Excretory Products and Their Elimination

Edited By Irshad Anwar | Updated on May 27, 2025 11:42 AM IST

The excretory system plays a vital role in maintaining homeostasis, which means keeping the internal environment of the body stable and balanced. The process known as excretion involves the removal of metabolic waste products, such as urea, carbon dioxide, and excess salt, from the body to prevent harm and ensure proper functioning.

This Story also Contains

What is Excretion?
What Are Excretory Products?
Excretory Systems in Different Organisms
The Human Excretory System
Diseases of the Excretory System
Role of the Excretory System in Osmoregulation
Tips, Tricks, and Strategies to Prepare For Excretory Products and Their Elimination
Weightage of Topics in Different Entrance Exams
Types of Questions Asked on the Topic in Different Exams
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Excretory Products and Their Elimination

In this chapter, students will explore the types of waste products, organs involved in excretion and the structure and function of the human excretory system. It also explains how different organisms eliminate waste in various ways, giving a clear understanding of how excretion supports both survival and overall health. This is an important chapter of Biology and is important for exams like NEET.

What is Excretion?

The term excretion refers to the biological processes of elimination whereby organisms remove waste coming from metabolic activities. This vital function prevents the accumulation of toxic substances that might damage to cellular processes. The excretory system regulates the amount and concentration of body fluids, eliminates metabolic wastes, and also helps maintain the correct pH level.

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What Are Excretory Products?

Excretory products can be categorised broadly into two categories:

Metabolic Waste Products:

Urea: It is produced by the combination of ammonia in the liver; less toxic to the system than ammonia.
Uric Acid: It is a waste product produced due to nucleotide deamination; less soluble in water.
Ammonia: This is highly toxic and a waste product of protein breakdown; the excretory product of most aquatic animals.
Carbon Dioxide: It is breathed out as a product of cellular respiration.
Water: Lost through urination, sweat, and respiration.

Non-Metabolic Waste Products

Bile Pigments: A product of the breakdown of haemoglobin.
Excess Salts: Eliminated to maintain the electrolytes within normal ranges.

NCERT Notes Subject Wise Link:

Excretory Systems in Different Organisms

Diverse organisms have different excretory systems based on their habitat and lifestyle:

Single-celled Organisms:

Protozoa: Contain a contractile vacuole that gets rid of waste products.
Hydra: Uses diffusion for waste removal.

Invertebrates

Earthworms: Use nephridia for removing waste.
Insects: They have Malpighian tubules with which they secrete waste. Example- Phylum Arthropoda.

Vertebrates:

Fish: The system relies on gills and kidneys to excrete ammonia (ammonotelic organisms).
Amphibians: The system depends on the skin and kidneys to excrete urea (ureotelic organisms).
Reptiles and Birds: They primarily utilise the kidneys and cloaca to excrete uric acid (uricotelic organisms).
Mammals: The system uses the kidneys, which extract the waste products from the body and excrete them as urea (ureotelic organisms).

The Human Excretory System

The human excretory system consists of several organs that work together to remove waste products from the human body:

Parts:

Kidneys: The system filters blood and comes out as urine.
Ureters: The system removes urine from the kidneys to the bladder.
Urinary Bladder: The system holds urine in the bladder until it is expelled from the body through excretion.
Urethra: The tube through which urine comes out of the body.

Nephron

Nephrons are the basic structural and functional units of the kidneys in the human excretory system. Each kidney contains about 1 million nephrons and is responsible for filtering blood and forming urine. Nephrons consist of a Bowman's capsule surrounded by a network of capillaries called the glomerulus, followed by the long tubular proximal convoluted tubule, loop of Henle, distal convoluted tubule and collecting duct. The nephron perform processes like filtration, absorption, secretion and excretion to remove waste while retaining the useful substances.

Hormones that Control Urinary Secretion

ADH (Anti-diuretic hormone): It regulates water reabsorption in the kidneys.
Aldosterone: It influences sodium reabsorption.

Other Excretory Organs in Humans

Besides kidneys, human beings have many other organs that help in excretion:

Skin: Sweat glands remove water, salts, and minute amounts of urea.
Lungs: Release carbon dioxide and water vapour during respiration.
Liver: Converts ammonia to urea and breaks down haemoglobin to form bile pigments.

NCERT Exemplar Solutions Subject-wise link:

Diseases of the Excretory System

The excretory system can be affected by a range of diseases:

Kidney stones: Concentrated minerals that cause pain and blockage.
Urinary tract infection (UTI): Bacterial infection of the urinary system.
Glomerulonephritis: Inflammation of the kidney glomeruli.
Chronic kidney disease (CKD): Slow progression of kidney function loss.

Role of the Excretory System in Osmoregulation

Osmoregulation is the maintenance of water and electrolyte balance in an animal's body. The excretory system maintains:

Proper salt-water balance.
Adaptations range from simple diffusion in unicellular organisms to the most complex systems in vertebrates.
Surviving both in freshwater and terrestrial habitats.

NCERT Solutions Subject-wise link:

Tips, Tricks, and Strategies to Prepare For Excretory Products and Their Elimination

This table outlines effective tips and strategies to master the topic of Excretory Products and Their Elimination.

Tips/Tricks	Description
Use Mnemonics	Create phrases to remember key concepts (e.g., "Urea is less toxic than ammonia").
Visual Aids	Utilise diagrams of the human excretory system to visualise organs and functions.
Practice Past Papers	Solve previous years' questions to familiarise yourself with exam patterns.
Group Study	Discuss topics with peers to reinforce learning through teaching.
Flashcards	Make flashcards for important terms like "glomerular filtration rate" and "micturition."

Weightage of Topics in Different Entrance Exams

Understanding the weightage of topics can help prioritise your study efforts in Excretory Products and Their Elimination for various entrance exams.

Entrance Exam	Weightage (%)	Important Topics
NEET	25%	Excretion definition: Human excretory system
AIIMS	30%	Disorders of the excretory system
CBSE Class 11	20%	Urine formation, micturition

Types of Questions Asked on the Topic in Different Exams

Familiarising yourself with the types of questions related to Excretory Products and Their Elimination can improve your exam performance.

Entrance Exam	Types of Questions
NEET	Conceptual questions, diagram labelling
AIIMS	Case studies related to excretory disorders
CBSE Class 12	Short answer questions, long answer explanations

Use this structured approach to help you prepare effectively for the chapter on Excretory Products and Their Elimination in your biology curriculum. With mnemonics, visual aids, and practice questions, critical concepts will be better understood and retained.

One of the most critical concepts that the student aspirant to a career in biology needs to know is that of excretory products and their elimination, especially those taking NEET exams. Such knowledge not only keeps one learning but also makes one more conscious of the functions occurring within the body.