Welcome to the course material on Excretion in Biology. Excretion is a vital process in living organisms that involves the removal of waste products and excess materials to maintain homeostasis within the body. The significance of excretion lies in the elimination of harmful substances such as metabolic wastes, which if allowed to accumulate, can disrupt cellular functions and overall health.

When we delve into the types of excretory structures, we encounter various mechanisms organisms employ to rid themselves of waste. These structures include the contractile vacuole, flame cell, nephridium, Malpighian tubule, kidney, stoma, and lenticel. Each of these structures is uniquely adapted to perform specific excretory functions and maintain osmotic balance within the organism.

The kidneys play a crucial role in excretion and osmoregulation in vertebrates. These bean-shaped organs filter blood, reabsorb essential substances, and excrete waste products in the form of urine. The intricate structure of the kidneys, including nephrons and renal tubules, enables them to regulate the body's fluid and electrolyte balance effectively.

Furthermore, lungs and skin also contribute to excretion in organisms. Lungs eliminate carbon dioxide, a byproduct of cellular respiration, during exhalation. The skin, through sweat glands, excretes water, salts, and small amounts of urea. Understanding the functions of these excretory organs provides insight into how organisms maintain internal balance by removing waste products.

Shifting our focus to plants, excretory products play a significant role in their physiology. Plants release oxygen during photosynthesis, a byproduct that is essential for the survival of many organisms. Additionally, plants secrete tannins, resins, gums, mucilage, and alkaloids, which serve diverse functions such as defense mechanisms, attracting pollinators, and promoting growth.

In conclusion, the study of excretion unveils the intricate mechanisms organisms employ to eliminate waste products and maintain internal balance. By exploring the structures, functions, and economic importance of excretory products, we gain a deeper understanding of the fundamental processes that sustain life across various biological systems.


  1. Understand the meaning and significance of excretion
  2. Explore the economic importance of excretory products in plants
  3. Analyze the functions and excretory products of the lungs and skin
  4. Relate the characteristics of excretory structures to their functions

Lesson Note

Excretion is a vital process in living organisms that involves the removal of metabolic waste products from the body. These waste products are the result of biochemical reactions that occur in cells to sustain life. It is essential for maintaining homeostasis and ensuring the body operates efficiently.

Lesson Evaluation

Congratulations on completing the lesson on Excretion. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

  1. Which of the following excretory structures is found in organisms such as Amoeba and Paramecium? A. Kidney B. Nephridium C. Contractile vacuole D. Malpighian tubule Answer: C. Contractile vacuole
  2. Which excretory mechanism is responsible for eliminating carbon dioxide from the body? A. Kidneys B. Lungs C. Liver D. Skin Answer: B. Lungs
  3. The excretory product mainly eliminated through the skin in humans is: A. Urea B. Carbon dioxide C. Salt D. Water Answer: B. Carbon dioxide
  4. Which of the following excretory structures is most commonly found in insects and arachnids? A. Flame cell B. Nephridium C. Malpighian tubule D. Kidney Answer: C. Malpighian tubule
  5. The main excretory product of plants during photosynthesis is: A. Glucose B. Oxygen C. Water D. Carbon dioxide Answer: D. Carbon dioxide
  6. Which excretory organ is responsible for the regulation of electrolytes and fluid balance in the body? A. Lungs B. Skin C. Kidneys D. Liver Answer: C. Kidneys
  7. Which excretory product is responsible for the bitterness of certain plants and acts as a deterrent to herbivores? A. Oxygen B. Tannins C. Mucilage D. Resins Answer: B. Tannins
  8. The process of eliminating metabolic waste products in the form of sweat is primarily carried out by which excretory structure? A. Lungs B. Kidneys C. Skin D. Liver Answer: C. Skin
  9. Which of the following excretory products of plants is involved in defense mechanisms against herbivores and pathogens? A. Oxygen B. Carbon dioxide C. Alkaloids D. Gums Answer: C. Alkaloids
  10. The excretory organ responsible for the removal of nitrogenous waste in humans is: A. Lungs B. Liver C. Kidneys D. Skin Answer: C. Kidneys

Recommended Books

Past Questions

Wondering what past questions for this topic looks like? Here are a number of questions about Excretion from previous years

Question 1 Report

Which of the following functions of the body are nephrons associated with?

Question 1 Report

The waste product of insects is?

Question 1 Report

The diagram above is an illustration of the longitudinal section of a mammalian organ. Study it and answer this question.

What is the main function of the organ?

Practice a number of Excretion past questions