excretory system? (5 marks)
Ans. Important function of the excretory system is mentioned below.
- Wastes that are toxic and nitrogenous are eliminated by the excretory system.
- The excretory system rids the body of these nitrogenous wastes as well as surplus salt and water.
- Cells produce water and carbon dioxide as waste as they break down carbohydrates during cellular respiration.
- The excretory system helps to regulate blood pressure.
- The urinary system regulates the production of red blood cells by producing the hormone erythropoietin, which also helps to maintain the body's fluid balance.
Ques. Which organ is in charge of the body's carbon dioxide removal? (1 mark)
Ans. Expiration is the process by which carbon dioxide, a gaseous waste product, which is present in excess, is expelled through the lungs.
Ques. Write some examples of excretion in various animals. (4 marks)
Ans. Below are the examples of excretion.
- Amoeba excretes through its surface.
- Molluscs use nephridia as an excretory organ.
- The excretion physiology of insects includes the Malpighian tubules.
- Examples include grasshoppers, cockroaches, and other insects.
- The kidney is practically every vertebrate's main excretory organ.
- Flatworms use protonephridia to urinate.
Ques. What transpires when a living organism lacks an excretory system? (4 marks)
Ans. The waste products that accumulate from digestion and cell activity must be expelled by your body. If these wastes are not eliminated, your cells may stop functioning, which could cause serious illness. This illness may possibly be lethal. Your excretory system's organs assist in the body's waste elimination process.
The body starts to degenerate and break down because of the excessive levels of toxins that prevent cellular growth and repair without elimination, a crucial life mechanism.
Ques. What is aminotelism? (2 marks)
Ans. Certain echinoderms and molluscs experience this process. It causes the body to release amino acids. These organisms are aminonotelic and have a process of excretion known as aminotelism.
Ques.What are nitrogenous waste? (1 mark)
Ans. As a result of cellular metabolic processes, nitrogenous wastes are created. Ammonia, urea, and uric acid are the most prevalent metabolic wastes.
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