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Excretion [Free JAMB Tutorial on Biology]

This Biology Tutorial will focus on EXCRETION. This topic has been explained to ensure you understand it very well. At the end of the tutorial, you can download it for FREE. Please share this page with your friends who may need it.

This tutorial will try to explain everything you need to know about the excretory system while focusing on the types of excretory structures, excretory mechanisms, and excretory products of plants.

After the tutorial, we give you some practice questions to help you understand the topic even better.

Let’s get on with it.

What’s Excretion

Excretion is the process by which waste products of metabolism and other non-useful materials are eliminated from an organism’s body. The primary purpose of excretion is to rid the body of substances that could be harmful if they were to accumulate to excessive levels.

In humans and many other organisms, the major organs involved in excretion include the kidneys, which filter waste products from the blood to form urine; the lungs, which eliminate carbon dioxide during respiration; the skin, which releases sweat containing various waste products; and the liver, which plays a role in the elimination of certain metabolic byproducts.

Excretion helps maintain homeostasis by regulating the internal environment of an organism and ensuring that concentrations of various substances remain within acceptable limits. It is a crucial physiological process for the overall health and functioning of living organisms.

Significance of Excretion

Excretion is a crucial physiological process with several significant functions and importance for the overall health and functioning of living organisms. Some of the key significance of excretion includes:

  1. Waste Elimination: Excretion helps remove metabolic waste products and toxins from the body. These waste materials, if allowed to accumulate, can be harmful and disrupt the normal functioning of cells and organs.
  2. Maintaining Homeostasis: By regulating the concentrations of various substances such as ions, water, and metabolic byproducts, excretion contributes to maintaining a stable internal environment, known as homeostasis. Homeostasis is vital for the proper functioning of cells and tissues.
  3. Osmoregulation: Excretion, especially through processes like urine formation in the kidneys, plays a crucial role in regulating the osmotic balance of the body. It helps control the concentration of salts and water, ensuring that the body’s internal environment is suitable for cellular functions.
  4. Acid-Base Balance: Excretion processes, particularly through the kidneys, contribute to the regulation of the body’s pH levels. The elimination of acidic or basic substances helps keep the blood and bodily fluids within the appropriate pH range for optimal biochemical reactions.
  5. Regulation of Blood Pressure: The kidneys play a significant role in regulating blood pressure by controlling the volume of blood and the concentration of electrolytes in the blood. Proper excretion helps maintain blood pressure within a normal range.
  6. Elimination of Nitrogenous Waste: Many metabolic processes in organisms produce nitrogenous waste products such as urea and ammonia. Excretion, particularly through the urinary system, helps eliminate these nitrogenous compounds, preventing their accumulation, which can be toxic.
  7. Temperature Regulation: In some organisms, excretion through processes like sweating contributes to the regulation of body temperature. Sweating allows for the dissipation of excess heat, helping to cool the body.

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Types of Excretory Structures

Different organisms have evolved various excretory structures to eliminate waste products and maintain homeostasis.

The types of excretory structures vary across species, reflecting adaptations to different environments and physiological needs.

Here are some examples of excretory structures in different organisms:

  1. Contractile Vacuole:
    • Found in: Protists (single-celled organisms), such as amoebas and paramecia.
    • Structure and Function: Contractile vacuoles are membrane-bound organelles that periodically collect excess water and waste materials from the cell’s cytoplasm. The vacuole then contracts, expelling its contents outside the cell through a pore. This process helps regulate the water balance within the cell.
  2. Flame Cell (Protonephridium):
    • Found in: Flatworms (platyhelminthes).
    • Structure and Function: Flame cells are specialized cells with a tuft of cilia that resemble a flickering flame. They are part of a network of tubules (protonephridia) that extract waste products and excess water from the interstitial fluid. The cilia create a current that moves fluids through the tubules and expels waste through pores in the body wall.
  3. Nephridium:
    • Found in: Annelids (earthworms, leeches), some mollusks.
    • Structure and Function: Nephridia are tubular structures that filter coelomic fluid. They extract nitrogenous wastes and excess water, concentrating them into urine. The urine is then expelled from the body through openings called nephridiopores.
  4. Malpighian Tubule:
    • Found in: Insects, arachnids, some myriapods.
    • Structure and Function: Malpighian tubules are blind-ended tubes that extend into the hemolymph (insect blood). They extract nitrogenous waste, ions, and other solutes from the hemolymph, forming a filtrate that is modified in the tubules. The waste is then excreted as solid material along with feces.
  5. Kidney:
    • Found in: Vertebrates (fish, amphibians, reptiles, birds, mammals).
    • Structure and Function: The kidney is a complex organ with nephrons as functional units. Nephrons filter blood, reabsorb essential substances, and excrete nitrogenous waste as urine. The urine is then transported to the bladder and expelled from the body through the urethra.
  6. Stoma:
    • Found in: Plants, specifically in the epidermis (outer layer) of leaves.
    • Structure and Function: Stomata are tiny pores surrounded by specialized cells known as guard cells. They regulate the exchange of gases (such as oxygen and carbon dioxide) and water vapor between the plant and the atmosphere. While stomata are not primarily excretory structures, they play a role in controlling water loss and gas exchange.
  7. Lenticel:
    • Found in: Plants, particularly in the bark of woody stems.
    • Structure and Function: Lenticels are small openings in the bark of plants that allow for gas exchange between internal tissues and the external environment. They help facilitate the exchange of gases (such as oxygen and carbon dioxide) during respiration. While lenticels are not excretory structures, they contribute to the overall gas exchange and aeration of plant tissues.

Excretory Mechanisms

Excretion Mechanisms in Human Beings, Image Credit: CareerPower.in

The excretory mechanisms in the human body involve various organs and systems that work together to eliminate waste products and maintain homeostasis.

The three main excretory organs are the kidneys, lungs, and skin. Each of these organs plays a specific role in removing different types of waste from the body.

  1. Kidneys:
    • Function: The kidneys are primary excretory organs that filter the blood to remove waste products and excess substances. The functional units of the kidneys are called nephrons. Nephrons filter the blood, reabsorb essential substances, and excrete waste in the form of urine.
    • Specific Substances Excreted: Nitrogenous wastes (urea, creatinine), excess salts, water, and other metabolic byproducts.
    • Regulation of Water and Electrolyte Balance: The kidneys help regulate the concentration of ions (sodium, potassium, etc.) and water in the body, contributing to the maintenance of proper blood pressure and overall homeostasis.
  2. Lungs:
    • Function: The lungs are involved in the excretion of carbon dioxide, a waste product of cellular respiration. During respiration, oxygen is taken in, and carbon dioxide is produced. The lungs facilitate the exchange of these gases with the external environment.
    • Specific Substances Excreted: Carbon dioxide (CO2).
    • Regulation of Acid-Base Balance: The removal of carbon dioxide by the lungs helps regulate the pH of the blood and maintain acid-base balance in the body.
  3. Skin:
    • Function: The skin is the largest organ of the body and is involved in the excretion of certain waste products through the process of sweating. Sweat glands in the skin release a watery solution that contains electrolytes and small amounts of metabolic waste.
    • Specific Substances Excreted: Water, electrolytes (sodium, chloride), urea, and other small amounts of metabolic waste.
    • Regulation of Body Temperature: Sweating also plays a crucial role in thermoregulation by dissipating heat through the evaporation of sweat from the skin’s surface.

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Economic Importance of the Excretory Products of Plants

The economic importance of various excretory products of plants is vast, as these substances often have commercial, industrial, medicinal, or agricultural applications.

Here’s a brief overview of the economic significance of some plant excretory products:

  1. Oxygen:
    • Economic Importance: Oxygen produced during photosynthesis is crucial for the survival of aerobic organisms, including humans and animals. Additionally, the process of photosynthesis is fundamental to many industrial applications, such as in the production of food, textiles, and bioenergy.
  2. Carbon Dioxide:
    • Economic Importance: Carbon dioxide released during respiration is used by plants during photosynthesis. In controlled environments like greenhouses, increased levels of carbon dioxide can enhance plant growth and crop yields, leading to improved agricultural productivity.
  3. Tannins:
    • Economic Importance: Tannins are polyphenolic compounds found in various plant tissues, and they have commercial value in industries such as tanning and dyeing. Tannins are used to tan leather, clarify beverages, and manufacture inks and dyes.
  4. Resins:
    • Economic Importance: Resins are sticky, viscous substances produced by certain plants. They have various applications, including the production of adhesives, varnishes, and coatings. Resins from certain trees, like pine trees, are used to produce turpentine and rosin.
  5. Gums and Mucilage:
    • Economic Importance: Gums and mucilage are substances that form gels when mixed with water. They have applications in the food industry as thickening agents, stabilizers, and emulsifiers. They are also used in pharmaceuticals, cosmetics, and various industrial processes.
  6. Alkaloids:
    • Economic Importance: Alkaloids are nitrogen-containing compounds with diverse physiological effects. Many alkaloids have medicinal properties and are used in the pharmaceutical industry. Examples include morphine (from opium poppy) and quinine (from cinchona bark).
  7. Essential Oils:
    • Economic Importance: Essential oils are volatile aromatic compounds produced by certain plants. They have various applications in the fragrance, cosmetic, and food industries. Essential oils are also used in traditional medicine and aromatherapy.
  8. Latex:
    • Economic Importance: Latex is a milky fluid produced by some plants, such as rubber trees. Natural rubber is derived from latex and is a crucial commodity with applications in the manufacturing of tires, medical products, and various industrial goods.

That’s all we will cover in this tutorial. Now attempt these questions to challenge your knowledge of understanding on the topic.

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Practice Questions

1: What is the primary purpose of excretion in living organisms?
A) Nutrient absorption
B) Waste elimination
C) Energy production
D) Oxygen transport

2. In which organism would you find a contractile vacuole as an excretory structure?
A) Earthworm
B) Amoeba
C) Insect
D) Fish

3. How do the lungs contribute to excretion in humans?
A) Filtering blood
B) Releasing sweat
C) Eliminating carbon dioxide
D) Producing urine

4. Apart from its role in respiration, what economic benefit does oxygen provide?
A) Fuel for industries
B) Food production
C) Enhancement of plant growth
D) Industrial dyeing

5. What is the primary function of flame cells in flatworms?
A) Gas exchange
B) Osmoregulation
C) Blood filtration
D) Vision

6. Where are Malpighian tubules found in insects?
A) Wings
B) Abdomen
C) Head
D) Thorax

7: Which of the following is a plant excretory product used in the tanning industry?
A) Oxygen
B) Tannins
C) Carbon dioxide
D) Mucilage

8: What is the primary function of lenticels in plants?
A) Gas exchange
B) Water absorption
C) Root anchorage
D) Nutrient storage

9: What is the functional unit of the kidney responsible for urine formation?
A) Nephron
B) Glomerulus
C) Tubule
D) Cortex

10: Which industry commonly uses resins derived from plants?
A) Textile
B) Construction
C) Food
D) Perfume

11: How does the process of transpiration in plants contribute to excretion?
A) Release of oxygen
B) Elimination of excess water
C) Removal of nitrogenous waste
D) Production of tannins

12: In which industry are gums and mucilage commonly used as thickening agents?
A) Pharmaceutical
B) Construction
C) Automotive
D) Electronics

13: What is the primary reason for the economic importance of alkaloids?
A) Food flavoring
B) Medicinal properties
C) Dyeing
D) Textile production

14: How do the lungs contribute to the regulation of acid-base balance in the body?
A) Release of carbon dioxide
B) Production of urea
C) Removal of excess salts
D) Filtration of blood

15: What commercial product is derived from the latex produced by certain plants?
A) Paper
B) Rubber
C) Textiles
D) Fuel additives

That’s all. Before you check the correct answers, first write down your own answers.

THINK & ACT : If we can give you this for FREE, imagine what we can give if you pay and join the ALLSCHOOL JAMB Online Lesson. In the lesson, our hardworking tutors ensure they only teach you things that will come out in JAMB, so you’ll score extremely high in JAMB. Click Here to join the ALLSCHOOL JAMB Online Lesson NOW.

Answers and Explanations to the Practice Questions

1. Answer: B) Waste elimination
Explanation: The primary purpose of excretion is to eliminate waste products from the body, maintaining internal balance and preventing the accumulation of harmful substances.

2. Answer: B) Amoeba
Explanation: Contractile vacuoles are found in single-celled organisms like amoebas. They help regulate water balance by expelling excess water from the cell.

3. Answer: C) Eliminating carbon dioxide
Explanation: Lungs contribute to excretion by removing carbon dioxide, a waste product of cellular respiration, from the body.

4. Answer: C) Enhancement of plant growth
Explanation: Oxygen produced during photosynthesis is vital for plant growth, and healthy plant growth contributes to various economic sectors like agriculture.

5. Answer: B) Osmoregulation
Explanation: Flame cells in flatworms play a role in regulating water and ion balance in the organism.

6. Answer: B) Abdomen
Explanation: Malpighian tubules in insects are located in the abdomen and are involved in the excretion of nitrogenous waste.

7. Answer: B) Tannins
Explanation: Tannins are plant excretory products used in the tanning industry for leather processing.

8. Answer: A) Gas exchange
Explanation: Lenticels in plants facilitate gas exchange between internal tissues and the external environment.

9. Answer: A) Nephron
Explanation: The nephron is the functional unit of the kidney responsible for urine formation through blood filtration and reabsorption.

10. Answer: B) Construction
Explanation: Resins derived from plants are used in construction for adhesives, coatings, and varnishes.

11. Answer: B) Elimination of excess water
Explanation: Transpiration in plants helps eliminate excess water from the plant’s tissues.

12. Answer: A) Pharmaceutical
Explanation: Gums and mucilage are used in the pharmaceutical industry as thickening agents in various formulations.

13. Answer: B) Medicinal properties
Explanation: Alkaloids have medicinal properties, and many drugs are derived from plant alkaloids.

14. Answer: A) Release of carbon dioxide
Explanation: Lungs contribute to the regulation of acid-base balance by eliminating carbon dioxide.

15. Answer: B) Rubber
Explanation: Latex from certain plants, like rubber trees, is used in the production of natural rubber.

So how many did you get? Share it with us in the comment section below.

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